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Introduction: Shivering is a common side effect after general anesthesia. Risk factors are hypothermia, young age and postoperative pain. Severe complications of shivering are rare but can occur due to increased oxygen consumption. Previous systematic reviews are outdated and have summarized the evidence on the topic using only pairwise comparisons. The objective of this manuscript was a quantitative synthesis of evidence on pharmacological interventions to treat postanesthetic shivering., Evidence Acqusition: Systematic review and frequentist network meta-analysis using the R package netmeta. Endpoints were the risk ratio (RR) of persistent shivering at one, five and 10 minutes after treatment with saline/placebo as the comparator. Data were retrieved from Medline, Embase, Central and Web of Science up to January 2022. Eligibility criteria were: randomized, controlled, and blinded trials comparing pharmacological interventions to treat shivering after general anesthesia. Studies on shivering during or after any type of regional anesthesia were excluded as well as sedated patients after cardiac surgery., Evidence Synthesis: Thirty-two trials were eligible for data synthesis, including 28 pharmacological interventions. The largest network included 1431 patients. The network geometry was two-centered with most comparisons linked to saline/placebo or pethidine. The best interventions were after one minute: doxapram 2 mg/kg, tramadol 2 mg/kg and nefopam 10 mg, after 5 minutes: tramadol 2 mg/kg, nefopam 10 mg and clonidine 150 µg and after 10 minutes: nefopam 10 mg, methylphenidate 20 mg and tramadol 1 mg/kg, all reaching statistical significance. Pethidine 25 mg and clonidine 75 µg also performed well and with statistical significance in all networks., Conclusions: Nefopam, tramadol, pethidine and clonidine are the most effective treatments to stop postanesthetic shivering. The efficacy of doxapram is uncertain since different doses showed contradictory effects and the evidence for methylphenidate is based on a single comparison in only one network. Furthermore, both lack data on side effects. Further studies are needed to clarify the efficacy of dexmedetomidine to treat postanesthetic shivering.

Exposure of Drosophila skeletal muscle to bacterial lipopolysaccharides (LPS) rapidly and transiently hyperpolarizes membrane potential. However, the mechanism responsible for hyperpolarization remains unclear. The resting membrane potential of the cells is maintained through multiple mechanisms. This study investigated the possibility of LPS activating calcium-activated potassium channels (K Ca ) and/or K2p channels. 2-Aminoethyl diphenylborinate (2-APB), blocks uptake of Ca 2+ into the endoplasmic reticulum (ER); thus, limiting release from ryanodine-sensitive internal stores to reduce the function of K Ca channels. Exposure to 2-APB produces waves of hyperpolarization even during desensitization of the response to LPS and in the presence of doxapram. This finding in this study suggests that doxapram blocked the acid-sensitive K2p tandem-pore channel subtype known in mammals. Doxapram blocked LPS-induced hyperpolarization and depolarized the muscles as well as induced motor neurons to produce evoked excitatory junction potentials (EJPs). This was induced by depolarizing motor neurons, similar to the increase in extracellular K + concentration. The hyperpolarizing effect of LPS was not blocked by decreased extracellular Ca 2+ or the presence of Cd 2+ . LPS appears to transiently activate doxapram sensitive K2p channels independently of K Ca channels in hyperpolarizing the muscle. Septicemia induced by gram-negative bacteria results in an increase in inflammatory cytokines, primarily induced by bacterial LPS. Currently, blockers of LPS receptors in mammals are unknown; further research on doxapram and other K2p channels is warranted. (220 words)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The resting membrane potential of most cells is maintained by potassium K2p channels. The pharmacological profile and distribution of various K2p channel subtypes in organisms are still being investigated. The Drosophila genome contains 11 subtypes; however, their function and expression profiles have not yet been determined. Doxapram is clinically used to enhance respiration in humans and blocks the acid-sensitive K2p TASK subtype in mammals. The resting membrane potential of larval Drosophila muscle and synaptic transmission at the neuromuscular junction are pH sensitive. The present study investigated the effects of doxapram on membrane potential and synaptic transmission using intracellular recordings of larval Drosophila muscles. Doxapram (1 mM and 10 mM) depolarizes the muscle and appears to depolarize motor neurons, causing an increase in the frequency of spontaneous quantal events and evoked excitatory junction potentials. Verapamil (1 and 10 mM) paralleled the action of doxapram. These changes were matched by an extracellular increase in KCl (50 mM) and blocked by Cd 2+ . It is assumed that the motor nerve depolarizes to open voltage-gated Ca 2+ channels in presynaptic nerve terminals because of exposure to doxapram. These findings are significant for building models to better understand the function of pharmacological agents that affect K2p channels and how K2p channels contribute to the physiology of tissues. Drosophila offers a genetically amenable model that can alter the tissue-specific expression of K2p channel subtypes to simulate known human diseases related to this family of channels., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this study., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Bacterial septicemia is commonly induced by Gram-negative bacteria. The immune response is triggered in part by the secretion of bacterial endotoxin lipopolysaccharide (LPS). LPS induces the subsequent release of inflammatory cytokines which can result in pathological conditions. There is no known blocker to the receptors of LPS. The Drosophila larval muscle is an amendable model to rapidly screen various compounds that affect membrane potential and synaptic transmission such as LPS. LPS induces a rapid hyperpolarization in the body wall muscles and depolarization of motor neurons. These actions are blocked by the compound doxapram (10 mM), which is known to inhibit a subtype of the two-P-domain K+ channel (K2P channels). However, the K2P channel blocker PK-THPP had no effect on the Drosophila larval muscle at 1 and 10 mM. These channels are activated by chloroform, which also induces a rapid hyperpolarization of these muscles, but the channels are not blocked by doxapram. Likewise, chloroform does not block the depolarization induced by doxapram. LPS blocks the postsynaptic glutamate receptors on Drosophila muscle. Pre-exposure to doxapram reduces the LPS block of these ionotropic glutamate receptors. Given that the larval Drosophila body wall muscles are depolarized by doxapram and hyperpolarized by chloroform, they offer a model to begin pharmacological profiling of the K2P subtype channels with the potential of identifying blockers for the receptors to mitigate the actions of the Gram-negative endotoxin LPS.

Objective: This study aimed to evaluate the change in the waveform pattern of the electrical activity of the diaphragm (Edi) following the administration of doxapram in extremely preterm infants ventilated with neurally adjusted ventilatory assist (NAVA)., Study Design: We conducted this retrospective cohort study in our neonatal intensive care unit between November 2019 and September 2021. The study participants were extremely preterm infants under the gestational age of 28 weeks who were ventilated with NAVA and administered doxapram. We collected the data of the Edi waveform pattern and calculated the proportion. To analyze the change in the proportion of the Edi waveform pattern, we compared the proportion of the data for 1 h before and after doxapram administration., Results: Ten extremely preterm infants were included. Almost all the patients' respiratory condition improved after doxapram administration. The ventilatory parameters-Edi peak, Edi minimum, peak inspiratory pressure, time in backup ventilation, and number of switches to backup ventilation-did not change significantly. However, the proportion of phasic pattern significantly increased (before: 46% vs. after: 72%; p < 0.05), whereas the central apnea pattern significantly decreased after doxapram administration (before: 31% vs. after: 8.3%; p < 0.05). The proportion of irregular low-voltage patterns tended to decrease, albeit with no significant changes., Conclusion: Our results indicated that the proportion of Edi waveform patterns changed following doxapram administration. Edi waveform pattern analysis could be a sensitive indicator of effect with other intervention for respiratory conditions., (© 2022 Wiley Periodicals LLC.)

Objective: To compare the effects of two doses of doxapram intravenous injection and carbon dioxide inhalation on the cardiovascular and laryngeal functions of anesthetized hounds., Study Design: Experimental study., Animals: Six healthy adult dogs., Methods: In a Latin-square design, the mean arterial blood pressure (MABP) and heart rate (HR) were recorded continuously. The inspiratory normalized glottic gap areas (iNGGA) were measured before and after each stimulation with 0.55 mg/kg of doxapram (L-DOX), 2.2 mg/kg of doxapram (H-DOX), or 90 s of inhalation of 10% carbon dioxide in oxygen (I-CO 2 ). The stimulations were tested in duplicate or triplicate. Video clips of the laryngeal movement were scored by board-certified surgeons masked to the treatment., Results: The MABP increased with L-DOX and H-DOX up to 81% (both p < .001 compared to I-CO 2 ), and persisted during the other stimulations (both p < .001). An intermittent tachycardic effect of up to 79% increase in HR was observed with doxapram. The HR following H-DOX was higher than L-DOX and I-CO 2 (both p < .016). Neither hypertension nor tachycardia was observed with I-CO 2 . The iNGGA increased with all treatments (p < .001). The iNGGA was greater with H-DOX than L-DOX and I-CO 2 (both p < .007). All treatments received higher scores (all p < .001) with acceptable inter- and intra-observers Krippendorff's alphas., Conclusion: All treatments were effective respiratory stimulants in anesthetized dogs; however, doxapram caused hypertension and tachycardia., Clinical Significance: Carbon dioxide inhalation might improve arytenoid motion without cardiovascular effects in dogs during clinical airway examinations., (© 2021 American College of Veterinary Surgeons.)

Panic disorder can be categorized into the nonrespiratory or the respiratory subtypes, the latter comprising dyspnea, shortness of breath, chest pain, feelings of suffocation, and paresthesias. Doxapram is an analeptic capable of inducing panic attacks with respiratory symptoms in individuals diagnosed with the disorder; however, its neuroanatomical targets and its effects on experimental animals remain uncharacterized. One of the brain regions proposed to trigger panic attacks is the midbrain periaqueductal gray (PAG). Therefore, in this study, we evaluated the effects of doxapram in Fos (c-Fos) protein expression in the PAG and characterized its cardiorespiratory and behavioral effects on the elevated T maze and in the conditioned place aversion (CPA) paradigms. Doxapram increased Fos expression in different columns of the PAG, increased respiratory frequency, decreased heart rate, and increased arterial pressure when injected via intravenous route. Alprazolam, a panicolytic benzodiazepine, injected via intraperitoneal route, decreased respiratory frequency, whereas URB597, an anandamide hydrolysis inhibitor injected via intraperitoneal route, was ineffective. Doxapram injected via intraperitoneal route induced an anxiogenic-like effect in the elevated T-maze model; however, it failed to induce CPA. This study suggests that the cardiorespiratory and behavioral effects of doxapram in rodents serve as an experimental model that can provide insights into the neurobiology of panic attacks., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Objective: To determine the effects of dexmedetomidine, doxapram, and dexmedetomidine plus doxapram on ventilation ([Formula: see text]e), breath frequency, and tidal volume (Vt) in ball pythons ( Python regius ) and of doxapram on the thermal antinociceptive efficacy of dexmedetomidine., Animals: 14 ball pythons., Procedures: Respiratory effects of dexmedetomidine and doxapram were assessed with whole-body, closed-chamber plethysmography, which allowed for estimates of [Formula: see text]e and Vt. In the first experiment of this study with a complete crossover design, snakes were injected, SC, with saline (0.9% NaCl) solution, dexmedetomidine (0.1 mg/kg), doxapram (10 mg/kg), or dexmedetomidine and doxapram, and breath frequency, [Formula: see text]e, and Vt were measured before and every 30 minutes thereafter, through 240 minutes. In the second experiment, antinociceptive efficacy of saline solution, dexmedetomidine, and dexmedetomidine plus doxapram was assessed by measuring thermal withdrawal latencies before and 60 minutes after SC injection., Results: Dexmedetomidine significantly decreased breath frequency and increased Vt but did not affect [Formula: see text]e at all time points, compared with baseline. Doxapram significantly increased [Formula: see text]e, breath frequency, and Vt at 60 minutes after injection, compared with saline solution. The combination of dexmedetomidine and doxapram, compared with dexmedetomidine alone, significantly increased [Formula: see text]e at 30 and 60 minutes after injection and did not affect breath frequency and Vt at all time points. Thermal withdrawal latencies significantly increased when snakes received dexmedetomidine or dexmedetomidine plus doxapram, versus saline solution., Conclusions and Clinical Relevance: Concurrent administration of doxapram may mitigate the dexmedetomidine-induced reduction of breathing frequency without disrupting thermal antinociceptive efficacy in ball pythons.

Background: Endoscopic retrograde cholangiopancreatography (ERCP) requires moderate to deep sedation, usually with propofol. Adverse effects of propofol sedation are relatively common, such as respiratory and cardiovascular depression. This study was conducted to determine if doxapram, a respiratory stimulant, could be used to reduce the incidence of respiratory depression., Methods: This is a single-center, prospective randomized double-blind study performed in the endoscopy unit of Helsinki University Central Hospital. 56 patients were randomized in a 1:1 ratio to either receive doxapram as an initial 1 mg/kg bolus and an infusion of 1 mg/kg/h (group DOX) or placebo (group P) during propofol sedation for ERCP. Main outcome measures were apneic episodes and hypoxemia (SpO 2  < 90%). Mann-Whitney test for continuous variables and Fisher's exact test for discrete variables were used and mixed effects modeling to take into account repeated measurements on the same subject and comparing both changes within a group as a function of time and between the groups., Results: There were no statistically significant differences in apneic episodes (p = 0.18) or hypoxemia (p = 0.53) between the groups. There was a statistically significant rise in etCO 2 levels in both groups, but the rise was smaller in group P. There was a statistically significant rise in Bispectral Index (p = 0.002) but not modified Observer's Assessment of Agitation/Sedation (p = 0.21) in group P. There were no statistically significant differences in any other measured parameters., Conclusions: Doxapram was not effective in reducing respiratory depression caused by deep propofol sedation during ERCP. Further studies are warranted using different sedation protocols and dosing regimens. Clinical trial registration ClinicalTrials.gov ID NCT02171910.

Aims: The mode of action by which doxapram acts as a respiratory stimulant in humans is controversial. Studies in rodent models, have shown that doxapram is a more potent and selective inhibitor of TASK-1 and TASK-1/TASK-3 heterodimer channels, than TASK-3. Here we investigate the direct effect of doxapram and chirally separated, individual positive and negative enantiomers of the compound, on both human and mouse, homodimeric and heterodimeric variants of TASK-1 and TASK-3., Methods: Whole-cell patch clamp electrophysiology on tsA201 cells was used to assess the potency of doxapram on cloned human or mouse TASK-1, TASK-3 and TASK-2 channels. Mutations of amino acids in the pore-lining region of TASK-3 channels were introduced using site-directed mutagenesis., Results: Doxapram was an equipotent inhibitor of human TASK-1 and TASK-3 channels, compared with mouse channel variants, where it was more selective for TASK-1 and heterodimers of TASK-1 and TASK-3. The effect of doxapram could be attenuated by either the removal of the C-terminus of human TASK-3 channels or mutations of particular hydrophobic residues in the pore-lining region. These mutations, however, did not alter the effect of a known extracellular inhibitor of TASK-3, zinc. The positive enantiomer of doxapram, GAL-054, was a more potent antagonist of TASK channels, than doxapram, whereas the negative enantiomer, GAL-053, had little inhibitory effect., Conclusion: These data show that in contrast to rodent channels, doxapram is a potent inhibitor of both TASK-1 and TASK-3 human channels, providing further understanding of the pharmacological profile of doxapram in humans and informing the development of new therapeutic agents., (© 2019 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)

Background: Opioids are potent painkillers but come with serious adverse effects ranging from addiction to potentially lethal respiratory depression. A variety of drugs with separate mechanisms of action are available to prevent or reverse opioid-induced respiratory depression (OIRD)., Methods: The authors reviewed human studies on reversal of OIRD using models that describe and predict the time course of pharmacokinetics (PK) and pharmacodynamics (PD) of opioids and reversal agents and link PK to PD., Results: The PKPD models differ in their basic structure to capture the specific pharmacological mechanisms by which reversal agents interact with opioid effects on breathing. The effect of naloxone, a competitive opioid receptor antagonist, is described by the combined effect-compartment receptor-binding model to quantify rate limitation at the level of drug distribution and receptor kinetics. The effects of reversal agents that act through non-opioidergic pathways, such as ketamine and the experimental drug GAL021, are described by physiological models, in which stimulants act at CO 2 chemosensitivity, CO 2 -independent ventilation, or both. The PKPD analyses show that although all reversal strategies may be effective under certain circumstances, there are conditions at which reversal is less efficacious and sometimes even impossible., Conclusions: Model-based drug development is needed to design an 'ideal' reversal agent-that is, one that is not influenced by opioid receptor kinetics, does not interfere with opioid analgesia, has a rapid onset of action with long-lasting effects, and is devoid of adverse effects., (Copyright © 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.)

Doxapram is a respiratory stimulant used for decades as a treatment option in apnea of prematurity refractory to methylxanthine treatment. Its mode of action, however, is still poorly understood. We investigated direct effects of doxapram on the pre-Bötzinger complex (PreBötC) and on a downstream motor output system, the hypoglossal nucleus (XII), in the transverse brainstem slice preparation. While doxapram has only a modest stimulatory effect on frequency of activity generated within the PreBötC, a much more robust increase in the amplitude of population activity in the subsequent motor output generated in the XII was observed. In whole cell patch-clamp recordings of PreBötC and XII neurons, we confirmed significantly increased firing of evoked action potentials in XII neurons in the presence of doxapram, while PreBötC neurons showed no significant alteration in firing properties. Interestingly, the amplitude of activity in the motor output was not increased in the presence of doxapram compared with control conditions during hypoxia. We conclude that part of the stimulatory effects of doxapram is caused by direct input on brainstem centers with differential effects on the rhythm generating kernel (PreBötC) and the downstream motor output (XII). NEW & NOTEWORTHY The clinically used respiratory stimulant doxapram has distinct effects on the rhythm generating kernel (pre-Bötzinger complex) and motor output centers (nucleus hypoglossus). These effects are obliterated during hypoxia and are mediated by distinct changes in the intrinsic properties of neurons of the nucleus hypoglossus and synaptic transmission received by pre-Bötzinger complex neurons.

Objective: To determine the influence of propofol or methohexital, with and without doxapram, on the examination of laryngeal function in dogs., Study Design: Experimental study., Animals: Forty healthy dogs randomly assigned to 4 groups: propofol with saline (n = 10), propofol with doxapram (n = 10), methohexital with saline (n = 10), or methohexital with doxapram (n = 10)., Methods: Propofol and methohexital were administered to effect. Investigators examined laryngeal function (initial) simultaneously with video laryngoscopy. Doxapram or saline was administered, and laryngeal function was reevaluated (second). Laryngeal motion, quality of laryngeal exposure, and the degree of swallowing, laryngospasm, and jaw tone were scored at each evaluation. Adverse events were recorded. Initial and second videos were evaluated by a masked observer, and still images obtained from both evaluations were evaluated for change in rima glottidis size by 2 masked observers., Results: Administration of doxapram and saline was delayed with propofol (P = .001). Laryngeal function did not differ between dogs receiving propofol or methohexital, irrespective of doxapram administration. Doxapram improved breathing scores in both groups (P < .001). Jaw tone increased with propofol during the second evaluation (P = .049). Swallowing was more prevalent at initial examination (P = .020). Methohexital resulted in an increased heart rate (P < .001) compared with propofol. Twenty-five percent of dogs receiving methohexital developed seizure-like activity (n = 5/20)., Conclusion: Evaluation of laryngeal function did not differ between healthy dogs anesthetized with propofol or methohexital. Methohexital provided shorter examination times with less jaw tone but was associated with adverse events., Clinical Significance: This study provides evidence to recommend propofol over methohexital as an induction agent for laryngeal function examination., (© 2018 The Authors. Veterinary Surgery published by Wiley Periodicals, Inc. on behalf of The American College of Veterinary Surgeons.)

Sensing of hypoxia and acidosis in arterial chemoreceptors is thought to be mediated through the inhibition of TASK and possibly other (e.g., BK C a ) potassium channels which leads to membrane depolarization, voltage-gated Ca-entry, and neurosecretion. Here, we investigate the effects of pharmacological inhibitors on TASK channel activity and [Ca 2+ ] i -signaling in isolated neonatal rat type-1 cells. PK-THPP inhibited TASK channel activity in cell attached patches by up to 90% (at 400 nmol/L). A1899 inhibited TASK channel activity by 35% at 400 nmol/L. PK-THPP, A1899 and Ml 365 all evoked a rapid increase in type-1 cell [Ca 2+ ] i . These [Ca 2+ ] i responses were abolished in Ca 2+ -free solution and greatly attenuated by Ni 2+ (2 mM) suggesting that depolarization and voltage-gated Ca 2+ -entry mediated the rise in [Ca 2+ ] i. Doxapram (50 μmol/L), a respiratory stimulant, also inhibited type-1 cell TASK channel activity and increased [Ca 2+ ] i. . We also tested the effects of combined inhibition of BK C a and TASK channels. TEA (5 mmol/L) slightly increased [Ca 2+ ] i in the presence of PK-THPP and A1899. Paxilline (300 nM) and iberiotoxin (50 nmol/L) also slightly increased [Ca 2+ ] i in the presence of A1899 but not in the presence of PK-THPP. In general [Ca 2+ ] i responses to TASK inhibitors, alone or in combination with BK C a inhibitors, were smaller than the [Ca 2+ ] i responses evoked by hypoxia. These data confirm that TASK channel inhibition is capable of evoking membrane depolarization and robust voltage-gated Ca 2+ -entry but suggest that this, even with concomitant inhibition of BK C a channels, may be insufficient to account fully for the [Ca 2+ ] i -response to hypoxia., (© 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

Objective: To compare the effects of alfaxalone and propofol, with and without acepromazine and butorphanol followed by doxapram, on laryngeal motion and quality of laryngeal examination in dogs., Study Design: Randomized, crossover, blinded study., Animals: Ten female Beagle dogs, aged 11-13 months and weighing 7.2-8.6 kg., Methods: The dogs were administered four intravenous (IV) treatments: alfaxalone (ALF), alfaxalone+acepromazine and butorphanol (ALF-AB), propofol (PRO) and propofol+AB (PRO-AB). AB doses were standardized. Dogs were anesthetized 5 minutes later by administration of alfaxalone or propofol IV to effect. Arytenoid motion during maximal inspiration and expiration was captured on video before and after IV doxapram (0.25 mg kg -1 ). The change in rima glottidis surface area (RGSA) was calculated to measure arytenoid motion. An investigator blinded to the treatment scored laryngeal examination quality., Results: A 20% increase in RGSA was the minimal arytenoid motion that was detectable. RGSA was significantly less in ALF before doxapram compared with all other treatments. A <20% increase in RGSA was measured in eight of 10 dogs in PRO and in all dogs in ALF before doxapram. After doxapram, RGSA was significantly increased for PRO and ALF; however, 20% of dogs in PRO and 50% of dogs in ALF still had <20% increase in RGSA. A <20% increase in RGSA was measured in five of 10 dogs in PRO-AB and ALF-AB before doxapram. All dogs in PRO-AB and ALF-AB with <20% increase in RGSA before doxapram had ≥20% increase in RGSA after doxapram. Examination quality was significantly better in PRO-AB and ALF-AB., Conclusions and Clinical Relevance: The use of acepromazine and butorphanol improved the quality of laryngeal examination. Any negative impact on arytenoid motion caused by these premedications was overcome with doxapram. Using either propofol or alfaxalone alone is not recommended for the evaluation of arytenoid motion., (Copyright © 2018 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Earlier, we reported that three Food and Drug Administration-approved drugs, trifluoperazine (TFP; an antipsychotic), amoxapine (AXPN; an antidepressant), and doxapram (DXP; a breathing stimulant), identified from an in vitro murine macrophage cytotoxicity screen, provided mice with 40 to 60% protection against pneumonic plague when administered at the time of infection for 1 to 3 days. In the present study, the therapeutic potential of these drugs against pneumonic plague in mice was further evaluated when they were administered at up to 48 h postinfection. While the efficacy of TFP was somewhat diminished as treatment was delayed to 24 h, the protection of mice with AXPN and DXP increased as treatment was progressively delayed to 24 h. At 48 h postinfection, these drugs provided the animals with significant protection (up to 100%) against challenge with the agent of pneumonic or bubonic plague when they were administered in combination with levofloxacin. Likewise, when they were used in combination with vancomycin, all three drugs provided mice with 80 to 100% protection from fatal oral Clostridium difficile infection when they were administered at 24 h postinfection. Furthermore, AXPN provided 40 to 60% protection against respiratory infection with Klebsiella pneumoniae when it was administered at the time of infection or at 24 h postinfection. Using the same in vitro cytotoxicity assay, we identified an additional 76/780 nonantibiotic drugs effective against K. pneumoniae For Acinetobacter baumannii , 121 nonantibiotic drugs were identified to inhibit bacterium-induced cytotoxicity in murine macrophages. Of these 121 drugs, 13 inhibited the macrophage cytotoxicity induced by two additional multiple-antibiotic-resistant strains. Six of these drugs decreased the intracellular survival of all three A. baumannii strains in macrophages. These results provided further evidence of the broad applicability and utilization of drug repurposing screening to identify new therapeutics to combat multidrug-resistant pathogens of public health concern., (Copyright © 2017 American Society for Microbiology.)

Considering the conserved nature of synaptic physiology among vertebrates, we tested the effects of three psychotropics (diazepam, doxapram, and nicotine) on Microsternarchus cf. bilineatus, measuring 10 parameters associated to the electric organ discharges rhythm and waveform before and after the administration of each drug and a control group. There were statistically significant differences (p < 0.005) among all the experimental groups, F (70, 22619.25) = 77.7, between the two experimental phases within their respective drug treatment, F (80, 24604.51) = 16.0, and among the six experimental hours within their respective phases and groups, F (320, 37124.15) = 4.1. We observed a common general trend of reduction in the electric organ's (EO) firing rate, regardless of the expected stimulant or depressor effect of the drugs on the central nervous system (CNS). The intensity of the response changed with the treatment. The observed changes in the fishes' behavior may be a result of the drugs' direct action on the CNS or a combination of this with systemic effects of each substance tested, also in the EO.

Background: Drug effect evaluation is often based on subjective interpretation of a selection of patient data. Continuous analyses of high frequency patient monitor data are a valuable source to measuring drug effects. However, these have not yet been fully explored in clinical care. We aim to evaluate the usefulness and applicability of high frequency physiological data for analyses of pharmacotherapy., Methods: As a proof of principle, the effects of doxapram, a respiratory stimulant, on the oxygenation in preterm infants were studied. Second-to-second physiological data were collected from 12 hours before until 36 hours after start of doxapram loading dose plus continuous maintenance dose in seven preterm infants. Besides physiological data, plasma concentrations of doxapram and keto-doxapram were measured., Results: Arterial oxygen saturation (SpO2) increased after the start of doxapram treatment alongside an increase in heart rate. The respiratory rate remained unaffected. The number of saturation dips and the time below a saturation of 80%, as well as the area under the 80%-saturation-time curve (AUC), were significantly lowered after the start of doxapram. The AUC under 90% saturation also significantly improved after start of doxapram. Plasma concentrations of doxapram and keto-doxapram were measured., Conclusion: Using high-frequency monitoring data, we showed the detailed effects over time of pharmacotherapy. We could objectively determine the respiratory condition and the effects of doxapram treatment in preterm infants. This type of analysis might help to develop individualized drug treatments with tailored dose adjustments based on a closed-loop algorithm., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Objectives: To determine whether CX1942 reverses respiratory depression in etorphine-immobilized goats, and to compare its effects with those of doxapram hydrochloride., Study Design: A prospective, crossover experimental trial conducted at 1753 m.a.s.l., Animals: Eight adult female Boer goats (Capra hircus) with a mean ± standard deviation mass of 27.1 ± 1.6 kg., Methods: Following immobilization with 0.1 mg kg(-1) etorphine, goats received one of doxapram, CX1942 or sterile water intravenously, in random order in three trials. Respiratory rate, ventilation and tidal volume were measured continuously. Arterial blood samples for the determination of PaO2 , PaCO2 , pH and SaO2 were taken 2 minutes before and then at 5 minute intervals after drug administration for 25 minutes., Results: Doxapram corrected etorphine-induced respiratory depression but also led to arousal and hyperventilation at 2 minutes after its administration, as indicated by the low PaCO2 (27.8 ± 4.5 mmHg) and ventilation of 5.32 ± 5.24 L minute(-1) above pre-immobilization values. CX1942 improved respiratory parameters and corrected etorphine's hypoxaemic effects more gradually than did doxapram, with a more sustained improvement in PaO2 and SaO2 in comparison with the control trial., Conclusions: CX1942 attenuated opioid-induced respiratory depression and corrected the hypoxaemic effects of etorphine in immobilized goats., Clinical Relevance: Ampakines potentially offer advantages over doxapram, a conventional treatment, in reversing etorphine-induced respiratory depression without causing unwanted side effects, particularly arousal, in immobilized animals., (© 2016 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.)

The present study was undertaken to investigate whether doxapram, a blocker of tandem pore K(+) (TASK-1/-3) channels, is a useful tool for recovery from morphine-induced ventilatory disturbances. Spontaneous ventilation and the hind leg withdrawal response against noxious thermal stimulation were recorded simultaneously in anesthetized rats. Morphine (1.0mg/kg, i.v.) decreased the minute volume resulting from depression of the ventilatory rate and tracheal airflow. Concomitantly, it prolonged the latency of withdrawal response against the thermal stimulation. Subsequent intravenous injection of doxapram recovered the morphine-induced ventilatory depression. This effect of doxapram declined rapidly after a single injection (1.0-3.0mg/kg, i.v.) but persisted with a continuous infusion (0.33mg/kg/min). Neither single injection nor continuous infusion of doxapram had any detectable effect on the analgesic potency of morphine. The central respiratory activity was recorded from the phrenic nerve in anesthetized, vagotomized, paralyzed and artificially ventilated rats. Morphine (3.0mg/kg, i.v.) induced respiratory depression, characterized by a prolonged plateau-like inspiratory discharge (apneustic discharge) in the phrenic nerve. Doxapram (10mg/kg, i.v.) restored the morphine-induced apneustic discharge to an augmenting inspiratory discharge. This study demonstrated that doxapram counteracted morphine-induced respiratory depression by stimulating the central respiratory network without compromising morphine antinociception. These results support the clinical use of doxapram for amelioration of ventilatory disturbances in patients treated with opioids., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Antibiotic resistance in medically relevant bacterial pathogens, coupled with a paucity of novel antimicrobial discoveries, represents a pressing global crisis. Traditional drug discovery is an inefficient and costly process; however, systematic screening of Food and Drug Administration (FDA)-approved therapeutics for other indications in humans offers a rapid alternative approach. In this study, we screened a library of 780 FDA-approved drugs to identify molecules that rendered RAW 264.7 murine macrophages resistant to cytotoxicity induced by the highly virulent Yersinia pestis CO92 strain. Of these compounds, we identified 94 not classified as antibiotics as being effective at preventing Y. pestis-induced cytotoxicity. A total of 17 prioritized drugs, based on efficacy in in vitro screens, were chosen for further evaluation in a murine model of pneumonic plague to delineate if in vitro efficacy could be translated in vivo Three drugs, doxapram (DXP), amoxapine (AXPN), and trifluoperazine (TFP), increased animal survivability despite not exhibiting any direct bacteriostatic or bactericidal effect on Y. pestis and having no modulating effect on crucial Y. pestis virulence factors. These findings suggested that DXP, AXPN, and TFP may modulate host cell pathways necessary for disease pathogenesis. Finally, to further assess the broad applicability of drugs identified from in vitro screens, the therapeutic potential of TFP, the most efficacious drug in vivo, was evaluated in murine models of Salmonella enterica serovar Typhimurium and Clostridium difficile infections. In both models, TFP treatment resulted in increased survivability of infected animals. Taken together, these results demonstrate the broad applicability and potential use of nonantibiotic FDA-approved drugs to combat respiratory and gastrointestinal bacterial pathogens., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

To determine the costs of pulmonary ventilation without imposing severe oxygen limitations or acidosis that normally accompany exposures to hypoxia or hypercapnia, we opted to pharmacologically stimulate ventilation with doxapram (5 and 10 mg kg(-1)) in alligators. Doxapram is used clinically to alleviate ventilatory depression in response to anaesthesia and acts primarily on the peripheral oxygen-sensitive chemoreceptors. Using this approach, we investigated the hypothesis that pulmonary ventilation is relatively modest in comparison to resting metabolic rate in crocodilians and equipped seven juvenile alligators with masks for concurrent determination of ventilation and oxygen uptake. Doxapram elicited a dose-dependent and up to fourfold rise in ventilation, primarily by increasing ventilatory frequency. The accompanying rise in oxygen uptake was very small; ventilation in resting animals constitutes no more than 5% of resting metabolic rate. The conclusion that pulmonary ventilation is energetically cheap is consistent with earlier studies on alligators where ventilation was stimulated by hypoxia or hypercapnia., (© 2016. Published by The Company of Biologists Ltd.)

Compounds PKTHPP (1-{1-[6-(biphenyl-4-ylcarbonyl)-5,6,7,8-tetrahydropyrido[4,3-d]-pyrimidin-4-yl]piperidin-4-yl}propan-1-one), A1899 (2''-[(4-methoxybenzoylamino)methyl]biphenyl-2-carboxylic acid 2,4-difluorobenzylamide), and doxapram inhibit TASK-1 (KCNK3) and TASK-3 (KCNK9) tandem pore (K2P) potassium channel function and stimulate breathing. To better understand the molecular mechanism(s) of action of these drugs, we undertook studies to identify amino acid residues in the TASK-3 protein that mediate this inhibition. Guided by homology modeling and molecular docking, we hypothesized that PKTHPP and A1899 bind in the TASK-3 intracellular pore. To test our hypothesis, we mutated each residue in or near the predicted PKTHPP and A1899 binding site (residues 118-128 and 228-248), individually, to a negatively charged aspartate. We quantified each mutation's effect on TASK-3 potassium channel concentration response to PKTHPP. Studies were conducted on TASK-3 transiently expressed in Fischer rat thyroid epithelial monolayers; channel function was measured in an Ussing chamber. TASK-3 pore mutations at residues 122 (L122D, E, or K) and 236 (G236D) caused the IC50 of PKTHPP to increase more than 1000-fold. TASK-3 mutants L122D, G236D, L239D, and V242D were resistant to block by PKTHPP, A1899, and doxapram. Our data are consistent with a model in which breathing stimulant compounds PKTHPP, A1899, and doxapram inhibit TASK-3 function by binding at a common site within the channel intracellular pore region, although binding outside the channel pore cannot yet be excluded., (Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.)

Objective: To compare the agreement, repeatability and trending ability of transpulmonary thermodilution (TPTD) and pulmonary artery thermodilution (PATD) cardiac output (Q˙t) measurements in unsedated newborn calves., Study Design: Prospective experimental trial., Animals: Eight newborn calves weighing a median (range) of 53 (46-59) kg., Methods: Pulmonary and femoral artery thermodilution catheters were placed under local anaesthesia. A total of 382 PATD and TPTD Q˙t measurements were performed simultaneously. Cardiac output was influenced by intravenous doxapram and theophylline in a randomized crossover fashion. Bland-Altman analysis for multiple comparisons, concordance and polar plots were used to assess TPTD against PATD., Results: Median (range) cardiac index values measured with PATD and TPTD were 197 mL kg(-1) minute(-1) (74-335 mL kg(-1) minute(-1)) and 196 mL kg(-1) minute(-1) (59-395 mL kg(-1) minute(-1)), respec-tively. A small mean bias of -3 mL kg(-1) minute(-1) with limits of agreement (LOA) of -64 to 58 mL kg(-1) minute(-1) and a percentage error of 31% were found. Eighty-two mean values were calculated. This reduced the LOA to -50 to 41 mL kg(-1) minute(-1) with a similar small bias and a percentage error of 23%. Mean TPTD tracked changes in Q˙t compared with mean PATD with 90% concordance, a mean polar angle of 6° and radial LOA of 43°, indicating marginal trending ability. Keeping the femoral artery catheter patent and obtaining acceptable measurements were very challenging because the calves were not used to being restrained. Calf movement had less influence on PATD., Conclusions and Clinical Relevance: We recommend that PATD remains the reference method to measure Q˙t in unsedated newborn calves. However, the robust results of the evaluation of the less invasive TPTD technique warrants further evaluation taking into account the difficulties reported in this study., (© 2015 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.)

We fitted two blue wildebeest (Connochaetes taurinus) with modified versions of the Equivital™ EQ02 wireless monitoring system to evaluate if the device could accurately measure heart rate and respiration rate in this species whilst anaesthetized as well as whilst fully conscious in captivity. Whilst under anaesthesia, we monitored each animal's heart rate and respiration rate using the Equivital™ biotelemetry belt, a Cardell(®) veterinary monitor and manual measurements. The animals were also administered doxapram hydrochloride (Dopram(®) ) and adrenaline intravenously at different times to stimulate changes in respiration and heart rate, respectively. Once 30 minutes of monitoring was completed, we reversed the anaesthetic and left the animals in captivity for 24 hours whilst wearing the Equivital™ belts. After 24 hr, we repeated the anaesthesia and monitoring as well as the administration of the doxapram hydrochloride and adrenaline. Intraclass Correlation Coefficients (ICC) calculated between all three monitoring methods showed moderate to excellent agreements for heart rate on both days (ICC: 0.73-0.98). ICCs calculated between the three methods for respiration rate showed good to excellent agreement between the Equivital belt and the other two methods (0.82-0.92) with the exception of occasions when only poor to fair agreements were found between the Cardell(®) measurements and manual measurements. Heart rate and respiration rate were also found to increase with motion while animals were in captivity. The results indicate that a modified version of the Equivital™ EQ02 system can be used as a potential biotelemetry device for measuring heart and respiration rate in captive blue wildebeest., (© 2015 Wiley Periodicals, Inc.)

Panic disorder (PD) is characterized by anticipatory anxiety and panic, both causing physiological arousal. We investigated the differential responses between anticipatory anxiety and panic in PD and healthy controls (HC). Subjects (15 PD and 30 HC) received an injection of a respiratory stimulant, doxapram, with a high rate of producing panic attacks in PD patients, or an injection of saline. PD subjects had significantly higher scores in anxiety and panic symptoms during both conditions. Analysis of heart rate variability (HRV) indices showed higher sympathetic activity (LF) during anticipatory anxiety and panic states, an increase in the ratio of LF/HF during the anticipatory and panic states and a decrease in parasympathetic (HF) component in PD patients. During doxapram PD subjects increased their LF/HF ratio while HC had a reduction in LF/HF. Parasympathetic component of HRV was lower during anticipatory anxiety in PD. In general, PD showed greater sympathetic and psychological responses related to anxiety and sensations of dyspnea, reduced parasympathetic responses during anticipatory and panic states, but no differences in respiratory response. This confirms previous studies showing that PD patients do not have an intrinsic respiratory abnormality (either heightened or dysregulated) at the level of the brain stem but rather an exaggerated fear response., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Aim: The aim of this study was to measure the brain activity of preterm infants treated with caffeine citrate and doxapram for preterm apnoea, using amplitude-integrated electroencephalography (aEEG), to identify any adverse effects on cerebral function., Methods: We analysed the aEEG tracings of 13 preterm infants <30 weeks of gestation before, during and after doxapram treatment, with regard to background activity (percentages of continuous and discontinuous patterns), occurrence of sleep-wake cycling and appearance of electrographic seizure activity. They were also compared with 61 controls without doxapram treatment., Results: During doxapram treatment, aEEG tracings showed an increase in continuous background activity (19 ± 30% before treatment, 38 ± 35% during treatment) and a decrease in discontinuous patterns. In addition, they showed more frequent electrographic seizure activity (0% before treatment, 15 ± 37% during treatment) and less frequent sleep-wake cycling (92 ± 27% before treatment, 85 ± 37% during treatment) could be observed. These results were confirmed when compared to the control group., Conclusion: Doxapram treatment influences aEEG in preterm infants, showing higher percentages of continuous activity as well as more electrographic seizure activity and less sleep-wake cycling. It should, therefore, be used with caution in very preterm infants., (©2014 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.)

Doxapram is the only dedicated respiratory stimulant used to aid recovery of breathing after major surgery. Doxapram acts on peripheral chemoreceptors and although the central action of doxapram has been suggested, its detailed neuronal mechanism is unknown. We assessed doxapram-induced changes in spontaneous cervical nerve (C4) inspiratory activity and the firing of action potentials in pre-inspiratory and inspiratory neurones in the medulla. Experiments were performed in neonatal rat brainstem-spinal cord preparations, which can produce respiratory rhythm for several hours under in vitro conditions. Doxapram application (for 15 min) increased the frequency and amplitude of C4 activity dose-dependently. Doxapram induced changes in the electrophysiological properties of pre-inspiratory and inspiratory neurones. Our results suggest that respiratory activity enhancement was likely to be induced via effects on the potassium channels of pre-inspiratory and inspiratory neurones and indicate the central actions of doxapram., (© 2014 The Association of Anaesthetists of Great Britain and Ireland.)

Study Objective: To compare the effects of aminophylline and doxapram on recovery, respiration, and bispectral index (BIS) values in patients after total intravenous anesthesia (TIVA) with propofol and remifentanil., Design: Prospective, randomized, blinded clinical trial., Setting: Operating room of a university hospital., Patients: 90 adult, ASA physical status 1 and 2 patients scheduled for elective laparoscopic vaginal hysterectomy., Interventions: TIVA was performed with the induction target of remifentanil 3 ng/mL and propofol 6 μg/mL, followed by the maintenance target of remifentanil 1-3 ng/mL and propofol 3-5 μg/mL at the effect site, and with BIS scores in 40-50 range. Patients were randomized to three groups to receive intravenous (IV) aminophylline 3 mg/kg (n = 30), IV doxapram 1 mg/kg (n = 30), or normal IV saline (control; n = 30)., Measurements and Main Results: After administration of the study drugs, return to spontaneous ventilation differed significantly among the three groups. The times to eye opening and hand squeezing on verbal command were similar. The time to extubation was shortened in both the doxapram and aminophylline groups (P < 0.05). Tidal volumes were increased in the doxapram group at 5-14 minutes and the aminophylline group at 5-12 minutes (P < 0.05). Respiratory rates were increased at 2 to 8 minutes and then showed a decrease at the 12 to 14-minute mark in both the doxapram and aminophylline groups (P < 0.05). No difference was noted between the two groups. BIS values were increased in both the doxapram and aminophylline groups at 4-10 minutes (P < 0.05). Heart rates were increased in the doxapram group for the first 8 minutes and at 1-2 minutes in the aminophylline group (P < 0.05)., Conclusion: Aminophylline 3 mg/kg or doxapram 1 mg/kg shortened the time to spontaneous ventilation and improved early recovery from TIVA without appreciable side effects. The more rapid emergence correlates with higher BIS values when compared with the saline control group. The arousal and respiratory effects of aminophylline were comparable to those of doxapram., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: TASK-1 and TASK-3 tandem pore potassium channel subunits provide a constitutive acidic pH- and hypoxia-inhibited potassium conductance. TASK channels are expressed in a number of tissues involved in regulation of breathing, and the TASK-1/TASK-3 heterodimer provides the predominant hypoxia-sensitive potassium conductance in carotid body type 1 glomus chemosensing cells. The carotid bodies have an important role in regulation of breathing. Doxapram is a potent TASK-1 and TASK-3 potassium channel antagonist and a carotid body and breathing stimulant. PK-THPP and A1899 are potent and selective TASK-1 and TASK-3 antagonists. I hypothesized PK-THPP and A1899 are, like doxapram, breathing stimulants., Methods: I studied rat TASK-3 potassium channel function by Ussing chamber using Fischer rat thyroid monolayers. To quantify breathing effects, I studied male Sprague-Dawley rats spontaneously breathing 1.5% isoflurane in room air by noninvasive plethysmography and by arterial blood gas analysis., Results: PK-THPP, A1899, and doxapram inhibit rat TASK-3 potassium channel function with IC50s of 42 nM (33-52), 1.6 μM (0.8-3.3), and 22 μM (18-28) (n = 4-6; 95% confidence limits). IV PK-THPP, A1899, and doxapram stimulated breathing by plethysmography with a peak change in minute ventilation relative to baseline of 84% ± 19% and 226% ± 56% (for PK-THPP at 0.5 and 5 mg/kg; mean ± SEM; n = 3-4; P < 0.05 and P < 0.001, respectively, relative to vehicle); 46% ± 2% and 236% ± 48% (for A1899 at 5 and 25 mg/kg; n = 3-4; P > 0.05 and P < 0.001, respectively); 103% ± 20% (for doxapram at 25 mg/kg; n = 4), and 33% ± 9% (for dimethylsulfoxide vehicle at 1 mL/kg; n = 4). PK-THPP and A1899, unlike doxapram, induced a profound and lasting respiratory alkalosis by arterial blood gas analysis. Thirty minutes after IV drug administration, I observed an arterial pH and carbon dioxide partial pressure of 7.62 ± 0.02 and 23 ± 0.8 mm Hg (for PK-THPP after 5 mg/kg; n = 4; P < 0.001 for both relative to vehicle), 7.49 ± 0.02 and 31 ± 2 mm Hg (for A1899 at 25 mg/kg; n = 6; P < 0.05 and 0.001, respectively), 7.43 ± 0.03 and 39 ± 4 mm Hg (for doxapram after 25 mg/kg; n = 4; P > 0.05 for both), and 7.38 ± 0.03 and 48 ± 4 mm Hg (for dimethylsulfoxide vehicle after 1 mL/kg; n = 3)., Conclusions: PK-THPP and A1899 are potent rat TASK-3 antagonists and effective breathing stimulants. PK-THPP and A1899 effects on breathing were of greater magnitude and/or duration relative to that of doxapram. PK-THPP and A1899 or related compounds may have therapeutic potential for treating breathing disorders.

Objectives: The benefits of spontaneous breathing over muscle paralysis have been proven mainly in mild lung injury; no one has yet evaluated the effects of spontaneous breathing in severe lung injury. We investigated the effects of spontaneous breathing in two different severities of lung injury compared with muscle paralysis., Design: Prospective, randomized, animal study., Setting: University animal research laboratory., Subjects: Twenty-eight New Zealand white rabbits., Interventions: Rabbits were randomly divided into the mild lung injury (surfactant depletion) group or severe lung injury (surfactant depletion followed by injurious mechanical ventilation) group and ventilated with 4-hr low tidal volume ventilation with spontaneous breathing or without spontaneous breathing (prevented by a neuromuscular blocking agent). Inspiratory pressure was adjusted to control tidal volume to 5-7 mL/kg, maintaining a plateau pressure less than 30 cm H2O. Dynamic CT was used to evaluate changes in lung aeration and the regional distribution of tidal volume., Measurements and Results: In mild lung injury, spontaneous breathing improved oxygenation and lung aeration by redistribution of tidal volume to dependent lung regions. However, in severe lung injury, spontaneous breathing caused a significant increase in atelectasis with cyclic collapse. Because of the severity of lung injury, this group had higher plateau pressure and more excessive spontaneous breathing effort, resulting in the highest transpulmonary pressure and the highest driving pressure. Although no improvements in lung aeration were observed, muscle paralysis with severe lung injury resulted in better oxygenation, more even tidal ventilation, and less histological lung injury., Conclusions: In animals with mild lung injury, spontaneous breathing was beneficial to lung recruitment; however, in animals with severe lung injury, spontaneous breathing could worsen lung injury, and muscle paralysis might be more protective for injured lungs by preventing injuriously high transpulmonary pressure and high driving pressure.

A number of drugs have been used to treat asphyxia in new-born calves and the aim of the current study was to investigate the effect of commonly-used stimulant drugs on ventilation, arterial blood gas and acid base variables. A group (n=18) of new-born (3-15 h old) calves were treated in a randomised sequence with doxapram (40 mg, IV), lobeline (5mg, IV) or prethcamide (5 mL, consisting of 375 mg crotethamide and 375 mg cropropamide, buccally). Blood and spirometric measurements, using an ultrasonic spirometer, were collected prior to and 1, 5, 15, 30, 60, 90 min after administration of each drug. Doxapram caused a significant increase in the respiratory rate, peak inspiratory and expiratory flow and minute volume (V(min)) during the 90-min post-treatment study period, although maximum values occurred 1 min after treatment. The V(min) increased from 13.8 ± 5.0 L to 28.5 ± 12.3 L. Prethcamide, but not lobeline, also caused significant increases in inspiratory and expiratory volumes. The effects of doxapram on ventilation were accompanied by an increase in arterial partial pressure of oxygen (P(a)O(2)) (77.7 ± 18.8 mm Hg to 93.2 ± 23.7 mm Hg), a decrease in arterial partial pressure of carbon dioxide (P(a)CO(2)) (42.6 ± 4.9 mm Hg to 33.1 ± 6.6mm Hg), a significant increase in pH and a decrease in bicarbonate concentration and base excess 1 min after treatment. Prethcamide caused a gradual increase in P(a)O(2) and decrease in P(a)CO(2) over 90 min, whereas lobeline had no measurable effect on the investigated variables. Of the three treatments, only doxapram had a distinct stimulatory effect on respiration in healthy neonatal calves and may therefore be useful in the treatment of calf asphyxia., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Introduction: The Safety Pharmacology ICH S7A guidelines mandate the preclinical evaluation of drug effects on respiratory function. Chronic measurements of potential drug effects are commonly performed in rodents due to lack of a viable alternative in large animals. Presently, although the value and validity of these standard methods cannot be refuted, each method presents inherent limitations; such as the introduction of restraint stress (e.g. head-out rodent plethysmography and the pneumotachograph-equipped dog face mask), or sensitivity issues (e.g. whole body plethysmography). Since these approaches may limit the number of time points tested or affect respiratory parameters, new and accurate methods are needed for assessing respiratory function in conscious, freely moving animals., Methods: We evaluated a new surgically implanted telemetry device, which adds an impedance sensor for the chronic measurement of respiratory parameters to the standard device used for safety pharmacology cardiovascular studies. The feasibility of the implantable device was assessed based on concordance of respiratory data with pneumotachograph-recorded parameters in conscious Beagle dogs following intravenous administration of a positive control (4 mg/kg doxapram)., Results: Linear regression analysis of data collected under restrained conditions showed a high correlation (R(2) 0.95) between impedance-derived respiratory parameters (tidal volume and respiratory frequency) and direct measurements of respiration via pneumotachograph. The correlation was reproduced when animals were challenged under the same dosing regimen. Volume changes similar to those obtained during the restrained collection were observed during the ambulatory collection following doxapram administration. Calibration of impedance-based values was adequate using both individual and population-based baseline conversion factors, both approximating actual mean respiratory variables collected with the pneumotachograph., Discussion: The benefit of this model is the accurate, continuous measurement of respiratory endpoints in restrained, as well as ambulatory settings. Assessment of multiple physiological parameters collected concurrently and the use of population-based calibrations may enable the maximization of resources and shortened timelines in drug development., (2010 Elsevier Inc. All rights reserved.)

We studied the effects of the ventilatory stimulant doxapram to test the hypothesis that chronic hypoxia increases the translation of carotid body afferent input into ventilatory motor efferent output by the central nervous system. Chronic hypoxia (inspired Po(2) = 70 Torr, 2 days) significantly increased the ventilatory response to an intravenous infusion of a high dose of doxapram in conscious, unrestrained rats breathing normoxic or hypoxic gas. The in vitro carotid body response to hypoxia increased with chronic hypoxia, but the response was not increased with a high dose of doxapram. Similarly, the phrenic nerve response to doxapram in anesthetized rats with carotid bodies denervated did not change with 7 days of chronic hypoxia. The results support the hypothesis that chronic hypoxia causes plasticity in the central component of the carotid chemoreceptor ventilatory reflex, which increases the hypoxic ventilatory response. We conclude that doxapram provides a promising tool to study the time course of changes in the central gain of the hypoxic ventilatory response during chronic hypoxia in awake animals and humans.

This study tested whether the glial cells are involved in the exciting effects of doxapram on brainstem slice in vitro. Experiments were performed in brainstem slice preparations from neonatal rats. The medial area of nucleus retrofacialis (mNRF) and the hypoglossal nerve (XII nerve) were contained in the preparations. The slices were perfused with modified Kreb's solution (MKS), and the rhythmical respiratory discharge activity (RRDA) was simultaneously recorded from the XII nerve by using suction electrodes, including the discharge time course of inspiratory (Ti), expiratory (Te), respiratory cycle (RC), and integrity amplitude of inspiratory discharge (IA). After applying of doxapram (5 microM) to the MKS for 10 min, Ti and IA increased significantly (85.0 +/- 25.0%, 13.2 +/- 2.5%, respectively, P < 0.05), the Te and the RC decreased significantly (19.0 +/- 1.4%, 12.8 +/- 1.4%, respectively, P < 0.05) when compared with control group. When the methionine sulfoximine (MS, 10 microM), a blockage of glutamine synthetase, was applied, all the exciting effects of doxapram on RRDA were reversed. After the glutamine (20 microM) was applied to the MKS for 10 min, the exciting effects were revealed again. Our results suggest that the normal metabolism of glial cells takes a key role in the modification of the RRDA in the slices. In conclusion, glial cells are involved in the exciting effects of doxapram on brainstem slice in vitro.

Introduction: Assessing the effects of new chemical entities on respiratory function in animal models is an essential component of preclinical drug safety evaluation. Methods currently available for measuring ventilatory parameters in conscious dogs generally utilize a plethysmograph chamber or a face mask equipped with a pneumotachograph attached to the snout of the animal. These methods require restraint and allow for only short, periodic measurements. Because of these limitations, respiratory inductive plethysmography (RIP) was evaluated as a possible new methodology that will allow for continuous monitoring of respiratory parameters in non-restrained dogs for extended periods of time., Methods: Straps containing inductive coils were placed around the thorax and abdomen to measure thoracic and abdominal excursions. The straps were contained within a protective jacket that was placed on the dogs and the electrical signals from the inductive coils were transmitted by telemetry to a receiver. The data were acquired and analyzed using the Vivometrics(R) LifeShirt(R) PreClinical System. Because postural changes can alter tidal volume measurements using RIP, the jacket also contained an accelerometer that was used to record postural changes during ventilatory measurements., Results: Measurement of ventilatory parameters in dogs following manual placement in different positions (e.g., standing, sitting, lateral recumbent) or during the different postures in non-restrained dogs demonstrated that changes in posture had only a minimal influence (

Respiratory depression is a common side effect when opioids are used to immobilize wildlife. Serotonergic ligands have the potential to reverse opioid-induced respiratory depression. We examined whether any of three serotonergic ligands could reverse this depression in etorphine-immobilized (0.07 mg/kg) impala (Aepyceros melampus). The study took place in September-December 2007. Impala received intravenous injections of metoclopramide (10 mg/kg, n=6), buspirone (0.05 mg/kg, n=8), pimozide (1 mg/kg, n=8), doxapram (1 mg/kg, n=6), and control solutions on separate occasions. During the immobilization, partial pressures of oxygen (PaO(2), mmHg) and carbon dioxide (PaCO(2), mmHg), respiratory rate (breaths/min), ventilation (l/min), peripheral O(2) saturation (%), tidal volume (l), and respiratory exchange ratio were measured before and after injection of the experimental drugs. Etorphine immobilization caused respiratory depression and hypoxia (mean+/-SD, PaCO(2)=51+/-2 mmHg, PaO(2)=40+/-3 mmHg). Metoclopramide and buspirone, but not pimozide, attenuated the hypoxic effects of etorphine; 3 min after injection, metoclopramide increased the PaO(2) by 7.5+/-6.3 mmHg and buspirone by 6+/-6.6 mmHg (F=3.9, P=0.02). These effects were similar to those of doxapram (8+/-7 mmHg, F=3.9; P>0.05). Neither metoclopramide nor buspirone significantly increased ventilation, but they increased PaO(2) by significantly improving the alveolar-arterial oxygen partial pressure gradient (A-a gradient, F=1.4, P<0.05), indicating improved oxygen diffusion. Metoclopramide and buspirone transiently improved blood oxygenation of opioid-immobilized impala, probably by improving ventilation-perfusion ratios, without reversing catatonic immobilization.

Respiratory stimulants are widely used in asphyxic neonatal calves despite a lack of data about their effectiveness and indications of possible side effects. The effect of doxapram and theophylline on respiratory, cardiovascular, and acid-base variables was investigated in 10 healthy neonatal calves (Bos Taurus). A venous, a peripheral arterial, and a pulmonary arterial catheter were placed, and central venous, pulmonary, and systemic blood pressures and cardiac output were measured using thermodilution technique. Doxapram, but not theophylline, led to an immediate increase in respiratory rate (P

Objective: To investigate the effects of doxapram on the respiratory rhythmical discharge activity (RRDA) in the brainstem slices of neonatal rats., Methods: Thirty neonatal SD rats (of either sex, 0-3 days old) were randomly divided into 6 equal groups (groups I-VI), and the brainstem slices which contained the medial region of the nucleus retrofacialis (mNRF) were prepared. All the slices were perfused with modified Kreb's solution (MKS), and in group I (control group), the slices were perfused with MKS only; in groups II to IV, the slices were perfused with doxapram in MKS continuously at the concentrations of 2, 5, and 10 micromol/L, respectively; in groups V and VI, the slices were perfused with 20 micromol/L propofol and 20 micromol/L propofol plus 5 micromol/L doxapram, respectively. The RRDA in the hypoglossal nerve was recorded by suction electrode. The discharge time course of the inspiratory (TI), expiratory (TE), respiratory cycle (RC) and integral amplitude of the inspiratory discharge (IA) were recorded at 1, 3, 5, 10, 15, and 30 min after the application of the drugs., Results: The hypoglossal nerve in groups I, II and VI showed no significant changes of RRDA in the entire course of the experiment (P>0.05). In groups III and IV, the TI, IA increased and TE decreased significantly 5 min after doxapram application (P<0.05), and the RC was shortened only at 10 min. In group V, the TI and IA decreased and the RC and TE increased significantly after the drug application (P<0.05)., Conclusion: Doxapram (>5 micromol/L ) can directly stimulate the RRDA and prevent propofol-induced inhibitory effects in the brainstem slice of neonatal rats, and the effects are mediated by its actions upon the inspiratory neurons in the mNRF.

Ethanol is now considered the most common human teratogen. Educational campaigns have not reduced the incidence of ethanol-mediated teratogenesis, leading to a growing interest in the development of therapeutic prevention or mitigation strategies. On the basis of the observation that maternal ethanol consumption reduces maternal and fetal pH, we hypothesized that a pH-sensitive pathway involving the TWIK-related acid-sensitive potassium channels (TASKs) is implicated in ethanol-induced injury to the fetal cerebellum, one of the most sensitive targets of prenatal ethanol exposure. Pregnant ewes were intravenously infused with ethanol (258+/-10 mg/dl peak blood ethanol concentration) or saline in a "3 days/wk binge" pattern throughout the third trimester. Quantitative stereological analysis demonstrated that ethanol resulted in a 45% reduction in the total number of fetal cerebellar Purkinje cells, the cell type most sensitive to developmental ethanol exposure. Extracellular pH manipulation to create the same degree and pattern of pH fall caused by ethanol (manipulations large enough to inhibit TASK 1 channels), resulted in a 24% decrease in Purkinje cell number. We determined immunohistochemically that TASK 1 channels are expressed in Purkinje cells and that the TASK 3 isoform is expressed in granule cells of the ovine fetal cerebellum. Pharmacological blockade of both TASK 1 and TASK 3 channels simultaneous with ethanol effectively prevented any reduction in fetal cerebellar Purkinje cell number. These results demonstrate for the first time functional significance of fetal cerebellar two-pore domain pH-sensitive channels and establishes them as a potential therapeutic target for prevention of ethanol teratogenesis.

A number of life-threatening clinical disorders may be amenable to treatment with a drug that can stimulate respiratory drive. These include acute respiratory failure secondary to chronic obstructive pulmonary disease, post-anesthetic respiratory depression, and apnea of prematurity. Doxapram has been available for over forty years for the treatment of these conditions and it has a low side effect profile compared to other available agents. Generally though, the use of doxapram has been limited to these clinical niches involving patients in the intensive care, post-anesthesia care and neonatal intensive care units. Recent basic science studies have made considerable progress in understanding the molecular mechanism of doxapram's respiratory stimulant action. Although it is unlikely that doxapram will undergo a clinical renaissance based on this new understanding, it represents a significant advance in our knowledge of the control of breathing.

TWIK-related acid-sensitive K(+)-1 (TASK-1 [KCNK3]) and TASK-3 (KCNK9) are tandem pore (K(2P)) potassium (K) channel subunits expressed in carotid bodies and the brainstem. Acidic pH values and hypoxia inhibit TASK-1 and TASK-3 channel function, and halothane enhances this function. These channels have putative roles in ventilatory regulation and volatile anesthetic mechanisms. Doxapram stimulates ventilation through an effect on carotid bodies, and we hypothesized that stimulation might result from inhibition of TASK-1 or TASK-3 K channel function. To address this, we expressed TASK-1, TASK-3, TASK-1/TASK-3 heterodimeric, and TASK-1/TASK-3 chimeric K channels in Xenopus oocytes and studied the effects of doxapram on their function. Doxapram inhibited TASK-1 (half-maximal effective concentration [EC50], 410 nM), TASK-3 (EC50, 37 microM), and TASK-1/TASK-3 heterodimeric channel function (EC50, 9 microM). Chimera studies suggested that the carboxy terminus of TASK-1 is important for doxapram inhibition. Other K2P channels required significantly larger concentrations for inhibition. To test the role of TASK-1 and TASK-3 in halothane-induced immobility, the minimum alveolar anesthetic concentration for halothane was determined and found unchanged in rats receiving doxapram by IV infusion. Our data indicate that TASK-1 and TASK-3 do not play a role in mediating the immobility produced by halothane, although they are plausible molecular targets for the ventilatory effects of doxapram.

We determined the effects of doxapram on the major autonomic thermoregulatory responses in humans. Nine healthy volunteers were studied on 2 days: control and doxapram (IV infusion to a plasma concentration of 2.4 +/- 0.8, 2.5 +/- 0.9, and 2.6 +/- 1.1 microg/mL at the sweating, vasoconstriction, and shivering thresholds, respectively). Each day, skin and core temperatures were increased to provoke sweating, then reduced to elicit peripheral vasoconstriction and shivering. We determined the sweating, vasoconstriction, and shivering thresholds with compensation for changes in skin temperature. Data were analyzed with paired t-tests and presented as mean +/- sd; P < 0.05 was considered statistically significant. Doxapram did not change the sweating (control: 37.5 degrees +/- 0.4 degrees C, doxapram: 37.3 degrees +/- 0.4 degrees C; P = 0.290) or the vasoconstriction threshold (36.8 degrees +/- 0.7 degrees C versus 36.4 degrees +/- 0.5 degrees C; P = 0.110). However, it significantly reduced the shivering threshold from 36.2 degrees +/- 0.5 degrees C to 35.7 degrees +/- 0.7 degrees C (P = 0.012). No sedation or symptoms of panic were observed on either study day. The observed reduction in the shivering threshold explains the drug's efficacy for treatment of postoperative shivering; however, a reduction of only 0.5 degrees C is unlikely to markedly facilitate induction of therapeutic hypothermia as a sole drug.

Patients with chronic bronchial asthma show a depressed ventilatory response to hypoxia (DVH), but the underlying mechanism remains unclear. We tested whether DVH existed in ovalbumin (Ova)-treated guinea pigs, an established animal model of asthma. Twelve guinea pigs were exposed to Ova (1% in saline) or saline aerosol (control) for 5 min, 5 days/wk, for 2 wk. After completing aerosol exposure, the animals were anesthetized and exposed to systemic hypoxia. Ova treatment had no effects on animal body weight, baseline cardiorespiratory variables, or arterial blood O2 and CO2 tensions, but it attenuated the ventilatory response to hypoxia (10 breaths of pure N2) by 65% (P < 0.05). When the animals were subjected to intracarotid injections of sodium cyanide (20 microg) and doxapram (2 mg) to selectively stimulate carotid chemoreceptors, the ventilatory responses were reduced by 50% (P < 0.05) and 74% (P < 0.05), respectively. In contrast, Ova exposure failed to affect the ventilatory response to CO2 (7% CO2-21% O2-balance N2 for 5 min; P > 0.05). Furthermore, the apneic response evoked by stimulating bronchopulmonary C fibers (PCFs) with right atrial injection of capsaicin (5 microg) was markedly increased in the Ova-sensitized group (5.02 +/- 1.56 s), compared with the control group (1.82 +/- 0.45 s; P < 0.05). These results suggest that Ova sensitization induces a DVH in guinea pigs, which probably results from an attenuation of the carotid chemoreceptor-mediated ventilatory excitation and an enhancement of the PCF-mediated ventilatory inhibition.

Objective: Lack of appropriate top-down governance by frontal cortical regions over a hypersensitive amygdala-centered fear neurocircuitry has been hypothesized to be central in the pathophysiology of panic disorder. The aim of this study was to examine regional cerebral blood flow changes in response to anxiety/panic provocation in subjects with panic disorder and healthy comparison subjects., Method: Quantitative water method positron emission tomography was used to obtain brain images of five untreated subjects with panic disorder and five healthy comparison subjects before and during anxiogenic challenge with intravenous doxapram, an acute respiratory stimulant., Results: Baseline perfusion of the orbitofrontal cortex predicted panic attacks: lower perfusion was associated with heightened anxiety in response to doxapram challenge., Conclusions: The orbitofrontal cortex may be important in the regulation of responding to fear and is a potential area of aberrant functioning in panic disorder.

To determine if doxapram stimulates the carotid body through the same mechanism as hypoxia, we compared the effects of doxapram and hypoxia on isolated-perfused carotid bodies in rabbits. Doxapram stimulated the carotid body in a dose-dependent manner. In Ca(2+)-free solution, neither doxapram nor hypoxia stimulated the carotid body. Although, doxapram had an additive effect on the carotid body chemosensory response to hypercapnia, a synergistic effect was not observed. Also, we investigated the various K(+) channel activators on the response to doxapram and hypoxia: pinacidil and levcromakalim as ATP-sensitive K(+) channel activators; NS-1619 as a Ca(2+)-sensitive K(+) channel activator; and halothane as a TASK-like background K(+) channel activator. The hypoxic response was partially reduced by halothane only, while pinacidil, levcromakalim and NS-1619 had no effect. Interestingly, the effect of doxapram was partially inhibited by NS-1619. Neither pinacidil nor levcromakalim affected the stimulatory effect of doxapram. We conclude that doxapram stimulates the carotid body via a different mechanism than hypoxic chemotransduction.

1 To clarify the effects of doxapram on the baroreflex, we recorded carotid sinus nerve (CSN) activity in isolated and perfused carotid artery bifurcations of rabbits. 2 The CSN activity due to chemoreceptor stimulation was blocked by resection of the nerve branches from the carotid body. After the resection, the CSN activity was correlated to increase of carotid sinus (CS) pressure. 3 Administration of doxapram reduced the CSN activity originating from baroreceptors. The effect of doxapram on baroreceptors was dose dependent and reversible. 4 It is unlikely that doxapram altered CS wall mechanics because CS pressure did not change in the presence of the drug. 5 We conclude that doxapram acts on the cardiovascular system in part by inhibiting the negative feedback loop that originates in CS baroreceptors.