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Plasma chlortetracycline (CTC) concentration data were subjected to Monte Carlo simulation of area under the concentration curve (AUC) values related to bovine respiratory disease pathogen MIC distributions to evaluate target attainment rates. Crossbred Hereford heifers were randomly assigned into two treatment groups. Treatment group (A) received chlortetracycline (CTC) at a target dose of 22 mg/kg of bodyweight daily for 5 consecutive days (n = 8) and group (B) received CTC at 350 mg/head per day (1.5 ± 0.2 mg/kg based on actual bodyweights) for seven consecutive days (n = 8). Non-compartmental analysis was used to calculate plasma-free drug CTC area under the concentration curves. The mean observed (±SD) free drug AUC values were 4.18 (±1.72) μg × h/mL and 0.30 (±0.06) μg × h/mL for treatment groups A and B, respectively. The probability of target attainment for AUC 24 /MIC values of 25 and 12.5 was modeled using Monte Carlo simulations. Treatment group A achieved >90% target attainment (AUC 24 /MIC of 25) at an MIC of 0.06 μg/mL, whereas treatment group B displayed only 12.6% target attainment (AUC 24 /MIC of 12.5) at the lowest MIC evaluated (0.015 μg/mL). Both in-feed CTC regimens failed to obtain a reasonable target attainment rate in light of expected MIC distributions of potential pathogens., (© 2024 John Wiley & Sons Ltd.)

The aim of this work is to improve the solubility and bioavailability of chlortetracycline and the function of the immune response. Chlortetracycline bisulfate and chlortetracycline mesylate were successfully synthesized and characterized with several techniques, including spectroscopy, chromatography and mass spectrometry, which demonstrated that the C4-dimethylamino group of chlortetracycline can accept a proton from sulfuric acid and methanesulfonic acid to form the corresponding salts. In addition, chlortetracycline bisulfate and chlortetracycline mesylate were more soluble in water than chlortetracycline hydrochloride, but the antibacterial activity was not enhanced. The influences of chlortetracycline hydrochloride, chlortetracycline bisulfate and chlortetracycline mesylate on chlortetracycline and immunoglobulin concentrations in mouse serum were also investigated. These results suggested that the chlortetracycline bisulfate and chlortetracycline mesylate have good bioavailability and strong immune response and have potential applications in animal breeding and formulation technologies.

Tetracyclines continue to be important antimicrobials in veterinary medicine. However, the pharmacokinetics (PK) of tigecycline (TIG) and minocycline (MIN) in broiler chickens has not been investigated to date, and the PK of chlortetracycline (CTC) and tetracycline (TET) remains insufficiently researched, especially in terms of absorption. These antimicrobials have never been compared in a single setting in a single species; therefore, the aim of the present study was to compare the PK of TIG, MIN, CTC, and TET in broiler chickens. Each drug (10 mg/kg) was administered intravenously (IV) and orally (PO). The plasma concentrations of each drug were determined by liquid chromatography-tandem mass spectrometry, and the results were analyzed using compartmental and non-compartmental PK models. Despite the fact that all of the studied antimicrobials were administered at an identical IV dose, the area under the concentration-time curve between zero and the last sampling point (AUC 0→t ) for MIN (35,014 ± 3,274 μg × hour/mL) and CTC (41,851 ± 10,965 μg × hour/mL) differed significantly from that determined for TIG (18,866 ± 4,326 μg × hour/mL) and TET (17,817 ± 4,469 μg × hour/mL). After IV administration, the values of AUC 0→t were also directly related to total body clearance values which were significantly higher for TIG (0.56 ± 0.14 L/hour × kg) and TET (0.60 ± 0.14 L/hour × kg) than for CTC (0.25 ± 0.05 L/hour × kg) and MIN (0.29 ± 0.03 L/hour × kg). In turn, after PO administration, TIG was absorbed in only 1.55% ± 0.82, and CTC in 30.54% ± 6.99, whereas the bioavailability of MIN and TET was relatively high at 52.33% ± 3.92 and 56.45% ± 9.71, respectively. The differences in PK parameters between these drugs, despite their structural similarities, suggest that active transport mechanisms may play a role in their absorption and distribution., (Copyright © 2020. Published by Elsevier Inc.)

As veterinary antibiotics (VAs) cause adverse effects on nature, anaerobic digestion (AD) of livestock manure has been receiving attention as an exposure route of VAs. This research evaluated the anaerobic degradation and phase distribution of chlortetracycline (CTC) with its epimer (4-epi-CTC, ECTC) and isomer (Iso-CTC, ICTC). In addition, whether CTC can inhibit not only AD of a substrate but also the degradation of CTC was assessed. Anaerobic batch assays were performed with cattle manure for 30 days by varying the initial concentration of CTC; 0, 10, 25, 50, and 100 mg/L. Approximately 25-43 % (w/w) of CTC was primarily degraded while 18-25 % and 20-26 % of CTC was transformed into ECTC and ICTC, respectively. Up to 88 % (w/w) of the remaining CTC, ECTC, and ICTC was present in the solid phase. In addition, CTC inhibited not only the mineralization of the cattle manure but also the degradation of CTC due to co-metabolism. In conclusion, significant quantities of CTC, ECTC, and ICTC can be exposed to nature by solid phase of anaerobic digestate. The inhibition on AD can reduce the degradation of CTC, ECTC, and ICTC during the AD., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Tetracyclines belong to antimicrobial classes with the highest consumption in veterinary medicine and agriculture, which leads to the contamination of the environment and food products, as well as to antibiotic resistance and adverse drug reactions. Chloro-derivatives of tetracyclines are thought to be relatively more phototoxic than others and belong to the most frequently cited drugs as photosensitizers. Melanins are heterogenous biopolymers determining skin, hair and eye colour. They are biosynthesized in a multistep process in melanocytes. Melanins, besides photoprotective and antioxidant properties, may also contribute to adverse skin drug reactions, which involve e.g. hyperpigmentation disorders and phototoxic reactions. Furthermore, they have the ability to form a drug-melanin complex, which leads to deposition of the drug or its metabolites in pigmented tissues. The aim of the study was to examine the ability of chlortetracycline to form a complex with melanin, as well as the effect of the drug on viability, antioxidant defence system and melanogenesis in normal human epidermal melanocytes exposed to the UVA radiation. The obtained results show for the first time that chlortetracycline forms a complex with melanin polymers, which creates a possibility of the drug accumulation in pigmented tissues. A simultaneous exposition of normal melanocytes to chlortetracycline and to the UVA radiation decreases cell viability, proportionally to the drug concentration and the irradiation time. The phototoxic effect appears to be related to the induction of oxidative stress in melanocytes, mainly through an increase of SOD and a decrease of the CAT activity. Chlortetracycline itself does not influence the melanin content or the activity of tyrosinase. The UVA radiation appeared to be a conditioning factor stimulating melanogenesis, whereas the presence of the drug augmented this effect., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The environmental and human health risk posed by veterinary antibiotics is of global concern. Antibiotic uptake by herbal plants has been studied, but little is known about perennial woody fruit crops. Litchi (Litchi chinensis Sonn.), a longevial fruit tree, is routinely fertilized with animal manure and, therefore, may be at risk of antibiotic uptake into its fruits. This study investigated the degradation of chlortetracycline and doxycycline present in manure used to amend orchard soil, and their subsequent assimilation by litchi plant, as affected by manure application rate. The results show that half-lives of chlortetracycline and doxycycline in soil were decreased by increased manure rate, with an average of 27 and 59 days, respectively. Chlortetracycline was readily transported to litchi shoots and increased with the growth of litchi plants. Doxycycline predominantly remained in the roots, and underwent growth dilution in the plants. The two tetracyclines could not be detected in fruits from litchi trees when applied with manures, at various rates, over 2 years. For litchi, chlortetracycline may pose human health risk through manure application, but doxycycline is unlikely to do so. Long-term field experiments are required to monitor antibiotic accumulation in fruits of perennial fruit trees fertilized with animal manure.

Background: Sensitivity analysis is an essential step in mathematical modeling because it identifies parameters with a strong influence on model output, due to natural variation or uncertainty in the parameter values. Recently behavior pattern sensitivity analysis has been suggested as a method for sensitivity analyses on models with more than one mode of output behavior. The model output is classified by behavior mode and several behavior pattern measures, defined by the researcher, are calculated for each behavior mode. Significant associations between model inputs and outputs are identified by building linear regression models with the model parameters as independent variables and the behavior pattern measures as the dependent variables. We applied the behavior pattern sensitivity analysis to a mathematical model of tetracycline-resistant enteric bacteria in beef cattle administered chlortetracycline orally. The model included 29 parameters related to bacterial population dynamics, chlortetracycline pharmacokinetics and pharmacodynamics. The prevalence of enteric resistance during and after chlortetracycline administration was the model output. Cox proportional hazard models were used when linear regression assumptions were not met., Results: We have expanded the behavior pattern sensitivity analysis procedure by incorporating model selection techniques to produce parsimonious linear regression models that efficiently prioritize input parameters. We also demonstrate how to address common violations of linear regression model assumptions. Finally, we explore the semi-parametric Cox proportional hazards model as an alternative to linear regression for situations with censored data. In the example mathematical model, the resistant bacteria exhibited three behaviors during the simulation period: (1) increasing, (2) decreasing, and (3) increasing during antimicrobial therapy and decreasing after therapy ceases. The behavior pattern sensitivity analysis identified bacterial population parameters as high importance in determining the trajectory of the resistant bacteria population., Conclusions: Interventions aimed at the enteric bacterial population ecology, such as diet changes, may be effective at reducing the prevalence of tetracycline-resistant enteric bacteria in beef cattle. Behavior pattern sensitivity analysis is a useful and flexible tool for conducting a sensitivity analysis on models with varied output behavior, enabling prioritization of input parameters via regression model selection techniques. Cox proportional hazard models are an alternative to linear regression when behavior pattern measures are censored or linear regression assumptions cannot be met.

The purpose of this study was to determine if concentrations of chlortetracycline could be detected in fetal plasma or tissues after administering an oral dose of chlortetracycline (CTC; 500 mg/head/day) reported to be effective in controlling Campylobacter spp. abortions. Five pregnant ewes were administered 250 mg/head twice a day (total dose 500 mg/hd/d) for 7 days. On the beginning of day 7, intravenous catheters were surgically implanted or inserted into the fetus and dam. Plasma samples were collected from the ewe and fetus at various time points before and up to 36 hr after the last dose of CTC. All ewes were then sacrificed, and tissues were harvested from the fetus for drug analysis. Concentrations of CTC in maternal plasma were consistent with our previous study and below the minimum inhibitory concentration of Campylobacter abortion isolates. Concentrations of CTC were below the limit of detection in three of five fetal plasma samples and all of the placenta, amniotic fluid, and fetal stomach contents. Low concentrations were detectable in fetal kidney and liver, suggesting that CTC reaches the fetus, although at a variable and low ratio when compared to maternal concentrations., (© 2017 John Wiley & Sons Ltd.)

The objective of this study was to determine the fate of commonly used veterinary antibiotics in their naturally excreted form when manure-based amendments are applied to soil. Beef cattle were administered sulfamethazine, tylosin, and chlortetracycline and dairy cows were treated with pirlimycin. The resulting manure was composted for 42 d under static or turned conditions and applied at agronomic N rates to sandy, silt, and silty clay loam soils and compared with amendment with corresponding raw manures in sacrificial microcosms over a 120-day period. Antibiotic dissipation in the raw manure-amended soils followed bi-phasic first order kinetics. The first phase half-lives for sulfamethazine, tylosin, chlortetracycline, and pirlimycin ranged from 6.0 to 18, 2.7 to 3.7, 23 to 25, and 5.5-8.2 d, respectively. During the second phase, dissipation of sulfamethazine was negligible, while the half-lives for tylosin, chlortetracycline, and pirlimycin ranged from 41 to 44, 75 to 144, and 87-142 d, respectively. By contrast, antibiotic dissipation in the compost-amended soils followed single-phase first order kinetics with negligible dissipation of sulfamethazine and half-lives of tylosin and chlortetracycline ranging from 15 to 16 and 49-104 d, respectively. Pirlimycin was below the detection limit in the compost-amended soils. After incubating 120 d, antibiotics in compost-amended soils (up to 3.1 μg kg -1 ) were significantly lower than in manure-amended soils (up to 19 μg kg -1 , p < .0001), with no major effect of soil type on the dissipation. Risk assessment suggested that composting can reduce antibiotic resistance selection potential in manure-amended soils., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Fifteen parturient camels given chlortetracycline (CTC) as intrauterine pessaries (3 g/head) were divided into the control group (n = 5), which remained untreated, oxytocin-treated group (50 IU, intramuscular; n = 5), and cloprostenol-treated group (Estrumate, 500 μg, intramuscular; n = 5). Serum samples were collected at 0, 1, 2, 4, 8, 24, 48, and 72 hours after treatment and CTC was determined. The CTC appeared in blood within 1 hour. The maximum concentration of CTC was detected in blood after 72 (543.58 ± 117.85 μg/L), 8 (520.48 ± 13.65 μg/L), and 1 hour (831.98 ± 111.01 μg/L) of administration in control, oxytocin-, and PGF2α-treated camels, respectively. There was a high significant effect of time (P < 0.001) and treatment-by-time interaction (P < 0.001) on serum CTC concentration. In the control group, there was a significant (P < 0.05) increase in CTC concentrations at 72 hours compared to the other times. In the oxytocin group, there was a significant (P < 0.05) decrease in CTC concentrations at 24, 48, and 72 hours compared to its level after 1 or 8 hours. In PGF2α, there was a significant (P < 0.001) decrease in CTC concentrations at 2, 4, 8, 24, 48, and 72 hours compared to its level after 1 hour. Treatment contrast at different time points showed a significant (P < 0.001) increase in CTC concentration after 1 hour in the PGF2α-treated group compared to oxytocin and control groups. By 72 hours, CTC concentrations were significantly (P < 0.05) lower in PGF2α and oxytocin groups than in the control group. In conclusion, serum CTC concentration in dromedary camels increases within 1 hour after intrauterine administration and remains elevated for at least 72 hours in control, oxytocin-, and PGF2α-treated animals., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The objectives of this study were to determine plasma concentrations and pharmacokinetic parameters of feed-grade chlortetracycline (CTC) in sheep after oral administration of 80 or 500 mg/head daily, divided into two equal doses given at 12-h intervals for 8 days. These are the approved, and commonly used but unapproved, feed additive doses, respectively, in the United States for the prevention of ovine infectious abortion. Blood samples were collected just prior to dosing at 0, 12, 24, 72, 96, and 192 h, as well as 4, 8, 12, 24, and 36 h after the last dose, and noncompartmental pharmacokinetic analysis was performed to estimate elimination half-life and area under the plasma concentration-time curve (AUC). Mean observed maximum CTC concentrations (Cmax ) were 20.0 ng/mL (80 mg dose) and 101 ng/mL (500 mg dose). Mean apparent elimination half-life was 18 h (80 mg dose) and 20 h (500 mg dose). Although published data do not exist to estimate plasma CTC concentrations necessary for the prevention of ovine infectious abortion, concentrations reached in our study suggest that either the FDA-approved and FDA-unapproved dosages are not high enough or that the pharmacodynamic parameter relating preventive dose to pathogen minimum inhibitory concentrations is yet to be determined., (© 2014 John Wiley & Sons Ltd.)

Antimicrobial use in food animals may increase antimicrobial resistance in their enteric bacteria that can be transferred to human microbiome. Over 70% of U.S. beef feedlots use non-ionophore in-feed antimicrobials for animal disease control, treatment, or growth promotion. The fraction of feedlots feeding chlortetracycline (CTC), mostly for disease control but also for treatment, has increased since the mid-1990s to present. Quantitative information on the antimicrobial selective pressure on the enteric bacteria of cattle fed CTC is lacking. Hence, the purpose of this study was to develop a deterministic mathematical model of the pharmacokinetics of ingested CTC in a beef steer and estimate the concentration of antimicrobially active (undegraded) CTC in the animal's large intestine. To evaluate the fit of the model to existing data, we also estimated the CTC concentrations in the central circulation, and fresh and aging manure from the steer. The model accounted for CTC abiotic degradation while in the gastrointestinal tract, absorption into the central circulation and tissues, biliary and renal excretion, and removal from the intestine by defecation. The model included an increase in the large intestine volume as the steer grew. We estimated that during CTC feeding to a 300-kg steer for growth promotion, the maximal drug concentration in the large intestine was 0.3 μg/mL; during disease control it was 1.7 μg/mL; and during treatment it was 31.5 μg/mL. The estimated CTC concentrations in the central circulation and the steer's manure agreed reasonably well with published data.

The aim of this study was to investigate whether T-2 toxin, a potent Fusarium mycotoxin, affects the oral absorption of the antibiotic chlortetracycline in pigs. Animals were allocated to blank feed without T-2 toxin (controls), feed containing 111 μg T-2/kg feed, T-2-contaminated feed supplemented with a yeast-derived feed additive, or blank feed supplemented solely with the feed additive, respectively. After 21 days, an intragastric bolus of chlortetracycline was given to assess potential alterations in the pharmacokinetics of this commonly used antibiotic. A significantly higher area under the plasma concentration-time curve and maximal plasma concentration of chlortetracycline was observed after intake of T-2-contaminated feed compared with control. Thus, exposure to T-2-contaminated feed can influence the oral bioavailability of chlortetracycline. This effect could have consequences for the withdrawal time of the drug and the occurrence of undesirable residues in edible tissues., (© 2013 John Wiley & Sons Ltd.)

Chickens were used to investigate plasma disposition of chlortetracycline after single IV (15 mg/kg) and multiple oral administration (60 mg/kg, 5 days) and residue depletion of chlortetracycline after multiple oral doses (60 mg/kg, 5 days). Plasma and tissue samples were analyzed by HPLC. Mean elimination half-lives in plasma were 7.96 and 13.15 h after IV and multiple oral administration. Maximum plasma concentration was 4.33 μg/ml and the interval from oral administration until maximal concentration was 1.79 h. Oral bioavailability was 17.76%. After multiple oral dose, mean kidney, liver and muscle tissue concentrations of chlortetracycline+4-epi-chlortetracycline of 835.3, 192.7, and 126.3 μg/kg, respectively, were measured 1 day after administration of the final dose of chlortetracycline. Chlortetracycline residues were detected in kidney and liver (205.4 and 81.7 μg/kg, respectively), but not in muscle, 3 days after the end of chlortetracycline treatment. The mean chlortetracycline+4-epi-chlortetracycline concentrations were below LOQ at 3 and 5 days after cessation of medication in muscle and liver, respectively. A withdrawal time of 3 days was necessary to ensure that the chlortetracycline residues were less than the maximal residue limits (MRLs) established by the European Union (100, 300, and 600 μg/kg in muscle, liver, and kidney, respectively)., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The effect of various capacitation inducers, i.e. heparin, superoxide anion, bicarbonate, adenosine, and caffeine, and their role in intracellular mechanisms involved in capacitation, were studied in cryopreserved bovine sperm. Capacitation was determined by epifluorescence chlortetracycline, protein tyrosine phosphorylation, and the ability of capacitated sperm to undergo an acrosome reaction and fertilize in vitro matured oocytes. Participation of membrane adenylate cyclase and protein kinases (protein kinase A, protein kinase C, and protein tyrosine kinase) was evaluated indirectly (with specific inhibitors). Involvement of reactive oxygen species (ROS) was determined with scavengers of superoxide anion, hydrogen peroxide, or nitric oxide. Percentages of capacitated (27-29%) and acrosome-reacted sperm (23-26%) did not differ (P > 0.05) among various capacitation inducers. Significantly higher rates of IVF were obtained with heparin (43%) or bicarbonate plus caffeine (45%), when compared with control samples (17%). Adding the membrane adenylate cyclase inhibitor diminished capacitation rates with heparin (8%) or adenosine (10%). There was differential protein kinase participation in response to inducers; protein kinase inhibitors diminished cleavage rates in heparin-capacitated sperm relative to controls. There were differences between and within the studied inducers in protein tyrosine phosphorylation patterns. We inferred that capacitation in cryopreserved bovine sperm was promoted through diverse pathways. Mechanisms triggered by heparin, or caffeine plus bicarbonate-induced capacitation, involved activation of intracellular pathways to optimize fertilizing capability of cryopreserved bovine sperm., ((c) 2010 Elsevier Inc. All rights reserved.)

Chlortetracycline HCl (CTC) has impacted profitable livestock production since 1945. However, pharmacokinetic parameters for CTC in ruminating cattle are unavailable in peer-reviewed literature. A total of 18 steers were randomized to 4.4, 11, or 22 mg/kg/day p.o. CTC treatment groups (n = 6). Chlortetracycline treatment was offered as one-half of the daily dose b.i.d. (160 total doses/group) for 80 days. Blood samples were collected at selected time points throughout an 83-day study and analyzed with a solid phase extraction technique and novel ultrahigh performance liquid chromatography-mass spectroscopy/mass spectroscopy analytical method. Noncompartmental analysis (NCA) determined individual pharmacokinetic parameters by treatment group with coefficient of variation (CV %) estimates. A one-compartment open model with first order absorption and elimination, where absorption rate constant was equal to elimination rate constant, was fitted using nonlinear mixed effects modeling (NLMEM). NLMEM determined the primary pharmacokinetic parameters: volume of distribution (V/F, 40.9 L/kg) and rate constant (k, 0.0478 h(-1)), and the secondary parameters: dose-normalized area under the curve (AUC/D, 0.29 h x microg/L), clearance (Cl/F, 1.8 L/kg/h), elimination half-life (t(1/2), 16.2 h), C(max/Dose) (4.5 ng/mL), and time of C(max) (T(max), 23.3 h) with improved CV estimates over NCA. Dose linearity was confirmed by anova of parameters derived from NCA by treatment group. Further studies are necessary for determining absolute bioavailability and pharmacokinetic-pharmacodynamic relationships of CTC in group fed, ruminating cattle.

Antibiotics are commonly added to animal feed as supplements to promote growth of food animals. However, absorption of antibiotics in the animal gut is not complete and as a result substantial amounts of antibiotics are excreted in urine and feces that end up in manure. Manure is used worldwide not only as a source of plant nutrients but also as a source of organic matter to improve soil quality especially in organic and sustainable agriculture. Greenhouse studies were conducted to determine whether or not plants grown in manure-applied soil absorb antibiotics present in manure. The test crops were corn (Zea mays L.), green onion (Allium cepa L.), and cabbage (Brassica oleracea L. Capitata group). All three crops absorbed chlortetracycline but not tylosin. The concentrations of chlortetracycline in plant tissues were small (2-17 ng g(-1) fresh weight), but these concentrations increased with increasing amount of antibiotics present in the manure. This study points out the potential human health risks associated with consumption of fresh vegetables grown in soil amended with antibiotic laden manures. The risks may be higher for people who are allergic to antibiotics and there is also the possibility of enhanced antimicrobial resistance as a result of human consumption of these vegetables.

Phosphodiesterases (PDEs) are enzymes that degrade cyclic nucleotides. The calcium-calmodulin dependent PDE type 1 (PDE 1) and the cyclic adenosine monophosphate (cAMP)-specific PDE type 4 (PDE 4) have been implicated in sperm function. We tested the hypothesis that specific PDEs regulate capacitation of bovine sperm in a manner independent of those that mediate motility. Our objectives were to determine the effects of inhibiting PDE 1 and PDE 4 on capacitation and motility, and to compare these effects to those of heparin, which is necessary for capacitation of bull sperm in vitro. Fresh sperm were supplemented either with 15 microg/mL heparin (positive control) or the PDE inhibitors vinpocetine (specific for PDE 1) and rolipram (specific for PDE 4), and then incubated for 5 hours. At 0, 3, and 5 hours, samples were assayed for capacitation and motility parameters according to the chlortetracycline (CTC) fluorescent pattern B and computer-assisted sperm analysis, respectively. A higher percentage of CTC pattern B sperm relative to heparin controls was observed at 0 and 3 hours when sperm were incubated with vinpocetine. After 5 hours, the percentage of heparin- and vinpocetine-treated sperm showing pattern B did not differ (P >.05). Rolipram did not affect CTC patterns (P >.05; n = 4). Vinpocetine and heparin both reduced the percentage of progressively motile sperm after 3 and 5 hours, but vinpocetine reduced it more than heparin (P <.05; n = 4). Rolipram transiently increased linearity versus sperm with heparin (P <.05; n = 4). To further test the hypothesis that PDE 1 inhibition permits capacitation, we conducted in vitro fertilization. Vinpocetine did not support the ability of sperm to penetrate homologous oocytes (n = 5). Although cAMP regulation by PDE 1 may occur early during capacitation, downstream events appear to prevent full capacitation from occurring prematurely.

Bacterial whole-cell biosensors were used to measure the concentration of chlortetracycline (CTC) in the feces of pigs. In this study, the Escherichia coli biosensor used has a detection limit of 0.03 mg/kg CTC in pig feces. The tetracycline concentration was correlated with the appearance and maintenance of fecal coliform bacteria resistant to tetracycline. Initially, large quantities of water-extractable CTC were excreted from the pigs and measurable amounts were detected even at 30 days after treatment cessation. This led to a sharp rise in the number of tetracycline resistant coliform bacteria in the feces, to within the same order of magnitude as the total coliform count. The high level of tetracycline resistance was maintained in spite of the declining concentration of tetracycline.

Chlortetracycline (CTC) is a broad spectrum antibiotic, licensed for use without any withdrawal period, in chickens laying eggs intended for human consumption. In the European Union, a maximum residue limit (MRL) in eggs of 200 microgram/kg for the sum of the concentrations of CTC and its 4-epimer (4-epi-CTC) has been established. Two major CTC metabolites have been identified in eggs. These compounds, iso-CTC and 4-epi-iso-CTC, have never previously been shown to be significant products of CTC metabolism in poultry or in any other species. The total amount of CTC present in eggs, as all of the chemical forms measured, can exceed the MRL by anything up to a factor of four (170-820 micrograms/kg).

The disposition of oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) was measured after intravenous and oral administration to pigs. Eighteen healthy pigs (six for each compound) weighing 22-43 kg received a dose of 10 mg/kg intravenously, and 45 mg/kg (OTC and TC) or 40 mg/kg (CTC) orally in both a fasted and a fed condition in a three-way crossover design. The three tetracyclines were present in plasma up to 30 hours after intravenous and after oral administration to fasted as well as fed pigs. The volume of distribution was 1.4, 1.2 and 0.7 L/kg body weight for OTC, TC and CTC respectively. The bioavailability was in general low for all the three tetracyclines. The presence of food did not affect the bioavailability of OTC, which was only 3% in both fasted and fed pigs. For TC there was a significantly higher bioavailability in fasted (18%) than in fed (5%) pigs, whereas for CTC the difference was not significant, being 11% in fasted vs. 6% in fed pigs. Even though the presence of food affected the bioavailability only for TC, it prolonged the absorption phase for all three tetracyclines. Based on the bioavailability and the resulting plasma concentrations, it is concluded that it is not possible to obtain a therapeutically active concentration in plasma or tissues after oral administration of any of the three tetracyclines to fed or fasted pigs.

Twenty-four hogs were fed a ration for 14 days containing three times the recommended label dose of a combination drug which included sulfamethazine, chlortetracycline and penicillin G. Groups of six hogs were slaughtered 0, 2, 4, or 8 days after withdrawal. Six untreated control hogs were slaughtered 5 days before the first group, of six treated hogs, were slaughtered. Residue concentrations were determined in kidney, liver, muscle, serum and urine. At zero withdrawal the kidney from one hog contained 0.018 mg penicillin G per kg and the serum from the same hog contained 0.016 mg penicillin G per litre. Penicillin G was not detected in any other samples that were analysed. Chlortetracycline concentrations in tissues at zero withdrawal time were below accepted Canadian Maximum Residue Limits (MRL) for chlortetracycline of 1 mg/kg in muscle, 2 mg/kg in liver and 4 mg/kg in kidney and were below the limit of quantitation in all tissues 4 days after withdrawal. Sulfamethazine persisted in the tissues longer than penicillin G or chlortetracycline. Sulfamethazine concentrations were above the Canadian MRL of 0.1 mg/kg at zero withdrawal time and did not decrease to below the MRL until 8 days after withdrawal. Our results suggest that, if the label withdrawal period of 10 days is observed, an increase in the dosage of up to three times the recommended rate is unlikely to increase significantly the risk that residues would occur in the tissues of treated hogs at concentrations which exceed MRLs. Sulfamethazine concentrations in all matrices decreased after storage at -76 degrees C for 6 months.

Violative chlortetracycline (CTC) residues in excess of the maximum residue limit (MRL) have been identified in 0.9% of all pigs tested at slaughter in Northern Ireland. Three experiments were carried out to investigate the possible reasons. In Experiment 1, pigs were fed CTC at therapeutic levels (300 mg kg-1 head-1 d-1) for 7 days and were slaughtered at day 0, 2, 4, 6, 8 and 10 following CTC withdrawal. Muscle, liver and kidney cortex and medulla samples were analysed for CTC residues by using high-performance liquid chromatography (HPLC). In all tissues, residues were less than the MRL from day 2 onwards. Mean CTC concentrations in kidney cortex were greater than medulla concentrations (p < 0.05). In Experiment 2, feed spiked with a sub-therapeutic dose of CTC (40 mg kg-1) was fed to six pigs that were slaughtered after 4, 8 and 12 days of medication. Violative CTC residues were not detected. In Experiment 3, short term supra-therapeutic administration was examined. Eight pigs received 500 mg kg-1 CTC head-1 d-1 for 1 or 2 days and were killed in pairs, 24 and 48 h following the final medicated feed. Violative levels were detected in both groups after 24 h only. It is concluded that: firstly, recommended CTC withdrawal periods are sufficient to avoid violative carcass residues; secondly, violative residues do not arise from sub-therapeutic dosing but can arise from supra-therapeutic dosing which could occur with inadequately mixed feed; and thirdly, the difference in kidney cortex and medullary CTC concentrations is significant from a regulatory perspective.

In a study involving 18 piglets divided into three groups (A, B and C), the effects of dietary calcium and citric acid, and feeding technique on chlortetracycline bioavailability were examined. Groups of 6 animals received a basal diet with either 0.7% (group A) or 1.4% calcium (groups B and C). Citric acid was not included in diets of the first experimental period. In the second period, either 1.5% (groups A and B) or 3.0% (group C) citric acid was added to the diet. In both experimental periods, chlortetracycline was administered once intravenously (7.5 mg/kg b.w.) and once orally (30 mg/kg b.w.). After each administration, blood samples were taken at regular intervals in order to determine chlortetracycline serum concentrations by a microbiological method. Following oral chlortetracycline intake, low dietary calcium or citric acid addition to the diet produced increased chlortetracycline serum concentrations. Chlortetracycline bioavailability was 12.6% at 0.7% dietary calcium, and 9.5% at 1.4% dietary calcium. Enteral chlortetracycline absorption was improved 65% with 1.5% or 3.0% dietary citric acid supplementation. An 8-hour delay of feed intake following oral chlortetracycline intake did not significantly influence chlortetracycline bioavailability.

We describe the absorption of chlortetracycline from the emptied hydrocele sac, which was instilled to treat a primary hydrocele of the testis. The study included 7 patients and 2 control subjects who were given 500 mg. chlortetracycline. Plasma concentration was determined at 0, 1/2, 1, 2, 4, 6, 12 and 24 hours after instillation, and in 2 patients plasma levels also were determined at 48 and 72 hours. The area under the plasma concentration-time curve (AUC1) was calculated in each case by using the trapezoidal rule. In the control group the plasma level was determined at 0, 1, 2, 4 and 6 hours after instillation. The area under the plasma concentration-time curve (AUC2) was calculated by the formula AUC2 = Co/Kc. The fraction F of absorption can be expressed as F = AUC1/AUC2; median F = 0.67 (range 0.41 to 0.92). We conclude that chlortetracycline passes readily and almost completely through the tunica vaginalis lining the hydrocele sac.

40 adult White Californian rabbits were monitored for serum levels, soft tissue concentrations, and biological half-life of technical chlorotetracycline (Aureovit 12 C40 -- SPOFA), chlorotetracycline chloride (Farmitalia substance), tetracycline chloride (tetramyocine tablets for veterinary use -- SPOFA), and oxytetracycline chloride (oxymycoine in powder form for solution for veterinary use -- SPOFA), following application of 20 micrograms.kg-1. All tetracyclines tested were orally administered by gavage, following dissolution or suspension (Aureovit 12 C40). Statistically significant differences were found to exist among serum levels of various tetracyclines, with the 1st to 11th hours from administration, whereafter differences turned minimal between the 11th and 24th hours. Differences were found to exist also among concentrations in various organs.

Chlortetracycline hydrochloride was administered intra-arterially (11 mg/kg) and as an oral drench (33 mg/kg) to ten 21.0-31.5-kg pigs. Five of the pigs were fasted 18 h prior to dosing and five of the pigs were fed ad libitum prior to dosing. The mean volume of distribution determined by area-under-the-curve calculations for the fasted pigs (0.967 +/- 0.210 l/kg) was significantly less (P less than 0.05) than the mean volume of distribution for the fed pigs (1.39 +/- 0.31 l/kg). Mean total body clearance of the drug was also significantly less (P less than 0.05) in the fasted pigs (0.165 +/- 0.055 l/kg/h) as compared to the fed pigs (0.307 +/- 0.053 l/kg/h). The elimination constants (beta) were not found to be statistically different (P less than 0.05): 0.1811 +/- 0.0057 for the fasted pigs; 0.2260 +/- 0.0461 for the fed pigs. The bioavailability for both groups was similar; 19.12 +/- 8.3% for the fasted pigs and 17.88 +/- 5.3% for the fed pigs. In a second experiment three groups of six pigs which weighed 34.5-44.1 kg were fed a corn-soy diet ad libitum. The rations were fortified with chlortetracycline at 100, 400 or 1000 mg chlortetracycline hydrochloride/kg feed. Chlortetracycline concentrations were determined in plasma samples collected over a 6-day period. Plasma chlortetracycline concentrations reach a plateau within 24 h after initial access to the trial diets and were highly correlated with the dose of the drug consumed (r2 = 0.97).

The influence of different modes of feeding on the bioavailability of orally administered chlortetracycline was studied in weaned pigs. The animals were divided into three groups receiving a dry, a moist or a soup diet, respectively. CTC was applied at a concentration of 6000 ppm and 2500 ppm to each diet and the oral dosage of CTC was 40 mg chlortetracycline/kg bodyweight. The results of the experiments show that the pharmacokinetics of orally applied chlortetracycline are significantly influenced by the mode of feeding. A significantly higher bioavailability was observed with soup feeding compared with moist or dry food. To achieve a therapeutic blood level of 0.5-1.5 micrograms chlortetracycline/ml blood, 20-30 mg chlortetracycline/kg bodyweight/12 h and 30-40 mg chlortetracycline/kg bodyweight/12 h should be applied to soup and dry or moist feed, respectively.

18 piglets were fed either a dry, humid or soup diet and each animal was dosed with 40 mg chlortetracycline/kg bodyweight. The chlortetracycline-concentration in the diet was 2500 mg/kg air-dried feed. After a single oral dosage the absorption of chlortetracycline occurred significantly faster from the soup diet, resulting in higher serum levels as well as prolonged elevated serum concentrations of CTC compared with the other two diets. Using a mathematical model, serum concentrations over a 5-day period with repeated dosage of CTC were calculated. Based on this dates we recommend the following dosage regime for chlortetracycline: 20-30 mg CTC/kg bodyweight/12 h for soup feeding and 30-40 mg CTC/kg bodyweight/12 h for dry or humid feeding.

Influence of non-ionic tensides on liberation of chlorotetracycline hydrochloride from ointment bases was investigated. Non-ionic tensides were found to enhance liberation of chlorotetracycline hydrochloride from lipophilic ointment bases, while liberation of this antibiotic from hydrophilic ointment bases proved to be depressed.

The pharmacokinetics of chlortetracycline (CTC) in plasma and bile after intravenous administration in turkeys was ascertained. After a dose of CTC (0.9 mg/kg) was administered IV, 8.5% of the dose appeared in the bile in 4 hours. The peak bile/plasma concentration ratio for CTC was 254 at 2 hours. The bile/plasma concentration ratio was greater than 1 from 10 to 240 minutes after CTC administration.

Chlorotetracycline fluorescence changes were studied in isolated snail (Helix pomatia) neurons. It was shown that the properties of chlorotetracycline fluorescence satisfy those necessary for Ca-sensitive probes. Chlorotetracycline fluorescence increased during membrane depolarization induced by K+ increase in the medium or by addition of veratridine. Both effects were absent in Ca-free solution or in Cd-containing medium. Caffeine also induced an increase in chlorotetracycline fluorescence. This effect is, probably, a result of Ca release from intracellular stores, because it does not depend on extracellular Ca.

A simple, rapid procedure is described for the simultaneous quantification of 3 tetracycline drugs in bovine milk. Samples are prepared by dilution with an EDTA/phosphate buffer solution and filtration through a molecular weight cutoff filter. Analytes are concentrated on-column using a reverse-phase gradient elution system of oxalic acid, acetonitrile, and methanol. The limits of quantitation are approximately 15-50 ng/mL and the limits of detection are 10-20 ng/mL, depending on the compound. For oxytetracycline, over the range 50-1200 ng/mL, the average recovery and intralaboratory coefficient of variation were 97% and 4.1%, respectively. Over the same range, these parameters were, respectively, 97% and 5.0% for tetracycline, and 89% and 6.4% for chlortetracycline. The applicability of this procedure is demonstrated by separation and detection of incurred tetracycline residues in milk from treated animals.

After dosing laying hens orally with tetracycline (TC) through either drinking water (0.25 and 0.5 g/l for 5 days) or feed (300 and 600 ppm for 7 days), and chlortetracycline (CTC) through feed (600 ppm) residues were determined by an agar plate diffusion technique in cylinders with Bacillus cereus as test-organism, separately for albumen and for yolk. The sensitivity threshold was 0.07 micrograms/g in albumen and 0.15 micrograms/g in yolk for TC and 0.01 micrograms/g in albumen and 0.06 micrograms/g in yolk for CTC. Drug excretion via egg was 3-fold higher for TC than for CTC. The drug was excreted preferentially into the yolk (about 75% of the total amount) and the elimination period lasted between 6 and 11 days for TC and 9 days for CTC, after treatment. Tetracycline use in laying hens is discussed, taking into consideration the proposals presented by the joint FAO/WHO Expert Committee on Food Additives.