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What Is Already Known About This Subject: • The cholinergic system is important for different central nervous system functions, including memory, learning and attention. Scopolamine, a centrally active muscarinic antagonist, has been used to model dementia and to demonstrate the pharmacological effects of cholinergic drugs, but for most effects the concentration-effect relationships are unknown., What This Study Adds: • We determined the pharmacokinetic-pharmacodynamic relationships of scopolamine using a multidimensional central nervous system test battery in a large group of healthy volunteers. The results suggested there are various functional cholinergic systems with different pharmacological characteristics, which can be used to study the effects of drugs that directly or indirectly modify cholinergic systems. The design of such studies should take the different concentration-effect relationships into account. AIM(S) Although scopolamine is a frequently used memory impairment model, the relationships between exposure and corresponding central nervous system (CNS) effects are mostly unknown. The aim of our study was to characterize these using pharmacokinetic-pharmacodynamic (PK-PD) modelling., Methods: In two double-blind, placebo-controlled, four-way crossover studies, 0.5-mg scopolamine was administered i.v. to 90 healthy male subjects. PK and PD/safety measures were monitored pre-dose and up to 8.5 h after administration. PK-PD relationships were modelled using non-linear mixed-effect modelling., Results: Most PD responses following scopolamine administration in 85 subjects differed significantly from placebo. As PD measures lagged behind the plasma PK profile, PK-PD relationships were modelled using an effect compartment and arbitrarily categorized according to their equilibration half-lives (t(1/2) k(eo) ; hysteresis measure). t(1/2) k(eo) for heart rate was 17 min, saccadic eye movements and adaptive tracking 1-1.5 h, body sway, smooth pursuit, visual analogue scales alertness and psychedelic 2.5-3.5 h, pupil size, finger tapping and visual analogue scales feeling high more than 8 h., Conclusions: Scopolamine affected different CNS functions in a concentration-dependent manner, which based on their distinct PK-PD characteristics seemed to reflect multiple distinct functional pathways of the cholinergic system. All PD effects showed considerable albeit variable delays compared with plasma concentrations. The t(1/2) k(eo) of the central effects was longer than of the peripheral effects on heart rate, which at least partly reflects the long CNS retention of scopolamine, but possibly also the triggering of independent secondary mechanisms. PK-PD analysis can optimize scopolamine administration regimens for future research and give insight into the physiology and pharmacology of human cholinergic systems., (© 2011 Centre for Human Drug Research. British Journal of Clinical Pharmacology © 2011 The British Pharmacological Society.)

Aim: In determining the acute effects of alcohol, it is helpful if alcohol concentrations are maintained at stable levels, to facilitate the interpretation of the results. Recently, an alcohol clamping method was developed that resulted in stable alcohol concentrations for hours. The aim of this study was to test a range of central nervous system (CNS) effects under pseudo-steady-state conditions., Methods: To achieve a pseudo-steady state of 0.6 g l(-1), breath alcohol concentrations (BrAC) were frequently measured and fed back into a spreadsheet-based program to guide intravenous dosing. CNS effects were frequently measured throughout the clamp., Results: The clamping paradigm resulted in a pseudo-steady-state BrAC of 0.61 g l(-1) (coefficient of variation 6.2%). A plateau was maintained from 25 to 300 min and caused significant effects on smooth pursuit eye movements [-9.7%, 95% confidence interval (CI) -12.4, -7.1], adaptive tracking (-3.4%, 95% CI -4.5, -2.2), visual analogue scale (VAS) alertness (-13 mm, 95% CI -20, -6), VAS alcohol effects (16 mm, 95% CI 7, 25) and body sway (21.3%, 95% CI 1.8, 45). Some effects (like smooth pursuit eye movements) closely followed the relatively stable alcohol concentrations, whereas others (such as body sway and VAS alcohol effects) fluctuated during the plateau phase., Conclusions: Most CNS effects of alcohol showed a trend to change over time, despite stable concentrations. Other variables remained stable under pseudo-steady-state conditions. The intravenous clamping method provides precise control over BrAC levels and allows frequent repetition of different CNS measurements. These features make this technique eminently suitable to study the complex pharmacodynamic effects of acute alcohol administration.

Tedisamil, a class III antiarrhythmic drug, is a P-glycoprotein substrate. Tedisamil treatment may implicate coadministration with class IV antiarrhythmics such as verapamil, a P-glycoprotein inhibitor. Pharmacokinetic and pharmacodynamic interactions between tedisamil and verapamil were evaluated in a double-blind, crossover study. Twelve healthy volunteers received a 3-day treatment of tedisamil (100 mg bid), verapamil (180 mg bid), a combination of these drugs, or placebo. Blood pressure and electrocardiograms were assessed daily and cardiac output and pharmacokinetics on day 3. Combination of tedisamil and verapamil increased tedisamil plasma concentrations (AUC(0-12 h): +77%, CI(90%): +51% to +108%; C(max): +78%, CI(90%): +57% to +102%) compared to tedisamil monotreatment but decreased plasma concentrations of verapamil (AUC(0-12 h): -21%, CI(90%): -32% to -8%; C(max): -28%, CI(90%): -39% to -14%) and norverapamil (AUC(0-12 h): -17%, CI(90%): -28% to -6%; C(max): -20%, CI(90%):-29% to -10%) compared to verapamil monotreatment. Compared to placebo, verapamil and the combination treatment increased PR by 23.5 (CI(95%): 17.9 to 29.2) ms and 12.2 (5.7 to 17.0) ms, respectively. Compared to placebo, tedisamil and the combination treatment increased QTc by 27.8 (15.8 to 39.8) ms and 45.7 (33.7 to 57.7) ms, respectively. Thus, concomitant use of tedisamil with P-glycoprotein inhibitors likely results in clinically significant drug interactions.

Aims: Alcohol effects or drug-alcohol interactions are preferably studied at constant blood levels. To achieve pseudo-steady state levels, various methods are used, which usually produce adequate averages but variable individual concentration profiles. The aim was to compare two modes of alcohol administration: a 'two-step prekinetic procedure' and a 'clamping method'., Methods: The two-step prekinetic procedure started with determination of individual pharmacokinetic (PK) parameters, during a prestudy occasion. Individual infusion regimens were calculated afterwards, based on a pseudo-steady state breath alcohol concentration (BrAC) of 0.65 g l(-1) and applied on a separate occasion. For the clamping procedure, a spreadsheet-based paradigm was developed using BrAC-guided adjustments of infusion rates, to maintain stable BrAC levels of 0.6 g l(-1)., Results: The mean BrAC during clamping [0.61 g l(-1), 95% confidence interval (CI) 0.58, 0.63] did not differ from its intended level of 0.6 g l(-1) (1.0% on average). In contrast, the mean BrAC during the prekinetic procedure was significantly lower than the 0.65 g l(-1) set-point (0.59 g l(-1), 95% CI 0.54, 0.63) and deviated from this target by 9.7% on average. The clamping method also showed less variation between subjects [coefficient of variation (CV) 6.2%] compared with the prekinetic procedure (CV 14.6%)., Conclusions: Although the two methods differ considerably in their approach, clamping of BrAC resulted in more accurate alcohol levels than infusion based on PK modelling and does not require an extra prestudy occasion. The novel alcohol clamping paradigm can be of value in future studies of alcohol interactions or the pharmacodynamics of acute alcohol administration.

Context: Knowledge on the relationship between the autonomic nervous system and subclinical hyperthyroidism is mainly based upon cross-sectional studies in heterogeneous patient populations, and the effect of restoration to euthyroidism in subclinical hyperthyroidism has not been studied., Objective: We investigated the long-term effects of exogenous subclinical hyperthyroidism on the autonomic nervous system and the potential effects of restoration of euthyroidism., Design: This was a prospective single-blinded, placebo-controlled, randomized trial., Setting: The study was performed at a university hospital., Patients: A total of 25 patients who were on more than 10-yr TSH suppressive therapy after thyroidectomy was examined., Intervention: Patients were studied at baseline and subsequently randomized to a 6-month thyroid hormone substitution regimen to obtain either euthyroidism or maintenance of the subclinical hyperthyroid state., Main Outcome Measures: Urinary excretion of catecholamines and heart rate variability were measured. Baseline data of the subclinical hyperthyroidism patients were compared with data obtained in patients with hyperthyroidism and controls., Results: Urinary excretion of norepinephrine and vanillylmandelic acid was higher in the subclinical hyperthyroidism patients compared with controls and lower compared with patients with overt hyperthyroidism. Heart rate variability was lower in patients with hyperthyroidism, intermediate in subclinical hyperthyroidism patients, and highest in the healthy controls. No differences were observed after restoration of euthyroidism., Conclusions: Long-term exogenous subclinical hyperthyroidism has effects on the autonomic nervous system measured by heart rate variability and urinary catecholamine excretion. No differences were observed after restoration to euthyroidism. This may indicate the occurrence of irreversible changes or adaptation during long-term exposure to excess thyroid hormone that is not remedied by 6-month euthyroidism.

Background: Epidemiologic studies suggest that garlic may have beneficial effects on risk factors associated with cardiovascular disease (CVD). However, these findings are not unambiguously supported by randomized placebo-controlled clinical trials., Objective: We sought to investigate the effects of a chemically well-characterized garlic preparation on biomarkers for inflammation, endothelial function, and lipid metabolism in subjects with risk factors for CVD., Design: This was a double-blind, randomized, placebo-controlled trial in 90 overweight [body mass index (in kg/m2) > 24.5] subjects aged 40-75 y who smoked >10 cigarettes/d. The subjects were randomly assigned to 3 parallel treatment groups: garlic powder (2.1 g/d), atorvastatin (40 mg/d), or placebo. Duplicate measurements were performed at baseline and after 1 and 3 mo of treatment. Treatments were compared with analysis of covariance with baseline as the covariate, and differences between the treatments were reported as mean percentage difference and corresponding 97.5% CI., Results: None of the variables showed significant differences between the garlic-treated and the placebo groups. In contrast, compared with the placebo group, atorvastatin treatment resulted in significantly lower plasma concentrations of C-reactive protein (20.2%; 1.7%, 35.3%), total cholesterol (37.2%; 33.1%, 41.1%), LDL cholesterol (52.7%; 47.9%, 57.1%), triacylglycerols (31.9%; 20.8%, 41.5%), and tumor necrosis factor alpha (TNF-alpha; 41.9%; 19.0%, 58.3%) and increased the ratio of ex vivo whole blood lipopolysaccharide-stimulated to nonstimulated TNF-alpha concentrations (109.7%; 37.9%, 218.9%)., Conclusion: We conclude that a chemically well-characterized garlic preparation has no significant effect on inflammatory biomarkers, endothelial function, or lipid profile in normolipidemic subjects with risk factors for CVD.

Background: The angiotensin-converting enzyme (ACE) inhibitors have complicated and poorly characterized pharmacokinetics. There are two binding sites per ACE (high affinity "C", lower affinity "N") that have sub-nanomolar affinities and dissociation rates of hours. Most inhibitors are given orally in a prodrug form that is systemically converted to the active form. This paper describes the first human physiologically based pharmacokinetic (PBPK) model of this drug class., Methods: The model was applied to the experimental data of van Griensven et. al for the pharmacokinetics of ramiprilat and its prodrug ramipril. It describes the time course of the inhibition of the N and C ACE sites in plasma and the different tissues. The model includes: 1) two independent ACE binding sites; 2) non-equilibrium time dependent binding; 3) liver and kidney ramipril intracellular uptake, conversion to ramiprilat and extrusion from the cell; 4) intestinal ramipril absorption. The experimental in vitro ramiprilat/ACE binding kinetics at 4 degrees C and 300 mM NaCl were assumed for most of the PBPK calculations. The model was incorporated into the freely distributed PBPK program PKQuest., Results: The PBPK model provides an accurate description of the individual variation of the plasma ramipril and ramiprilat and the ramiprilat renal clearance following IV ramiprilat and IV and oral ramipril. Summary of model features: Less than 2% of total body ACE is in plasma; 35% of the oral dose is absorbed; 75% of the ramipril metabolism is hepatic and 25% of this is converted to systemic ramiprilat; 100% of renal ramipril metabolism is converted to systemic ramiprilat. The inhibition was long lasting, with 80% of the C site and 33% of the N site inhibited 24 hours following a 2.5 mg oral ramipril dose. The plasma ACE inhibition determined by the standard assay is significantly less than the true in vivo inhibition because of assay dilution., Conclusion: If the in vitro plasma binding kinetics of the ACE inhibitor for the two binding sites are known, a unique PBPK model description of the Griensven et. al. experimental data can be obtained.

Background: Hereditary angioedema (HAE) is a congenital disorder with recurrent attacks of localized swelling of submucosal tissue, subcutaneous tissue, or both caused by a deficiency of the plasma protein C1 inhibitor (C1 esterase inhibitor [C1INH])., Objective: We sought to evaluate the effects of recombinant human C1INH (rhC1INH) isolated from the milk of transgenic rabbits in 12 asymptomatic patients with HAE., Methods: rhC1INH was intravenously administered at doses of 6.25 to 100 U/kg on 2 occasions., Results: rhC1INH appeared safe and was well tolerated. The course of functional C1INH in plasma showed a full initial recovery (dose-normalized maximum concentration of about 0.02 U/mL/U/kg) and a dose-dependent clearance of rhC1INH. After infusion of rhC1INH at 100 U/kg, a clearance of approximately 13 mL/min, a half-life of approximately 3 hours, and a volume of distribution of approximately 3 L were observed. Infusion at this dose led to functional C1INH levels in plasma of at least twice the normal level for about 2 hours and greater than 0.4 U/mL for about 9 hours. rhC1INH displayed dose-dependent biologic activity by increasing the C4 level, which was about 2-fold at 12 hours after rhC1INH at 100 U/kg, and decreasing levels of cleaved C4., Conclusion: The observed safety profile and biologic activity of rhC1INH warrants further clinical studies to assess its efficacy in treating HAE attacks.

Background: Tacrolimus has a narrow therapeutic window, and bioavailability is known to vary considerably between renal transplant recipients. Most centers still rely on measurement of trough levels, but there are conflicting reports on the correlation between tacrolimus trough levels and systemic exposure, as measured by the area-under-the-concentration-over-time curve (AUC((0-12h)))., Methods: We developed and validated a two-compartmental population-based pharmacokinetic model with Bayesian estimation of tacrolimus systemic exposure. Subsequently, we used this model to apply prospectively AUC-guided dosing of tacrolimus in 15 consecutive renal transplant recipients. The main objective was to study intrapatient variability in the course of time., Results: Bayesian forecasting with a two-point sampling strategy, a trough level, and a second sample obtained between two and four hours post-dose significantly improved the squared correlation with the AUC((0-12h)) (r(2)= 0.94). Compared with trough level monitoring only, this approach reduced the 95%-prediction interval by 50%. The Bayesian approach proved to be feasible in clinical practice, and provided accurate information about systemic tacrolimus exposure in individual patients. In the AUC-guided dosing cohort the apparent clearance of tacrolimus decreased gradually over time, which was not reflected in corresponding trough levels., Conclusion: This simple, flexible method provides the opportunity to tailor immunosuppression, and should help minimize tacrolimus-related toxicity, such as nephrotoxicity and post-transplant diabetes mellitus.

Non-adrenergic non-cholinergic (NANC) nerves release bronchoactive tachykinins such as substance P (SP) and neurokinin A (NKA) that can induce features of asthma. The airway response to NKA in humans closely resembles that of methacholine (M). Hence, we investigated the relationship between airway responsiveness to NKA and M in subjects with asthma. To this end, we analyzed baseline data of 27 subjects with mild persistent asthma (20F/7M) 19-46 y; FEV1 81-136% pred.; PC20FEV1 (M)<80 micromol/mL) participating in a proof-of-concept study. All subjects were non-smokers and asthma was controlled by on demand short-acting beta2-agonists only. Dose-response curves to M (0.15-80 micromol/mL) and NKA (3.4 (10(-3))-0.88 micromol/mL) were performed on two separate days, and airway response was measured by FEV1 until a > or = 20% fall from baseline (PC20FEV1). Twenty-two subjects reached a PC20FEV1 on both occasions. The PC20FEV1 values of both agonists correlated significantly (Spearman's r=-0.721; p=0.0002), and the relationship was given by 10log(PC20FEV1(NKA))= -1.36 + (0.60 x 10log(PC20FEV1(M)). We have demonstrated a significant relationship between airway responsiveness to NKA and methacholine in asthma. This suggests that both agonists may share common final pathways in causing bronchoconstriction in patients with mild persistent asthma. Based on our data and previous studies in asthma, it can be hypothesized that this direct NKA-induced bronchoconstrictor response may be mediated by predominant stimulation of the tachykinin NK-2 receptors on airway smooth muscle cells.

Aims: To characterize the pharmacokinetics of fumarates in healthy subjects., Methods: Ten subjects received a single fumarate tablet (containing 120 mg of dimethylfumarate and 95 mg of calcium-monoethylfumarate) in the fasted state and after a standardized breakfast in randomized order. Prior to and at fixed intervals after the dose, blood samples were drawn and the concentrations of monomethylfumarate, the biologically active metabolite, as well as dimethylfumarate and fumaric acid were measured using high-performance liquid chromatography., Results: After a lag time, a transient increase in serum monomethylfumarate concentrations in the blood was observed, whereas dimethylfumarate and fumaric acid concentrations remained below the detection limit. The tlag was 240 min [range 60-603 min; 95% confidence interval (CI) 139, 471] shorter when the tablet was taken after an overnight fast (90 min; range 60-120 min; 95% CI 66, 107) than when taken with breakfast (300 min; range 180-723 min; 95% CI 0, 1002). The tmax was 241 min (range 60-1189 min, 95% CI 53, 781) shorter when the tablet was taken after an overnight fast (182 min; range 120-240 min; 95% CI 146, 211) than when taken with breakfast (361 min; range 240-1429 min; 95% CI 0, 1062). The mean Cmax for monomethylfumarate in the blood of fasting subjects was to 0.84 mg l(-1) (range 0.37-1.29 mg l(-1); 95% CI 0.52, 1.07) and did not differ from that in fed subjects (0.48 mg l(-1); range 0-1.22 mg l(-1); 95% CI 0, 5.55)., Conclusions: The pharmacokinetics of monomethylfumarate in healthy subjects after a single tablet of fumarate are highly variable, particularly after food intake. Further experiments exploring the pharmacokinetics of oral fumarates are warranted in order to elucidate the mechanisms underlying variability in response in patients., (Copyright 2004 Blackwell Publishing Ltd)

Aim: To assess the effects of the motilin receptor antagonist RWJ-68023 on basal and motilin-stimulated proximal gastric volume., Methods: Eighteen healthy male volunteers received RWJ-68023 in two different doses or placebo for 135 min. After 45 min, subjects received a motilin infusion for 90 min. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored using visual analogue scales. Motilin and RWJ-68023 concentrations were assessed by radioimmunoassay and liquid chromatography-mass spectrometry, respectively., Results: Both dosages of RWJ-68023 were safe and well tolerated. The most common adverse events were of gastrointestinal origin. RWJ-68023 did not affect basal proximal gastric volume, but the high-dose RWJ-68023 reduced the contractile effect of motilin on the stomach. This antagonizing effect of RWJ-68023 was only significant (P = 0.014) during the distension procedure., Conclusions: The RWJ-68023 doses used in this study were selected to accomplish plasma concentrations that would block the motilin effect entirely. However, the antagonizing effect of RWJ-68023 was partial and only present when the tonic condition of the stomach was modulated by motilin.

Background: Therapeutic drug monitoring of cyclosporin A (CsA) is an obvious necessity because of its unpredictable absorption and narrow therapeutic window. The use of limited sampling models (LSMs) has improved the estimation of the systemic exposure [area under curve (AUC)] compared with C(0h) monitoring, but these equations are rigid and not reliable in patients with an abnormal absorption profile. We developed and validated a limited sampling (t=0, 2 and 3 h) strategy, based on a compartmental population pharmacokinetic (PK) model for CsA after kidney transplantation alone (KTA) and simultaneous pancreas-kidney transplant (SPKT) recipients, a group of patients with unpredictable absorption kinetics., Methods: A two-compartment model with lag time and first-order absorption was calculated using a PK software package from data of 20 KTA and SPKT recipients and validated prospectively in 20 KTA and 20 SPKT recipients. Calculated population PK parameters were individualized for each of the remaining 40 patients based on their CsA dosing and on one or a combination of measured CsA blood concentrations using the Bayesian fitting method. AUCs were calculated from individualized PK parameters. AUCs were also calculated using previously published LSMs. Relationships between AUCs calculated by the models and the 'golden standard' AUC (trapezoidal rule) were investigated by Pearson correlation test., Results and Conclusions: A population two-compartment model is presented to reliably estimate the CsA AUC in KTA and SPKT recipients. The performance of the model to estimate the AUC is comparable to the performance of two published LSMs in KTA patients, but markedly better in SPKT patients. Combined with Bayesian fitting, the model is very flexible since sampling times are not rigid and can be varied as long as dosing and sampling times are recorded accurately. The model has already proven to be clinically useful and is currently used to further investigate CsA in an integrated pharmacokinetic/pharmacodynamic model.

Objectives: The primary aim was to demonstrate that moxonidine, given in an experimental sustained release (SR) formulation, had no clinically relevant central nervous system (CNS) effects after 4 weeks of treatment. A clinically relevant CNS effect was predefined as more than 45 degrees s-1 reduction in saccadic peak velocity (SPV), corresponding to the effects of one night's sleep deprivation., Methods: In a randomized, double-blind fashion, 35 patients with mild to moderate essential hypertension received placebo run-in medication for 2 weeks, followed by 4 weeks' moxonidine sustained release (1.5 mg o.d.) or placebo. On the first day and 1 and 4 weeks following the start of treatment, blood pressure was measured and CNS effects were assessed using SPV, visual analogue scales and EEG., Results: On day 1 there was a significant, but not clinically relevant, reduction in the time-corrected area under the effect curve (AUEC) for SPV in the moxonidine group compared with placebo [difference of 38 degrees s-1; 95% confidence interval (CI) 23, 52]. This difference was no longer significant after one (9 degrees s-1; 95% CI -17, 35) and 4 weeks (6.9 degrees s-1; 95% CI -16, 30). Visual analogue scales for alertness showed similar results. A decrease in EEG alpha- and beta-power and an increase in delta-power were only found on day 1 of moxonidine treatment. The AUEC for systolic/diastolic blood pressure relative to placebo was 23 (95% CI 17, 29)/13 (9, 16) mmHg lower on day 1 and remained reduced by 20 (11, 30)/12 (6, 17) and 15 (6, 25)/9 (3, 15) mmHg after 1 and 4 weeks' moxonidine treatment., Conclusions: Four weeks' treatment with an experimental SR formulation resulted in tolerance to CNS effects (equivalence to placebo) while blood pressure-lowering effects remained adequate. The tolerance to CNS effects was already observed after 1 week of treatment.

This study investigates motilin effects on the proximal stomach in patients with functional dyspepsia (FD) and healthy volunteers. Eight healthy volunteers and 12 patients with FD were infused with synthetic motilin or placebo. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored by visual analog scales. Plasma motilin concentrations were measured by radioimmunoassay. Motilin concentrations and baseline gastric volumes were similar for patients and healthy volunteers. Motilin, compared with placebo, reduced gastric volume by 112 ml [F(29,195); confidence interval (CI) 95%] in patients and by 96 ml [F(-7,200); CI 95%] in healthy volunteers. In patients, motilin decreased compliance by 76 ml/mmHg [F(9,143); CI 95%] compared with placebo, which was similar in volunteers [66 ml/mmHg; F(11,120); CI 95%]. Patients were more nauseous during motilin compared with placebo (P = 0.04), whereas healthy volunteers did not experience nausea. We conclude that in a fasted condition, FD patients have a similar proximal gastric motor response to motilin as healthy volunteers, but experience an exaggerated sensation of nausea.

Nineteen healthy men received unilateral brachial artery infusions of either unfractioned heparin (0.3-100 IU/min), saline or the endothelium-dependent vasodilators substance P (2-8 pmol/min) and bradykinin (100-1000 pmol/min), and the endothelium-independent vasodilator sodium nitroprusside (2-8 micro g/min). Heparin caused a dose-dependent increase in plasma TFPI concentrations in both arms (ANOVA, p <0.0001). Estimated net forearm TFPI release was 7 +/- 16, 29 +/- 20 and 138 +/- 72 ng/100 mL tissue/min during 10, 30 and 100 IU/min of heparin respectively (ANOVA, p <0.0001). Compared to the systemic circulation, the forearm sensitivity to heparin induced TFPI release was 3.6-fold lower (166 +/- 67 ng/IU vs. 596 +/- 252 ng/IU: t-test, p = 0.004). Substance P, bradykinin and sodium nitroprusside all caused substantial dose-dependent increases in blood flow (ANOVA, p <0.001 for all) without affecting plasma TFPI concentrations. There are important regional differences in endothelial TFPI release, with the forearm circulation being relatively insensitive to heparin.

Binding of tissue plasminogen activator (t-PA) to the endothelium may be important in the prevention of thrombus formation. The aim was to develop a method to quantify endothelial binding in vivo. Nine healthy male volunteers received a 40 min continuous infusion with low dose recombinant t-PA (3.75 micrograms/min) and an indocycanine green infusion (0.5 mg/min) as control. A three-compartment recirculatory model was developed to account for non-specific circulatory delay effects. t-PA antigen, activity and t-PA/PAI-1 complex profiles showed a marked delay in increase at the beginning of the infusion. A reversible and concentration-dependent binding component was incorporated in the model which resulted in an accurate description of the t-PA concentration profile. t-PA binding was characterized by a dissociation constant of 5.9 ng/ml (SEM 1.8, CV 0%; fixed) and a binding capacity of 70 micrograms t-PA (SEM 10, CV 48%). This model can be used as a tool to quantify the ability of the endothelium to bind t-PA.

Aims: Heparin releases tissue factor pathway inhibitor (TFPI) from the endothelium and this release may decrease after repeated high dose heparin administration. The primary aim was to investigate and quantify this phenomenon during a short low dose heparin infusion. Also, the effects of heparin on tissue plasminogen activator (t-PA) were studied., Methods: Nine healthy, nonsmoking, male volunteers (range 19-23 years) received a continuous heparin infusion (2000 IU) over 40 min. The endothelial TFPI release rate was estimated from the total TFPI concentration profile using a pharmacokinetic model., Results: Mean +/- s.d. total and free TFPI increased from 62.9 +/- 9.4/8.3 +/- 2.1 ng ml-1 at baseline to 237.2 +/- 40.9/111.0 +/- 19.9 ng ml-1 after 40 min infusion. The relationship between heparin concentration (anti-IIa activity) and TFPI concentration followed a maximum effect model and a clockwise loop (proteresis) was observed. The TFPI release rate rapidly increased to maximum of 200 +/- 45 micro g min-1 after 17.5 min heparin infusion but did not increase further although heparin concentrations further doubled. In contrast to TFPI, t-PA antigen decreased from 5.6 +/- 1.0 at baseline to 4.5 +/- 1.0 ng ml-1 at the end of infusion (t = 40 min) (difference of 1.1 ng ml-1 (95% confidence interval; 0.9, 1.3)., Conclusions: Our application of concentration-effect models and pharmacokinetic principles to these haemostatic variables showed that endothelial TFPI release has a maximum that is already reached at low heparin dose, corresponding with an anti-IIa activity of 0.08 IU ml-1. The relationship between anti-IIa activity and TFPI release rate showed signs of acute tolerance (clockwise loop) indicating exhaustion of endothelial TFPI pools. These findings may be of importance for the heparin dose used in conditions such as unstable angina, in which the favourable effects of heparin have been ascribed to its ability to release TFPI.

Objectives: This study was designed to assess the concentration-effect relationships for the antihypertensive effects of rilmenidine in patients to aid in the design of an optimized concentration profile of a sustained-release formulation., Methods: A placebo-controlled, randomized, double-blind, 2-way partial crossover study was performed in subjects with hypertension. Patients were randomized to receive 2 of 3 possible 12-hour infusion regimens, each consisting of a loading phase (2 hours) and a maintenance phase (10 hours): low-profile infusion (total dose of rilmenidine, 1.45 mg), high-profile infusion (total dose, 3.3 mg), or placebo. Drug plasma concentrations, adverse events, blood pressure, heart rate, and visual analog scales were measured frequently, up to 24 hours after dosing. Salivary flow was determined for up to 15 hours., Results: The high concentration profile was well tolerated and continued to produce a significant blood pressure reduction of 10.4 mm Hg (systolic)/5.8 mm Hg (diastolic) after 24 hours. The low concentration profile showed no significant effects on blood pressure compared with placebo after 24 hours. Decreases in salivary flow were -36% for the high-profile infusion and -20% for the low-profile infusion compared with placebo. Pharmacokinetic-pharmacodynamic analyses showed infusion rate-independent, linear concentration-dependent reductions in diastolic blood pressure and salivary flow up to the maximum observed rilmenidine concentration for both types of infusion., Conclusions: The high concentration profile was well tolerated and still produced a significant blood pressure reduction after 24 hours. Pharmacokinetic-pharmacodynamic relationships were linear and unaffected by the rate of infusion. These results should aid in the design of an optimal slow-release profile.

Purpose: To study the dexamethasone concentration in aqueous humor, vitreous, and serum of patients after repeated topical application of dexamethasone disodium phosphate., Design: Prospective nonrandomized comparative trial., Participants: Twenty phakic patients scheduled for a first vitrectomy., Methods: All participants received dexamethasone disodium phosphate drops according to an application schedule intended to result in steady-state drug concentrations. Starting on the preoperative day, they received 1 drop of dexamethasone disodium phosphate (0.1%) every 1 hours until the time of vitrectomy (total, 10 or 11 drops). At night, ointment containing dexamethasone (0.3 mg/g) and gentamicin (5 mg/g) was administered once. From 7 AM on, the drop application schedule was resumed. At the start of the vitrectomy, samples were taken from the aqueous humor, vitreous, and blood., Main Outcome Measures: The dexamethasone concentrations in the aqueous humor, vitreous, and serum measured by radioimmunoassay., Results: The mean dexamethasone concentrations in the aqueous humor, vitreous, and serum were 30.5 ng/ml (range, 7.1-57.7; standard deviation [SD] 15.0), 1.1 ng/ml (range, 0.0-1.6; SD 0.4), and 0.7 ng/ml (range, 0.0-1.2; SD 0.4), respectively., Conclusions: Compared with previously tested administration routes (peribulbar or subconjunctival injection or oral administration), the penetration of dexamethasone into the vitreous after repeated drop application is negligible. Despite the frequent dosing schedule, the dexamethasone concentration in the aqueous humor is far lower than after a subconjunctival injection with dexamethasone disodium phosphate. Systemic uptake is low.

Background: The optimal dosing strategy for continuous intravenous furosemide infusion is unknown in pediatric patients. Eighteen patients less than 1 year old were studied after cardiac surgery during routine clinical care. The current strategy starts with a continuous infusion of 0.1 mg/kg x h, which may be adapted., Methods: A pharmacokinetic-pharmacodynamic model was developed that linked furosemide dose to furosemide serum concentrations, renal function (creatinine clearance), and urine output. Various regimens were simulated that adapt according to urine production. The modified dosing schedule was prospectively tested in a subsequent population of 18 pediatric patients after cardiac surgery., Results: Data from the follow-up study suggest that urine production is more controlled for the proposed regimen., Conclusions: Both the modeling and simulation results and the follow-up study indicated that a bolus dose of 1 mg/kg followed 6 hours later with a 1- or 2-mg/kg loading dose and a 0.2-mg/kg x. h intravenous infusion provides a rational starting point for furosemide therapy after cardiac surgery in pediatric patients less than 1 year old. Adjustment of this regimen every 12 hours in steps of 0.1 mg/kg x h on the basis of clinical assessment should lead to adequate control over urinary output.

Abdominal obesity is associated with reduced 24-h plasma GH concentrations. It is unclear whether hyposomatotropism in abdominally obese humans is compensated by up-regulation of GH receptor sensitivity or causes less biological effect in target tissues. We, therefore, determined the responsiveness of adipose tissue to the lipolytic action of GH in abdominally obese (OB) and normal weight (NW) postmenopausal women. An iv bolus of recombinant human GH or placebo was randomly administered to eight NW [body mass index (BMI): 22.2 +/- 1.6 kg/m(2)] and eight abdominally OB (BMI: 32.1 +/- 2.6 kg/m(2)) women. Lipolysis was measured by infusion of D5-glycerol and modeled as a function of plasma GH concentrations to describe adipose tissue responsiveness. Similar plasma GH concentration peaks ( approximately 20 mU/liter) were achieved by GH injection in both groups. During placebo conditions, the average plasma GH level was significantly lower in OB compared with NW women (0.74 +/- 0.52 vs. 2.08 +/- 1.18 mU/liter, P = 0.023). Adipose tissue responsiveness, expressed as glycerol rate of appearance per kilogram of fat mass per unit plasma GH concentration was not different in both groups (NW: 1.06, OB: 0.68, P > 0.05). These results suggest that hyposomatotropism in abdominally obese individuals is not compensated by increased adipose tissue responsiveness to GH bio-action and, therefore, blunts lipolysis in these individuals.

Nonlinear mixed effects modeling (NONMEM) and nonparametric expectation maximization (NPEM2) have both been used in population modeling of tobramycin. We compared both methods for differences in population pharmacokinetic parameters in relation to error models used. Predictive performance was compared between models. A group of 470 neonates who had received tobramycin according to a gestational age (GA)-dependent dosing interval was analyzed according to a one-compartment model with NONMEM and NPEM2. Additional models were constructed where the assay error pattern in NPEM2 mimicked NONMEM residual error and vice versa. Individual pharmacokinetic parameter estimates were compared. Predictive performance was evaluated in a separate group of 61 patients. Population estimates and variation coefficients (CV) for optimal models were NONMEM K(el) 0.071 h(-1) (27%), V(d) 0.59 L/kg (9%); NPEM2 K(el) 0.079 h(-1) (42%), V(d) 0.65 L/kg (48%). Forcing NONMEM to use the NPEM2 error pattern as residual error or vice versa resulted in smaller differences in CVs of the estimates. NONMEM gave less bias (P < 0.05) than NPEM2 and comparable precision with this approach. In conclusion NONMEM and NPEM2 are dissimilar in population estimates. Differences in ranges of pharmacokinetic parameter estimates between NONMEM and NPEM2 are largely determined by the method of incorporating error patterns in both programs.

Objective: Our objective was to individualize tobramycin dosing regimens in neonates of various gestational ages with use of early therapeutic drug monitoring., Methods: This study was performed in neonatal patients with suspected septicemia in the first week of life. All patients received tobramycin, 4 mg/kg per dose, as a 30-minute intravenous infusion, with a gestational age-related initial interval of 48 hours (<32 weeks), 36 hours (32-36 weeks), and 24 hours (> or =37 weeks). The target serum peak and trough serum concentrations were 5 to 10 mg/L and 0.5 mg/L, respectively. Serum trough samples and 1- and 6-hour samples were taken after the first dose. Tobramycin concentrations were used to obtain gestational age-dependent population models with nonparametric expectation maximization software. To investigate the effect of timing of sampling in a second group of patients, serum trough samples and 3- and 8-hour samples were taken after the first dose of tobramycin was administered. Serum trough concentrations were predicted by use of linear pharmacokinetics in both groups and by use of the population models with bayesian feedback of 1 or 2 serum concentrations in the second group. These predicted concentrations were compared with actual serum trough concentrations. The predictive performance of the 1- to 6-hour and 3- to 8-hour models and the population models were compared with a gestational age-related model without therapeutic drug monitoring., Results: A total of 247 patients were analyzed: 206 with 1- to 6-hour serum samples and 41 with 3- to 8-hour serum samples. Peak serum concentrations were above 5 mg/L in 90.8% of cases, and trough serum concentrations were above 1 mg/L in 25.5% of cases. The 3- to 8-hour linear model had a bias of -0.31 mg/L and a precision of 0.48 mg/L, and it performed significantly better than the 1- to 6-hour model. The best nonparametric expectation maximization model had a bias of -0.11 mg/L and a precision of 0.45 mg/L. None of the models yielded a significant improvement of predictive performance over the model without therapeutic drug monitoring., Conclusions: Routine early therapeutic drug monitoring does not improve the model-based prediction of initial tobramycin dosing intervals in neonates in the first week of life.

Lipolysis (the breakdown of fat) is generally estimated using stable isotopes, where the rate of appearance (Ra) of glycerol is calculated using Steele's equations. These equations are based on single-compartment differential equations for tracer and tracee where rate of change is approximated by the change in concentration from one time point to the next. We demonstrate an alternative approach to estimate metabolic processes, and to determine relationships between hormones and their actions. Growth hormone (GH) or saline was administered in a double-blind randomized crossover design to eight normal weight (NW) and eight obese (OB) subjects, and differences in the effects of GH on lipolysis were investigated. The relationship between the plasma GH concentration and glycerol Ra (as an index of lipolysis) was described using PK/PD modeling. The model incorporated the plasma GH, glycerol and D5-glycerol concentration profiles, and two sequential effect compartments to account for the delay in response. The estimated time-profile of glycerol Ra was compared with estimates obtained using Steele's equations. NONMEM (Version V) FOCE was used for parameter estimation, four differential equations were used, and glycerol and D5-glycerol were estimated simultaneously. The model adequately described both primary variables (glycerol) and derived variables (glycerol Ra as obtained using Steele's equations). Modeling allowed the assessment of potential differences in GH sensitivity in the two groups, and indicated the importance of GH in lipolysis.

Single-dose administration of 5-hydroxytryptophan (5-HTP) is regularly used as a challenge test of the serotonergic system. The use of 5-HTP has been limited by an apparent small window between the occurrence of neuroendocrine endpoints and the occurrence of side effects. Therefore, many dosing strategies have been tried with and without concurrent administration of carbidopa, a peripheral inhibitor of the decarboxylation from 5-HTP to serotonin. The aim of the current study was to assess the relation between pharmacokinetics and pharmacodynamics of 5-HTP. Twelve healthy male volunteers were included in a placebo-controlled, randomized, four-way crossover, double-blind, single-dose investigation of oral 5-HTP with or without coadministration of carbidopa. The four dose regimens were placebo, 5-HTP 100 mg, 5-HTP 200 mg, and 5-HTP 100 mg with coadministration of carbidopa 100 mg and 50 mg at 3 hours before and 3 hours after the administration of 5-HTP, respectively. The last regimen resulted in a doubling of the elimination half-life, an apparent clearance at least 14 times smaller, and a 15.4 times greater area under the curve compared with 5-HTP 100 mg without carbidopa. Furthermore, it was the only regimen to induce a significant change in cortisol and prolactin. It did not induce any change in subjective psychologic symptoms or cardiovascular parameters, but it was the only regimen to induce some nausea in three participants. The authors conclude that this regimen of 5-HTP 100 mg plus carbidopa is a relatively simple, effective, and tolerable challenge of the presynaptic serotonergic system. Further increase of the dose of 5-HTP might improve the size of the effect on endpoints as long as the tolerability remains good.

Unlabelled: We previously reported that a single dose of the serotonin receptor agonist meta-chlorophenylpiperazine increased the peak velocity of saccadic eye movements and decreased low-frequency electroencephalographic activity., Methods: We administered a single dose of the serotonin releaser dexfenfluramine in a double blind, placebo controlled randomised cross-over design and measured saccadic eye movements and EEG every hour up to 6 h. Subjects were 62 males (18-30 years) with a history of no, moderate or heavy use of ecstasy tablets., Results: Dexfenfluramine increased saccadic peak velocity and decreased alpha, delta and theta electroencephalographic activity, the latter predominantly in heavy users of ecstasy., Conclusions: This study supports the idea that saccadic peak velocity and EEG can be useful endpoints of a serotonergic challenge. This could be an important anatomical extension of these end-points, which until now were limited to the effect on hypothalamic serotonergic projections., (Copyright 2002 John Wiley & Sons, Ltd.)

Objective: Patients undergoing major orthopaedic surgery who are being treated with fondaparinux sodium for prevention of venous thromboembolism may be receiving treatment for coronary artery disease or chronic inflammatory disease of the joints or arthritis. Two separate studies assessed any possible interaction between fondaparinux sodium at steady state and aspirin (acetylsalicylic acid) or piroxicam in healthy volunteers., Design: In the first study a single dose of aspirin 975mg was assessed initially, followed by single doses of aspirin or placebo on the fourth day of an 8-day regimen of subcutaneous fondaparinux sodium (10mg once daily). The second study was a three-way crossover, double-blind, randomised study which investigated fondaparinux sodium 10mg + placebo, fondaparinux sodium 10mg + piroxicam 20mg, or placebo + piroxicam 20mg., Methods: Both studies obtained plasma concentration-time profiles of fondaparinux sodium administered alone and with aspirin or piroxicam. Noncompartmental parameters - peak concentration, trough concentration, time to reach peak concentration, and area under the concentration-time curve - were obtained. Both studies measured the pharmacodynamic parameters bleeding time and activated partial thromboplastin time (aPTT). Safety was monitored., Results and Conclusions: Neither aspirin nor piroxicam influenced the pharmacokinetics of fondaparinux sodium at steady state. Two hours after administration, prolongation of bleeding time with aspirin alone or with aspirin plus fondaparinux sodium was significantly greater than with fondaparinux sodium alone (p = 0.003 and p = 0.004, respectively). No significant differences were observed between aspirin alone or aspirin + fondaparinux sodium in effect on bleeding time. A small decrease in collagen-induced platelet aggregation was observed after administration of piroxicam alone or piroxicam + fondaparinux sodium. A small effect on aPTT was observed; it was similar for fondaparinux sodium whether administered alone or in combination with either aspirin or piroxicam. No serious adverse events were reported.

The valid measurement of the concentration of serotonin (5-HT) in blood plasma is important when using the platelet as a model for the serotonergic neuron. The assay is hampered by the release of 5-HT by (residual) platelets during the preparation for assay. We developed an isopycnic method that separates cells gently and completely from plasma by centrifuging a diluted Percoll density-gradient to which whole blood was added. In this study this method was compared with the usual differential centrifugation method. The isopycnic method on average resulted in nine times lower levels of plasma 5-HT. This difference was linearly related to the number of residual platelets in plasma after differential centrifuging. The proportion of intra-individual variation decreased three-fold. Therefore, the use of a Percoll density-gradient may lead to a more precise and more accurate estimate of the level of plasma 5-HT. Copyright 2000 John Wiley & Sons, Ltd.