The absolute systemic availability of a new oral formulation of co-dergocrine in healthy subjects

Summary We have studied the absolute systemic availability (f) of an oral formulation (Hydergin spezial = Hydergine FAS^R 4 mg per tablet) of codergocrine by three different methods.Twelve healthy volunteers received single doses of 0.9 mg co-dergocrine intravenously and 8.0 mg orally in a randomized crossover design. The pharmacological effect of co-dergocrine was monitored as a reduction in plasma prolactin.Maximal plasma concentrations of co-dergocrine after oral dosing ranged between 0.181 and 1.307 ng·ml^–1. Maximal urinary excretion ranged between 4.7 and 9.9 µg·h^–1 and between 0.3 and 2.3 µg·h^–1 after intravenous and oral doses respectively. Clearance was measured as 90±22 l·h^–1 and the absolute systemic availability (f) as 2.25±0.65% by using the areas under the plasma concentration-time curves extrapolated to infinity. Calculation of f by comparing areas up to 32 h or the fractions of the dose excreted in urine led to identical results.The intravenous and oral doses produced similar pharmacological effects (reduction of plasma prolactin concentrations) despite the small value of f.     

Pharmacokinetics of methadone and its primary metabolite in 20 opiate addicts

In a closed metabolic ward the pharmacokinetics of methadone and its primary metabolite (EDDP) were studied in 20 long-term opiate addicts. After administration of the daily oral dose of methadone HCl (mean 60 mg, range 10–225 mg) blood samples were taken and analysed, using a newly developed high-performance liquid chromatography (HPLC) method. The steady-state plasma concentrations of the 20 subjects varied from 65–630 ng·ml^–1 and from 5 to 55 ng·ml^–1, whereas the peak concentrations were 124–1255 ng·ml^–1 and 10 – 301 ng·ml^–1 for methadone and EDDP, respectively. The calculated ratios between the area under the curve (AUC_{(0–24 h)}) for methadone and the AUC_{(0–24 h)} for EDDP varied from 5.9 to 44.6, indicating interindividual differences in metabolic activity. In 19 out of 20 subjects the pharmacokinetics of methadone are best described using a two-compartment model. The mean body clearance was 1.64 ml·min^–1·kg^–1, whereas the mean elimination rate constant () and plasma half-life (t _1/2) were 0.026·h^–1 (range 0.013–0.053·h^–1) and 31.2 h (range 13–53 h), respectively. Differences of gender were also found. A poor correlation was found between the methadone dose and the steady-state level. A much better correlation was found between the normalized steady-state level and the body clearance.     

Steady-state kinetics of doxepin and imipramine in Saudi patients with interethnic comparison

The pharmacokinetics of doxepin (DX) was studied in 21 Saudi patients treated long term with oral doses of this tricyclic antidepressant agent. The mean (SEM) values of the dose-normalized steady-state concentration and the apparent clearance after oral administration of this drug were 25.8 (4.8) ng·ml^-1/mg·kg^-1 and 2.529 (0.342) l·h^-1·kg^-1, respectively. The pharmacokinetics of impramine (IMI) was also studied in 30 Saudi patients who received oral doses of this drug for long durations. The mean dose-normalized steady-state concentration of IMI was 68.3 (19.7) ng·ml^-1/mg·kg^-1, and the mean apparent clearance after oral administration of IMI was 1.619 (0.353) l·h^-1·kg^-1. The mean (SEM) ratio of the steady-state concentration of the metabolite desipramine (DES) to that of IMI (DES/IMI) was 0.873 (0.151). Using this value and the ratio of the mean apparent clearance after oral administration (TCL) of DES to that of IMI, the fraction of IMI metabolized to DES was calculated to be 0.489. The TCL of DES was estimated from data obtained for three additional patients who received oral doses of this drug for long durations. A mean value of 0.907 (0.351) l·h^-1·kg^-1 was obtained.     

Investigation of nimodipine pharmacokinetics in Chinese patients with acute subarachnoid haemorrhage

Summary Nimodipine pharmacokinetics was investigated in 12 Chinese patients with acute subarachnoid haemorrhage receiving an IV infusion of 1.6 or 2 mg/h (based on estimated body weight) for 10 days. Peripheral venous blood samples were collected for up to 4 days and plasma nimodipine was assayed by GC/ECD. The mean value was taken as the steady state concentration (C_ss) and Clearance (CL) (hourly dose/C_ss) was calculated. Eight survivors were given oral nimodipine (60 or 90 mg) every 6h (based on body weight), blood was sampled over 6 h and the plasma nimodipine level determined. The values for C_ss, CL and CL·kg^–1 were 33.5 g·l^–1, 58 l·h^–1 and 1.0 l·h^–1·kg^–1 respectively; in survivors receiving the drug orally, bioavailability of the 30 mg tablet was 9%. In one very sick patient given crushed tablets by naso-gastric tube, the AUC was very low; in vitro studies indicated that adsorption of nimodipine by the tubing was unlikely to have been the cause.The pharmacokinetic findings in Chinese patients are comparable to previously reported values in Caucasians.     

Alteration by burn injury of the pharmacokinetics and pharmacodynamics of cimetidine in children

Summary We have studied the mechanisms of the increased dosage requirements of the H₂-receptor antagonist cimetidine in paediatric burned patients in a pharmacokinetic and pharmacodynamic study.Cimetidine (10–15 mg·kg^–1) was given to 21 burned children and multiple blood samples were obtained for determination of plasma cimetidine concentrations and pharmacokinetic analysis.The relation of gastric pH to plasma cimetidine concentrations was studied in five of these children who had nasogastric tubes. In an additional four patients the effects of cimetidine on gastric pH were studied during a continuous infusion of cimetidine, which maintained steady-state plasma cimetidine concentrations above 0.5 µg·ml^–1.The mean (SEM) clearance of cimetidine in burned children was 16.22 ml·kg^–1 and cimetidine half-life was 1.06 h. The cimetidine clearance and half-life values were significantly higher in burned children compared with our previously reported values for normal adult patients, 8.2 ml·min·kg^–1 and 2.21 h respectively.Endogenous creatinine clearance normalized to 70 kg in burned children was 190 ml·min^–1. In burned children 41% of the dose of intact cimetidine was excreted during 8 h of the study compared with 45% excretion during 24 h in healthy adult controls previously reported. The correlation coefficient between creatinine and cimetidine clearances was 0.93 (r ²=0.85).The plasma concentration of cimetidine needed to increase gastric pH to 4.0 was 1.0 µg·ml^–1, which contrasts with the value of >0.5 µg·ml^–1 required for adult burned patients.These findings support the hypothesis that the higher dosage requirements of cimetidine in burned children is due both to enhanced elimination kinetics and to alterations in target organ sensitivity, requiring higher than normal plasma concentrations for the desired effect. In burned children Cimetidine should be given in higher doses and/or more frequently.     

Hepatic enzyme induction and vitamin K1 elimination in man

Summary We have studied the single dose and steady-state pharmacokinetic of tiaprofenic acid in ten elderly arthritic patients living in the community (5 men and 5 women) taking 200 mg tid for 8 days.The mean area under the plasma concentration-time curves to 8 h (AUC (0–8)) did not alter significantly from day 1 to day 8 (77.25 to 79.61 µg·ml^–1. h). The mean terminal phase half-life (t_1/2) was 2.05 h and 2.25 h on Days 1 and 8 respectively in patients in whom the calculations were possible (7 patients on Day 1 and 6 patients on Day 8). The median observed time of maximum concentration (t_max) and the mean observed maximum plasma concentration (C_max) of 100 min and 21.3 µg·ml^–1 respectively on Day 1 were not significantly different from the values obtained on Day 8 (t_max 120 min; C_max 20.7 µg·ml^–1). The kinetic data suggest that there should be no significant accumulation of tiaprofenic acid in elderly ambulant people suffering from arthritis.     

Development of a population pharmacokinetic database for tianeptine

Summary Two thousand three hundred and thirty five plasma concentrations of tianeptine from 112 patients enrolled in nine studies of tianeptine pharmacokinetics performed prior to the marketing of the drug were pooled for analysis using mixed-effect modeling. Studies represented a combination of single dose and multiple dosing at steady-state. Tianeptine plasma concentration time data were fit to a two compartment model with first order absorption using the NONMEM computer program.The results of this analysis suggested that alcoholism is associated with significant increase in clearance (124% increase) and volume of the central compartment (161% increase). The volume of the peripheral compartment is significantly lower in women (31% decrease) and in depressed patients (59% decrease).The population mean (interindividual variability) clearance was equal to 0.17 l·h^–1·kg^–1 (28.6%), the volume of central compartment was 0.13 l·kg^–1 (60.4%), intercompartmental clearance was 0.07 l·h^–1·kg^–1 (30.1%), volume of the tissue compartment was 1.17 l·kg^–1 (28.3%), and the absorption rate constant was 0.63 h^–1 (21.8%). The residual variability was approximately 30% at concentrations expected during clinical use of the drug.Because of the increased clearance, alcoholic patients would be expected to have significantly reduced concentrations during steady-state dosing. These population parameters provide a basis for developing initial dosing recommendations and for performing bayesian evaluations of drug concentrations obtained in post-marketing studies.     

Total and free steady-state plasma levels and pharmacokinetics of nifedipine in patients with terminal renal failure

Summary The total and free steady-state plasma levels of nifedipine in patients with renal failure have been compared with those in subjects with normal renal function. Studies were done after administration of nifedipine 10 mg t.d.s. p.o. for 5 days, after i.v. infusion of 4·4 mg, and after a single 10 mg oral dose.The systemic clearance of nifedipine after a single i.v.-dose was higher in subjects with renal insufficiency (854 ml/min) than in those with normal renal function (468 ml/min). After the single oral dose the AUC (6100 ng·min·ml^–1) and maximum plasma concentration (75.0 ng·ml^–1) were lower than in subjects with normal renal function (19300 ng·ml^–1; 122 ng·ml^–1). The plasma protein binding of nifedipine averaged 95.5% in normal subjects and 94.8% in patients with renal failure.Although free and total steady-state plasma levels of nifedipine tended to be somewhat lower than normal in renal failure, the changes in pharmacokinetics and decreased protein binding of nifedipine did not result in a significantly different steady-state plasma level of the drug. The blood pressure response to a given plasma nifedipine level appeared to be enhanced in renal failure.     

The pharmacokinetics of amiloride-hydrochlorothiazide combination in the young and elderly

Summary The pharmacokinetics of amiloride and hydrochlorothiazide were studied in 12 healthy young volunteers following a single dose of a fixed combination of amiloride and hydrochlorothiazide and in 11 elderly hypertensive patients at steady-state. Following modelling of the single dose data, simulated steady-state plasma concentrations for the 2 drugs were generated to examine the effect of age and/or hypertension on pharmacokinetics.The apparent systemic plasma clearance for both amiloride and hydrochlorothiazide was significantly reduced in the elderly when compared to the young (from 753 to 325 ml·min^–1, amiloride; and from 418 to 157 ml·min^–1, hydrochlorothiazide). The plasma concentrations at steady state for both drugs were greatly increased in the elderly patients (Amiloride: from 7 to 25 ng·ml^–1, C_ss,max; from 2 to 8 ng·ml^–1, C_ss,min; and from 4 to 14 ng·ml^–1, C_av; Hydrochlorothiazide: from 184 to 651 ng·ml^–1, C_ss,max; from 31 to 121 ng·ml^–1, C_ss,min; and from 89 to 273 ng·ml^–1, C_av).The decreased clearance of the diuretics in the elderly was believed due to deterioration of renal function, and there was a significant correlation between the plasma clearance of hydrochlorothiazide and creatinine clearance in both age groups (r=0.62, young;r=0.72, elderly).As a result of the pharmacokinetic findings caution may be indicated in the clinical dosage of the diuretics particularly when in fixed dose combination.     

Single-dose and steady-state pharmacokinetics of sabeluzole in senile dementia of Alzheimer type patients

Summary The single- and repeated-dose pharmacokinetics of sabeluzole have been determined in six elderly patients with [senile] dementia of the Alzheimer type.After a single oral dose of 10 mg sabeluzole, the peak plasma concentration was attained at 1 to 4 h; it averaged 42 ng·ml^–1. On repeated dosing (10 mg b. d.), steady-state was virtually attained after 3 days of treatment. Steadystate mean trough and peak plasma concentrations fluctuated between 53 and 94 ng·ml^–1. The mean terminal half-life after a single dose and at steady-state was of the order of 33 h.Sabeluzole was well tolerated and at the end of treatment, no systematic changes in blood haematology, biochemistry or urinalysis were seen.     

Pharmacokinetics of oral salbutamol controlled-release in Asian patients with asthma

Summary Using a double blind, double dummy crossover design, single dose and steady state pharmacokinetics of oral controlled release (SCR) salbutamol 4 mg and 8 mg tablets b. d. has been studied in 8 Asian patients.Plasma salbutamol was measured over 12 h. In 8 patients the single dose mean C_max was 4.2 ng·ml^–1 and 7.7 ng·ml^–1 after 4 and 8 mg, respectively. In 5 patients the steady state mean C_max, C_min and t_max were 8.1 ng·ml^–1 and 4.7 ng·ml^–1 and 6 h for the 4 mg tablets and 14.1 ng·ml^–1 and 7.1 ng·ml^–1 and 4 h for the 8 mg tablets.It is concluded that both doses of SCR show features of controlled release and that they produced a relatively constant plasma level of salbutamol in Asian patients.     

Growth hormone-releasing activity of hexarelin in humans

Hexarelin is a new hexapeptide (His-d-2-methyl-Trp-Ala-Trp-d-Phe-Lys-NH₂) that stimulates the release of growth hormone both in vitro and in vivo. In this double-blind, placebo-controlled, rising-dose study we evaluated the growth hormone releasing activity of hexarelin in healthy human subjects. Twelve adult male volunteers received single intravenous boluses of 0.5, 1 and 2 ·g·kg^–1 hexarelin as well as placebo. For safety, drug doses were given in a rising-dose fashion with placebo randomly inserted into the sequence. Plasma growth hormone concentrations increased dose-dependently after the injection of the peptide, peaking at about 30 min and then decreasing to baseline values within 240 min with a half-life of about 55 min. The mean peak plasma growth hormone concentrations (C_max) were 3.9, 26.9, 52.3, 55.0 ng·ml^–1 after 0, 0.5, 1 and 2 g·kg^–1, respectively. The corresponding areas under the curve of growth hormone plasma levels from drug injection to 180 min (AUC_0–180) were 0.135, 1.412, 2.918 and 3.695 g·min·ml^–1. The theoretical maximum response (E_max) and the dose that produces half of the maximum response (ED₅₀) were estimated using logistic regression. The calculated ED₅₀ values were 0.50 and 0.64 g·kg^–1 for C_max and AUC_0–180, respectively. The corresponding E_maxs were 55.1 ng·ml^–1 and 3936 ng·min·ml^–1, thus indicating that the effect after the 2 g·kg^–1 dose is very close to the maximal response. Plasma glucose, luteinising hormone, follicle-stimulating hormone, thyroid-stimulating hormone and insulin-like growth factor I were unaffected by hexarelin administration, while the peptide caused a slight increase in prolactin, cortisol and adrenocorticotropic hormone levels. Hexarelin was well tolerated in all subjects. The results of this study indicate that intravenous administration of hexarelin in man produces a substantial and dose-dependent increase of growth hormone plasma concentrations.     

Pharmacokinetics of naproxen in elderly patients

Summary The pharmacokinetics of naproxen have been examined in 13 elderly patients (mean age 84.2 years) and in 9 younger patients (mean age 53.9 years) at the end of a 21 day course of therapy with naproxen 500 mg b.d. The mean pre-dose concentration on days 19, 20 and 21 was significantly higher in the elderly patients than in the controls (60.1 vs. 43.3 µ g · ml^–1). The AUC (0–24) was significantly higher in the elderly subjects only when normalized for body weight (9.1 vs. 5.4 µg·ml^–1·h kg^–1 p0.02). The AUC was significantly higher in the elderly group compared to the control group also in the normalized form. The apparent clearance of naproxen was reduced in the elderly compared to the control patients (315 vs. 628 ml·h^–1). The percentage protein binding of naproxen was the same in both groups (99.8%) but the free concentration of naproxen was significantly higher in the elderly patients than in the control patients (141 vs. 89.8 ng·ml^–1). Although there was no excess of side effects in the elderly patients it is suggested that when naproxen is given to elderly patients, therapy should be started at the lower end of the dosage range.     

The pharmacokinetics of ceftriaxone and cefotaxime in cirrhotic patients with ascites

Summary We have compared in two separate studies the kinetics of ceftriaxone and cefotaxime in 8 cirrhotic patients with ascites and 8 control subjects after a single 20 min intravenous infusion of 1 g of each drug.The apparent volumes of distribution (V_z) were found to be significantly higher in cirrhotics than in control subjects (0.87, versus 0.49, l·kg^–1, for cefotaxime and 0.23 versus 0.13 for ceftriaxone).The elimination kinetics of ceftriaxone were similar in the two groups. In contrast, the total and non-renal clearances of cefotaxime were reduced in cirrhotic patients.The two drugs rapidly entered the ascitic fluid. Peritoneal concentrations of ceftriaxone were higher than 7 µg·ml^–1 from the second hour after the infusion and were 8.9 µg·ml^–1 at 24 h. Peritoneal concentrations of cefotaxime were higher than 4 µg·ml^–1 from 0.5 to 8 h after the infusion.     

Effect of 6-hourly intermittent intravenous boluses of oxmetidine and ranitidine on gastric acidity and serum prolactin

Summary We have measured the plasma concentrations of captopril and total disulfide conjugates of captopril after a 50 mg oral dose in 6 uraemic patients on maintenance dialysis and in 8 hypertensive subjects with normal renal function.The mean peak plasma concentration of captopril was 2.5 times higher (0.447 µg·ml^–1 vs 0.181 µg·ml^–1) and the concentrations of the disulfides 4 times higher (3.62 µg·ml^–1 vs 0.924 µg·ml^–1) in the uraemic patients. Moreover captopril disulfide conjugates in the uraemic subjects reached peak concentrations at 8 h after the dose and subsequently felt. The apparent plasma half-time was 46±19 h. Only 15% of these conjugates were removed by dialysis.This marked accumulation of captopril conjugates was associated with a sustained fall in both systolic and diastolic blood pressures. In uraemic patients the mean maximum reduction in systolic and diastolic blood pressures were 37±7 mmHg and 24±9 mmHg respectively, occurring 6 h after the dose, compared with 8±7 and 8±1 mmHg respectively at 30 min in normal renal function patients. These results are consistent with the results of animal experiments, which show that captopril disulfides can be converted back to free captopril and can contribute to the antihypertensive effect of the drug. They provide a reationale for reducing the dose and frequency of administration of captopril in patients with significant renal impairment.     

Studies on hydralazine

Summary After oral administration of a single 50 mg dose of hydralazine (Apresoline^®), the serum half-life (T1/2) and bioavailability (AUC_0–) were assessed in 16 healthy volunteers. The half-life was 2.57±0.14 h (S.E.) in 10 slow acetylators of sulphadimidine, and 2.18±0.15 h in 6 fast acetylators (difference not statistically significant). AUC_0– was significantly higher in slow acetylators, at 1.04±0.10 µg·hour·ml^–1, compared to 0.66±0.12 µg·hour·ml^–1 in the fast acetylators (p<0.025). Treatment with Apresoline^® 25 mg tid produced minimum serum concentrations at steady-state of 57.3±7.3 ng·ml^–1 and 33.4±4.2 ng·ml^–1 in 8 slow and 5 fast acetylators, respectively (p<0.05). The corresponding maximum concentrations were 228.8±20.3 ng·ml^–1 and 147.6±15.0 ng·ml^–1 in slow and fast acetylators, respectively (p<0.025). First-pass metabolism of hydralazine could explain the difference in bioavailability of the drug between fast and slow acetylators, without any corresponding difference in the elimination rate of the drug in the post-distributive phase.     

Evaluation of a proposed method for phenytoin maintenance dose prediction following an intravenous loading dose

Summary A large clinical study, designed to investigate the induction of theophylline metabolism by phenytoin, provided the opportunity to test a previously proposed method for estimating dose requirements of phenytoin. This method involves prediction of the oral maintenance dosage from data obtained following the administration of an intravenous loading dose.In 30 subjects, trough plasma concentration at steady-state were 12.0±4.9 µg·ml^–1 (mean ±SD) and differed by –2.7±39.3% from a mean target plasma concentration of 12.5±1.5µg·ml^–1.A Bayesian regression programme was used to forecast an estimate of each subject's individual pharmacokinetics. These were then used to predict the steady-state plasma concentrations which would be expected from a standard dosing regimen (4 mg per kg per day). When compared to the results expected from the use of this standard dosage, the proposed method gave acceptable steady-state plasma phenytoin concentrations with significant reductions in deviations from target concentrations.This method for the rapid individualization of phenytoin dosage requirements provides an improvement over more traditional methods of choosing an arbitrary dose adjusted for body weight followed by dosage adjustments based on achieved plasma concentration.     

Single dose pharmacokinetics of proguanil and its metabolites in pregnancy

Summary Plasma and whole blood concentrations of proguanil, its active metabolite cycloguanil, and the inactive metabolite 4-chlorophenyl-biguanide, were measured by HPLC in 10 healthy Karen women in the last trimester of pregnancy, following a 200 mg single oral dose of proguanil. Four of these women were restudied 2 months after delivery.The pharmacokinetic properties of proguanil were similar during and after pregnancy. Median peak plasma concentrations of proguanil during pregnancy and following delivery were 212 and 215 ng·ml^–1, and occurred at 4.5 and 5 h, respectively. Mean plasma AUC values for proguanil during and following pregnancy were 94 and 98 ng·h·ml^–1·kg^–1, respectively. Corresponding whole blood AUC values were 361 and 396 ng·h·ml^–1·kg^–1. The mean elimination half lives and mean residence times of proguanil in plasma and whole blood were 12.3 and 19.6 h and 13.8 and 20.7 h respectively during pregnancy. Following pregnancy these values were 17.1 and 19.7 h for plasma and 19.7 h and 20.2 h for whole blood respectively.Mean peak plasma and whole blood concentrations of cycloguanil following pregnancy were 25 and 22 ng·ml^–1 respectively. During pregnancy peak cycloguanil concentrations in both plasma and whole blood were markedly lower, 13 and 12 ng ml^–1, respectively. Two pregnant women (neither of whom were restudied) were probably poor metabolisers of proguanil. The mean ratio of proguanil to cycloguanil plasma AUC was 16.7 in the third trimester of pregnancy and 7.8 following pregnancy, compared with less than 5 in previously reported studies. The concentrations of 4-chlorophenylbiguanide in both plasma and whole blood in pregnant subjects were also lower than those after pregnancy.These data show that blood concentrations of the active antimalarial metabolite cycloguanil are reduced in late pregnancy and that the currently recommended dose of proguanil could be inadequate for antimalarial prophylaxis in pregnant women.     

Concentrations of ciprofloxacin in human liver,gallbladder, and bile after oral administration

Summary We have measured concentrations of ciprofloxacin in serum, hepatic tissue, gallbladder, and bile in 10 patients after a single oral dose of 750 mg given before cholecystectomy. Mean liver and gallbladder tissue concentrations were 12.76 µg·g^–7±2.79 (SEM) and 5.94 µg·g^–1±1.35, respectively. Concentrations in bile taken from the gallbladder (7 patients) ranged from 68 to 225 µg·ml^–1, with a mean bile/serum concentration ratio of 49. Concentrations in bile taken from the common bile duct (2 patients) were 17 and 16 µg·ml^–1.     

Pharmacokinetic and pharmacodynamic modelling with pancuronium

Summary The pharmacokinetics and pharmacodynamics of pancuronium were studied following intravenous infusion in eleven patients undergoing surgical anaesthesia. Measurement of the plasma concentrations (C_p) of the neuromuscular blocking agent (NMBA) and the concomitant intensities of paralysis allowed their simultaneous modelling. The pharmacokinetic parameters derived for pancuronium were in the range of previously reported values, except that the mean total systemic plasma clearance (0.79±0.28 ml·min^–1·kg^–1) was reduced and the mean terminal phase half-life (169 min) was longer in these patients. Plasma concentration and % paralysis data were successfully fitted to a previously proposed pharmacodynamic model. This model assumes a separate effect compartment which exchanges drug directly with the central kinetic compartment (integrated effect model). The steady-state C_p necessary to produce 50% paralysis (EC_pss(50)) was estimated to be 0.21±0.08 µg·ml^–1 (mechanical response) and 0.18±0.05 µg·ml^–1 (EMG response). An analysis using the Hill equation of the C_p-response relationship, during and after the constantrate infusion of pancuronium bromide, resulted in effective plasma concentrations for 50% paralysis (EC_p50) of 0.35±0.06 µg·ml^–1 and 0.20±0.09 µg·ml^–1, respectively, for mechanical twitch response. The corresponding values for EMG response were 0.32±0.06 µg·ml^–1 and 0.17±0.06 µg·ml^–1. Using this latter approach, the EC_p50 estimated during onset of paralysis was significantly higher than that estimated during offset of paralysis (p<0.05); no such difference was apparent between this latter parameter and the EC_pss(50) of the integrated effect model (p>0.05). No significant differences were observed between any of the pharmacodynamic parameter estimates generated from the data obtained from the two methods of assessment of neuromuscular function (mechanical vs. EMG response) (p>0.05).