Altered Pharmacokinetics and Metabolism of Valproate after Replacement of Conventional Valproate with the Slow‐Release Formulation in Epileptic Patients

Abstract: Altered metabolism of valproate has been suggested as the mechanism of teratogenicity and hepatotoxicity of valproate. This study aimed at examining whether pharmacokinetics of a slow‐release formulation of valproate affects valproate metabolism. Thirty‐one epileptic patients were treated with fixed‐doses of conventional valproate for at least 2 months. Thereafter, the drug was replaced with the same doses of slow‐release formulation of valproate for 2 months. Blood samplings for determination of valproate and its metabolites by gas chromatography‐mass spectrometry were performed at three time‐points (just before morning dose and at 1 and 5 hr after morning dose) during both treatment phases. There was a significant difference (P<0.005) in the mean serum concentration (±S.D.) of valproate after 1 hr between conventional valproate (63.1±27.9 μg/ml) and slow‐release formulation of valproate (45.7±19.5 μg/ml). Mean serum concentrations (±S.D.) of 4‐en and hydroxy metabolites after 5 hr were significantly reduced after replacement with slow‐release formulation of valproate (4‐en: 29.5±14.0→23.0±15.3 ng/ml, 3‐OH: 488.5±234.0→419.6±171.1 ng/ml, 4‐OH: 404.3±124.7→342.8±147.6 ng/ml, 5‐OH: 102.8±54.4→81.0±43.6 ng/ml). The present study suggests that smaller diurnal fluctuations in valproate concentrations during treatment with slow‐release formulation of valproate result in decreased formations of minor metabolites including 4‐en, the most toxic metabolite.     

Pharmacokinetic characteristics of a new multiple unit sustained release formulation of sodium valproate

AIM: Two bioavailability studies were conducted in healthy male volunteers to determine the absorption characteristics of a new dosage form of sodium valproate consisting of sustained release pellets in a hard gelatine capsule. SUBJECTS, MATERIAL AND METHODS: To obtain first data on the in vivo behavior of the new multiple unit formulation a single dose pilot study in comparison with an oral solution was performed in 6 volunteers. Following the pilot study the pharmacokinetics were investigated versus a conventional enteric-coated tablet after multiple dosing in 18 volunteers. The volunteers were administered either a single or multiple dose of 300 mg sodium valproate. In both studies a wash-out period of at least 1 week elapsed between the periods. Valproic acid was determined from serum by gas chromatography at intervals suitable for obtaining concentration time curves for both regimens. RESULTS: The results of the pilot study showed that the valproate concentration in serum following administration of the new sustained release capsule increased smoothly and a longer lasting plateau was observed as compared with the solution. The average maximum serum valproate concentration of 12.5 microg/ml (sustained release capsule) and 24.3 microg/ml (solution) appeared at 9.3 h and 0.58 h after dosing. The extent of valproate absorption as reflected in the AUC data for each formulation was equivalent for the new sustained release capsule and reference formulation (AUC0-infinity: 369 +/- 88.9 and 339 +/- 76.2 microg/ml x h). Data obtained after multiple dose administration provided an indication of the consistency of valproate absorption from each dosage form. The time concentration profiles following twice daily administration of 300 mg sodium valproate in the multiple dose study showed that the extent parameters for absorption of valproate (AUC(8tau9tau) = 842 +/- 166 microg/ml x h) are equivalent with the enteric-coated preparation (AUC(8tau9tau) = 823 +/- 139 microg/ml x h). However, the fluctuation of the new sustained release formulation (PTF(8tau9tau) = 0.33 +/- 0.09) is about only one third of the fluctuation observed with the enteric-coated formulation (PTF(8tau9tau) = 0.88 +/- 0.22) when administered twice daily. CONCLUSION: These data indicate that the new sustained release capsule possesses desirable absorption characteristics in a form that allows twice daily or even once daily dosing and therefore improves patient compliance.     

Pharmacokinetic comparison of a slow-release clonidine with a conventional formulation after acute and chronic administration in hypertensives.

The pharmacokinetic characteristics of a slow-release formulation of clonidine (150 micrograms) were compared with those of a conventional formulation (75 micrograms) after acute and chronic (2 week) administration to 12 hypertensive subjects. The Tmax of the slow-release formulation was significantly later than for the conventional formulation after both acute (8.3 +/- 6 hr vs. 2.1 +/- 2 hr) and chronic administration (4.0 +/- 3 hr vs. 2.5 +/- 2 hr). Although the Tmax did not change significantly with acute and chronic administration of the conventional preparation, it was significantly shorter after chronic administration of the slow-release formulation when acute and chronic administration were compared. The Cmax was approximately 60% lower for the slow-release formulation (1 x 150 micrograms; 0.42 +/- 0.09 ng/mL) compared with the conventional formulation (2 x 75 micrograms; 0.70 +/- 0.12 ng/mL) after acute administration, whereas in the steady state, in which the dose of the conventional preparation was halved (75 micrograms), the Cmax values were comparable: 1 x 150 micrograms-0.99 +/- 0.27 ng/mL, 1 x 75 micrograms-0.84 +/- 0.20 ng/mL and the dose-normalized interdose AUC were identical for the conventional (16.2 +/- 4.3 ng/mL.hr) and slow release (16.6 +/- 5.3 ng/mL.hr) products. T1/2 values for the conventional formulation of clonidine exceeded 20 hours in all but one subject and were considerably longer than those in previous reports, including those of the authors, in which a less sensitive assay was used.(ABSTRACT TRUNCATED AT 250 WORDS)     

托吡酯与丙戊酸钠缓释片治疗难治性癫痫疗效比较

目的 :比较托吡酯与丙戊酸钠缓释片治疗难治性癫痫的疗效。方法 :托吡酯组 39例 ,丙戊酸钠组 4 1例 ,托吡酯成人及儿童剂量在约 2mo中逐渐增至 2 0 0mg·d- 1及 4mg·kg·d- 1左右 ,po ,bid。丙戊酸钠缓释片成人剂量 0 .5～ 1.0 g·d- 1,儿童剂量逐增至总量 15～ 30mg·kg·d- 1,为每日清晨或早晨、中午 2次服用。治疗 4mo及 6mo后评定疗效。结果 :托吡酯组治疗 6mo的继发性全身发作 ,简单及复杂性部分发作有效例数优于丙戊酸钠组 ,4例在加药期快时出现疲劳、嗜睡、注意力不集中等。丙戊酸钠组 1例发生骨髓造血功能严重低下。结论 :托吡酯治疗难治性癫痫简单及复杂部分性发作伴或不伴继发性全身发作疗效优于丙戊酸钠 ,无骨髓抑制 ,也无肝、肾功能损伤     

Study on the dose proportionality of the pharmacokinetics of sustained release sodium valproate

OBJECTIVE: A bioavailability study using three different doses was designed to assess the dose proportionality of a new multiple-unit sustained release formulation of sodium valproate. SUBIECTS AND METHODS: The study was performed using an open, three-period, randomized, crossover design. Twelve healthy male volunteers received on three occasions single oral doses of either 100 mg, 150 mg and 300 mg of a sustained release sodium valproate formulation. A wash-out period of at least 7 days elapsed between the administrations. Valproic acid was determined in serum by gas chromatography with flame-ionization detector. RESULTS: After administration of single doses of 100 mg, 150 mg and 300 mg sodium valproate the population mean curves reached their maxima of 4.3 microg/ml, 6.8 microg/ml and 12.8 microg/ml at 9 h, 9 h and 10 h, respectively. The geometric means of AUC0-tz and AUC0-infinity as well as Cmax related to each other approximately according to the expected ratios of 0.33:0.5:1. Point estimates and 90% confidence intervals for the ratios of geometric means of dose-normalized parameters (AUC0-tz, AUC0-infinity, Cmax) were included by the acceptance range of 80-125%. There were no differences in tmax as shown by the inclusion of zero in the 90% confidence interval for the median difference in tmax between the doses. CONCLUSION: Parameters determining the extent and rate of absorption (AUC and Cmax) increased proportionally with the dose of the new sustained release sodium valproate formulation. This pharmacokinetic behavior offers easier treatment management as dose adjustment is facilitated.     

Circadian changes in pharmacokinetics of sulfamethoxazole administered orally to rabbits

Circadian variations of sulfamethoxazole pharmacokinetics were studied after a single oral administration of sulfamethoxazole, 50 mg/kg, to rabbits at 09:00 (a.m.) and 22:00 (p.m.). The profiles of plasma sulfamethoxazole concentration showed from 6 h to 24 h significant statistical difference (p<0.05) between 09:00 and 22:00. The half-life (t(1/2)) was significantly shorter in the morning (11.2 +/- 3.2 h) when compared to the nighttime (15.4 +/- 3.5 h) (p< 0.05). The AUC was significantly decreased in the morning (1325 +/- 264 microg/ml x h) than that in the nighttime (2059 +/- 379 microg/ml x h) (p<0.05). Total body clearance (CLt) was significantly higher when sulfamethoxazole was given in the morning (6.65 +/- 0.23 ml/min) versus in the nighttime (4.28 +/- 0.20 ml/min) (p<0.05).     

Retrospective analysis of serum valproate levels and need for an antidepressant drug.

We sought to determine whether patients receiving valproate plus an antidepressant had significantly lower serum valproate levels before initiation of the antidepressant than those patients receiving valproate without an antidepressant. We further sought to identify the prevalence of antidepressant-induced mania and to determine if valproate provided a protective effect against antidepressant-induced mania. A computer database search from January 1, 1990-June 30, 1998, identified patients with bipolar or schizoaffective disorder treated with valproate. Patients receiving an antidepressant during valproate therapy were identified as the treatment group (9 patients), and the remaining patients served as the control group (17 patients). Serum valproate levels were recorded just before starting the antidepressant for the treatment group and monthly during a comparable period for the control group. The mean time to antidepressant initiation was 15 +/- 8 weeks. The mean serum valproate level just before antidepressant initiation was significantly lower for the treatment group compared with the mean serum valproate level averaged over 16 +/- 6 weeks for the control group (54 +/- 24 vs 73 +/- 13 microg/ml, p<0.05). Four patients (44%) developed antidepressant-induced mania. Three required discontinuation of the antidepressant; their serum valproate levels were 54, 60, and 71 microg/ml. Patients requiring the addition of an antidepressant had significantly lower valproate serum levels than those who did not require an antidepressant. Further study is necessary to determine whether higher serum valproate levels are needed for prevention of depressive symptoms in bipolar and schizoaffective disorders.     

Effect of sodium/potassium salt (potash) on the bioavailability of ibuprofen in healthy human volunteers.

The influence of sodium/potassium salt water extract incorporated in a traditional meal on the bioavailability of Ibuprofen tablets 400mg dose was studied in 6 healthy human volunteers. There was a statistically significant decrease in the plasma levels of ibuprofen, and its metabolites, hydroxy-ibuprofen and carboxy-ibuprofen, respectively, when the meal containing sodium/potassium salt extract was administered with the ibuprofen tablets than when taken under fasting state or with the meal without the fruit extract. The Cmax, AUC0-6hr and Ka for ibuprofen decreased from 38.04 +/- 0.70microg/ml to 20.06 +/- 1.21microg/ml (p<0.05); 28.030 +/- 2.40microg/ml.hr to 14.180 +/- 1.12microg/ml.hr (p<0.05) and 1.048 +/- 0.02hr(-1) to 0.602 +/- 0.03hr(-1). Similarly, the Cmax for hydroxy-ibuprofen and carboxy-ibuprofen decreases from 43.04 +/- 0.76microg/ml to 27.21 +/- 0.24microg/ml (p<0.05) and 48 +/- 0.71microg/ml to 31.08 +/- 0.12microg/ml (p<0.05) respectively; while AUC0-6hr for hydroxy-ibuprofen decreased from 34.120 +/- 0.49microg/ml.hr to 16.410 +/- 0.27microg/ml.hr while that of carboxy-ibuprofen decreased from 36.121 +/- 1.97microg/ml.hr to 19.278 +/- 0.92microg/ml.hr respectively. The Kel for hydroxy-ibuprofen increased from 0.71 +/- 0.94 hr(-1) to 0.81 +/- 0.21 hr(-1) (p<0.05) respectively. The study has indicated that sodium/potassium salt extract significantly decreased the bioavailability of ibuprofen.     

Effect of Tamarindus indica. L on the bioavailability of ibuprofen in healthy human volunteers.

The influence of Tamarindus indica L fruit extract incorporated in a traditional meal on the bioavailability of Ibuprofen tablets 400 mg dose when given concurrently was studied in 6 healthy human volunteers. There was a statistically significant increase in the plasma levels of Ibuprofen and its metabolites hydroxy-ibuprofen and carboxy-ibuprofen respectively, when the meal containing Tamarindus indica fruit extract was administered with the ibuprofen tablets than when taken under fasting state or with the meal without the fruit extract. The C(max), AUC(0-6 hr) and Ka for ibuprofen increased from 38 +/- 0.70 microg/ml to 42 +/- 0.98 microg/ml (p > 0.05); and 28.03 +/- 2.40 microg/ml x hr to 56.51 +/- 0.16 microg/ml x hr (p < 0.05) and 1.048 +/- 0.02hr(-1) to 2.781 +/- 0.11 hr(-1) (p < 0.05) respectively. There was no change in the t(max) (120.00 +/- 0.43m) but there was a decrease in the k(el) from 0.63 +/- 0.20 hr(-1) to 0.46 +/- 0.11 hr(-1) (p<0.05). Similarly the C(max), AUC(0-6 h) and Ka for hydroxy-ibuprofen rose from 43 +/- 0.76 microg/ml to 45 +/- 0.16 microg/ml (p < 0.05); 39.04 +/- 2.30 microg/ml x hr to 59.49 +/- 2.39 microg/ml.hr in (p < 0.05) and 1.498 +/- 0.79hr(-1) to 3.442 +/- 0.23 hr(-1) (p < 0.05) respectively; while the C(max), AUC(0-6 h) and Ka for carboxy-ibuprofen rose from 48 +/- 0.7 microg/ml to 51 +/- 0.16 microg/ml (p < 0.05); 41.972 +/- 0.68 microg/ml x hr to 63.948 +/- 0.12 microg/ml x hr (p < 0.05) and 1.649 +/- 0.08 hr(-1) to 4.187 +/- 0.42 hr(-1) (p < 0.05) respectively. The study has indicated that Tamarindus indica L. fruit extract significantly increased the bioavailability of Ibuprofen.     

Effect of valproate on free plasma phenytoin concentrations.

The plasma protein binding of phenytoin was studied in nine epileptic patients before and during addition of sodium valproate to the drug therapy. The free phenytoin fraction in plasma was significantly greater during sodium valproate treatment. The mean free fraction rose from 0.135 +/- 0.019 (s.d.) to 0.182 +/- 0.030. Total plasma phenytoin concentration fell significantly from a range of 4.3-26.2 micrograms/ml to 3.4-19.8 micrograms/ml during sodium valproate treatment. Neither the free plasma concentration nor the saliva concentration of phenytoin was significantly altered by sodium valproate. No significant correlation was found between plasma valproic acid concentrations and the change in phenytoin binding. We conclude that valproic acid displaces phenytoin from plasma protein binding sites but does not inhibit its metabolism.     

Bioequivalence of two oral formulations of nizatidine capsules in healthy male volunteers

PURPOSE: The purpose of this randomized, crossover study was to compare the bioavailability of a generic and an innovator formulation of nizatidine 300 mg capsules under fasting conditions. METHODS: Twenty blood samples per period were collected from 20 healthy, Arab male volunteers over 16 h, plasma nizatidine concentrations were determined by HPLC assay, and pharmacokinetic parameters were determined by the non-compartmental method. RESULTS: Mean+/-SD C(max), T(max), AUC(0-->t), AUC(0-->infinity), and t1/2 were 2.96+/-0.54 and 3.28+/-0.68 microg/ml, 1.31+/-0.70 and 0.93+/-0.38 h, 9.04+/-1.66 and 9.03+/-1.94 microg x h/ml, 9.17+/-1.64 and 9.12+/-1.94 microg x h/ml, and 1.64+/-0.21 and 1.58+/-0.22 h for the generic and innovator formulation, respectively. The parametric 90% confidence intervals on the mean of the difference between log-transformed values were 98.06% to 103.21%, 98.74% to 103.71%, and 83.37% to 101.34%, for AUC(0-->t), AUC(0-->infinity), and C(max), respectively. CONCLUSION: The results indicate that these two formulations are equivalent in the rate and extent of absorption.     

Bioequivalence of a new sustained-release formulation of sodium valproate, valproate modified-release granules, compared with existing sustained-release formulations after once- or twice-daily administration

STUDY OBJECTIVE: To compare the pharmacokinetic properties of valproate modified-release (MR) granules with those of two existing valproate sustained-release (SR) formulations to confirm their bioequivalence. DESIGN: Two randomized, open-label, two-period crossover studies under fasting conditions, and one open-label, randomized, single-dose, three-period crossover study under fasting and nonfasting conditions. Each study had a 7-day washout interval between periods. SETTING: Three hospitals in France. SUBJECTS: Healthy male Caucasian volunteers aged 18-35 years (27 subjects in study 1, 24 in study 2, and 24 in study 3). INTERVENTION: In studies 1 and 2, during two 15-day periods, subjects received either valproate MR granules or an existing valproate SR formulation. In study 3, subjects received only valproate MR granules 500 mg, once with water after a 10-hour fast, once with yogurt after a 10-hour fast, and once 30 minutes after a high-fat morning meal. MEASUREMENTS AND MAIN RESULTS: Blood samples were collected, and pharmacokinetic parameters of valproic acid were determined for single-dose (studies 1-3) and repeated-dose (studies 1 and 2) administration. The 90% confidence intervals (CIs) for area under the concentration-time curve and maximum concentration (C max ) were in the acceptance limits for bioequivalence (i.e., 90% CI 0.80-1.25) after single and repeated doses of valproate MR granules administered once/day or twice/day. Although time to C max was slightly decreased with valproate MR granules, this difference did not induce a significant difference in terms of C max . Valproate MR granule formulation was bioequivalent with existing SR formulations. High-fat breakfast or yogurt did not modify either the bioavailability or pharmacokinetic profile of valproate MR granules. This formulation was well tolerated. The adverse event profile did not differ among the various regimens. CONCLUSION: Valproate MR granules, administered once/day or twice/day, may be an attractive alternative to existing SR formulations for patients who have difficulties with swallowing tablets or who favor granules over tablets.     

In vivo bioequivalence study of Sulpirid (GYKI-Alkaloida) and Dogmatil fort (Delagrange) 200 mg sulpiride tablets in healthy volunteers]

A single-dose, "crossover" bioequivalence study was conducted in healthy volunteers by comparing sulpiride serum levels after oral administration of the Test Product Sulpiride (200 mg) (GYKI-Alkaloida) in fasting subjects with those produced after oral administration of a marketed reference product (200 mg) (Delagrange Co., France). Statistical comparisons of Cmax, Tmax and AUC0-infinity have been performed utilizing ANOVA with subject, group, subject within group, period and product as sources of variance. No significant differences between the Test Drug and the Reference Drug considering the pharmacokinetic parameters Cmax, Tmax and AUC0-infinity were found. The 95% confidence intervals were as follows: AUC0-infinity: -20.46% and 31.19%, Cmax: -28.05% and 26.65% and Tmax: -43.53% and 20.67%. In the study for the analysis of Sulpiride a specific HPLC procedure with uv detection (lambda = 228 nm) and an internal standard were applied according to P. Nicolas et al. with modification. Sulpiride levels in serum reached a maximum at 4.4 hr +/- 1.5 (S.D.) following administration of Sulpiride tablet and at 5.0 hr +/- 0.8 (S.D.) after Dogmatil fort tablet. The maximal serum concentrations were 506.1 ng/ml +/- 87.2 (S.D.) and 509.1 ng/ml +/- 101.9 (S.D.) for Sulpiride and Dogmatil fort, respectively. The half-life of Sulpiride in serum was 9.9 hr +/- 1.3 (S.D.) following dosing with Dogmatil fort tablet and 12.2 hr +/- 3.0 (S.D.) following dosing with Sulpiride tablet.     

A study of the safety, efficacy, and tolerability of switching from the standard delayed release preparation of divalproex sodium to the extended release formulation in patients with schizophrenia

OBJECTIVE: To assess the safety, efficacy, and tolerability of switching from a multiple dose preparation of divalproex sodium delayed release (DR) to once-daily dosing with divalproex sodium extended release (ER) in patients with schizophrenia already receiving the standard DR formulation. METHOD: Thirty subjects with schizophrenia were switched from divalproex DR to a 4-week open-label treatment trial of the ER formulation. Baseline plasma levels of valproate were obtained 12 hours postdose. Patients were converted from divalproex DR to ER on a 1.0:1.0 mg basis (rounded up to the nearest 500-mg increment) if baseline valproate plasma levels were > or =85 microg/mL; otherwise, the conversion rate was 1.0:1.2 mg rounded up. Measured at baseline and end point were the Brief Psychiatric Rating Scale and the Udvalg for Kliniske Undersogelser Side Effect Rating Scale. End point plasma levels were obtained at both 12 and 24 hours postdose. RESULTS: Patients who switched from divalproex DR to ER had a small (and probably clinically insignificant) improvement noted on the total Brief Psychiatric Rating Scale at end point (mean change +/- SD = -2.3 +/- 5.4; t = -2.2538; df = 28; P = 0.0322) and on the Udvalg for Kliniske Undersogelser (mean change+/- SD = -2.2+/- 4.1; t = -2.7361; df = 26; P = 0.0111). Baseline and end point trough plasma levels were 80.1 +/- 20.4 and 73.1 +/- 24.2 microg/mL, respectively. Patients who converted on a 1.0:1.0 mg basis had lower end point valproate trough plasma levels than at baseline but did not experience deterioration on their psychopathology. For all patients, end point valproate peak and trough plasma levels were statistically significantly different (t = -3.8706; df = 27; P = 0.0006), but these differences were small in magnitude (mean +/- SD = 14.6 +/-19.6 microg/mL). Seven patients experienced spontaneously reported adverse events, but none required early termination from the protocol. CONCLUSIONS: Switching to a once-daily formulation of ER divalproex can be accomplished without a deterioration in psychopathology. The ER formulation of divalproex sodium appears well tolerated. A parallel group design will be necessary to confirm these findings.     

Pharmacokinetics of quinidine and three of its metabolites in man

Disposition parameters of quinidine and three of its metabolism, 3-hydroxy quinidine, quinidine N-oxide, and quinidine 10,11-dihydrodiol, were determined in five normal healthy volunteers after prolonged intravenous infusion and multiple oral doses. The plasma concentrations of individual metabolites after 7 hr of constant quinidine infusion at a plasma quinidine level of 2.9 +/- (SD) 0.3 mg/L were: 3-hydroxy quinidine, 0.32 +/- 0.06 mg/L; quinidine N-oxide, 0.28 +/- 0.03 mg/L; and quinidine 10,11-dihydrodiol, 0.13 +/- 0.04 mg/L. Plasma trough levels after 12 oral doses of quinidine sulfate every 4 hr averaged: quinidine, 2.89 +/- 0.50 mg/L; 3-hydroxy quinidine, 0.83 +/- 0.36 mg/L; quinidine N-oxide, 0.40 +/- 0.13 mg/L; and quinidine 10,11-dihydrodiol, 0.38 +/- 0.08 mg/L. Relatively higher plasma concentrations of 3-hydroxy quinidine metabolite after oral dosing probably reflect first-pass formation of this quinidine metabolite. A two-compartment model for quinidine and a one-compartment model for each of the metabolites described the plasma concentration-time curves for both i.v. infusion and multiple oral doses. Mean (+/- SD) disposition parameters for quinidine from individual fits, after i.v. infusion were as follows: Vl, 0.37 +/- 0.09 L/kg; lambda 1, 0.094 +/- 0.009 min-1; lambda 2, 0.0015 +/- 0.0002 min-1; EX2, 0.013 +/- 0.002 min-1; clearance (ClQ), 3.86 +/- 0.83 ml/min/kg. Both plasma and urinary data were used to determine metabolic disposition parameters. Mean (+/- SD) values for the metabolites after i.v. quinidine infusion were as follows: 3-hydroxy quinidine: formation rate constant kmf, 0.0012 +/- 0.0005 min-1, volume of distribution, Vm, 0.99 +/- 0.47 L/kg; and elimination rate constant, kmu 0.0030 +/- 0.0002 min-1. Quinidine N-oxide: kmf, 0.00012 +/- 0.00003 min-1; Vm, 0.068 +/- 0.020 L/kg; and kmu, 0.0063 +/- 0.0008 min-1. Quinidine 10,11-dihydrodiol: kmf, 0.0003 +/- 0.0001 min-1; Vm, 0.43 +/- 0.29 L/kg; and kmu, 0.0059 +/- 0.0010 min-1. Oral absorption of quinidine was described by a zero order process with a bioavailability of 0.78. Concentration dependent renal elimination of 3-hydroxy quinidine was observed in two out of five subjects studied.     

Concentration-effect relationship of levodopa in patients with Parkinson's disease after oral administration of an immediate release and a controlled release formulation.

1. The relationship between plasma concentration of levodopa and motor-response was investigated in 12 patients with Parkinson's disease who showed marked response fluctuations, after a single oral dose of an immediate release (IR) formulation (100 mg levodopa/25 mg genserazide) and a controlled release (CR) formulation (300 mg levodopa/75 mg benserazide), using a double-blind, randomized, cross-over design. 2. The sum score of the Columbia University Rating Scale (CURS sigma) was used for pharmacodynamic assessment. A sigmoidal Emax-model was fitted to the data using a semiparametric pharmacokinetic/dynamic approach. 3. The dose-corrected AUC of levodopa after the IR-formulation was 27.5 (+/- 9.1 s.d.) ng ml-1 h per mg and 23.2 (+/- 4.6 s.d.) ng ml-1 h per mg after the CR-formulation. Cmax was 1714 (+/- 1027 s.d.) ng ml-1 after the IR-formulation and 1494 (+/- 383 s.d.) ng ml-1 after the CR-formulation. 4. With both preparations, the maximal response to levodopa (Emax) was a decrease in the CURS sigma rating of about 27 scores. Estimates of the EC50 of levodopa were 495 (+/- 144 s.d.) ng ml-1 (IR) and 1024 (+/- 502 s.d.) ng ml-1 (CR), respectively (95%-CI: 1.51-2.66, point estimator 1.95). The mean duration of the motor response was 1.9 (+/- 0.5 s.d.) h (IR) and 2.8 (+/- 0.7 s.d.) h (CR), respectively (95%-CI: 1.12-2.04, point estimator 1.53).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of a new extended-release nifedipine formulation following a single oral dose, in human volunteers

This study aimed to define the pharmacokinetics of nifedipine following oral administration of a new extended-release formulation. Twelve healthy volunteers of both sexes, aged 39 +/- 4 years, were treated with a single oral tablet of a new extended-release formulation containing 40 mg of nifedipine. Samples of venous blood were taken before dosing, after 30 min and at 1, 2, 4, 8, 12, 16, 20 and 24 h after administration. Nifedipine concentration was measured by means of a high-performance liquid chromatography method. Noncompartmental pharmacokinetics parameters were then calculated. The plasma concentration of nifedipine increased slowly and in seven subjects biphasic peaks occurred. The mean values were as follows: t(max): 8.5 +/- 1.2 h; C(max): 36.55 +/- 6.76 ng/ml; AUC: 347.06 +/- 51.61 ng/h/ml; AUC 409.99 +/- 61.08 ng/h/ml; A(half-life): 2.26 +/- 0.36 h; D(half-life): 2.43 +/- 0.44 h; E(half-life): 4.62 +/- 0.79 h. Twenty-four hours after administration nifedipine was still detectable (3.17 +/- 0.67 ng/ml). Arterial blood pressure decreased and heart rate increased concurrently and proportionally to the increase in nifedipine concentration. Extended-release nifedipine formulations have better tolerability profiles than immediate-release formulations, which are at present not recommended in the treatment of hypertension, hypertensive crises or myocardial infarction. This new extended-release formulation has interesting pharmacokinetic parameters and may be effective in conditions in which dihydropyridine calcium channel blockers are indicated.     

Platelet CD62 expression and PDGFAB secretion in patients undergoing PTCA and treatment with abciximab

AIMS: To investigate a correlation of the platelet activation marker CD62 and secretion of the growth factor PDGF from platelets in coronary patients under therapy with the GPIIb/IIIa-inhibitor abciximab. METHODS: Flow cytometric assessment of fibrinogen binding (GPIIb/IIIa-binding site) and CD62 expression, as well as PDGF release of human platelets (immunoassay) and platelet aggregation with 20 microM ADP and 2 microg ml(-1) collagen were evaluated in nine patients with stable coronary artery disease. Patients were undergoing elective balloon angioplasty and were treated with aspirin (100 mg day(-1)), heparin (ACT < 220 s) and abciximab (bolus and infusion over 12 h). Blood samples were obtained before initiation of abciximab therapy (under aspirin and heparin) (I), 3 h after angioplasty under abciximab (II) and 12 h after termination of abciximab infusion (III). RESULTS: Compared with sample I before abciximab therapy, fibrinogen binding was reduced to 37% (+/- 34 s.d., P < 0.05) (II) and 55% (+/- 40 s.d., P < 0.05) (III). Reduced fibrinogen binding also led to a significant reduction of the aggregation response to ADP (down to 37% +/- 20) and collagen (down to 0%). Mean fluorescence intensity of CD62-expression was 78 units (+/- 20 s.d.) (I), 72 units (+/- 14 s.d.) (II) and 64 units (+/- 12 s.d., P < 0.05) (III). PDGF release from isolated, washed platelets was 99 (+/- 33 s.d.) ng/10(9) platelets at (I), 82 (+/- 31 s.d.) ng/10(9) platelets and 96 (+/- 30 s.d.) ng/10(9) platelets. CONCLUSIONS: The results indicate that despite a strong reduction of GPIIb/IIIa-binding and platelet aggregation, CD62 as a marker of platelet secretion and the secretion product PDGF were only slightly reduced under abciximab treatment. No direct correlation between CD62 expression and PDGF release could be demonstrated.     

Ranitidine: single dose pharmacokinetics and absolute bioavailability in man

1 Ranitidine single dose pharmacokinetics and absolute bioavailability have been studied in five healthy male volunteers. Following an overnight fast, 150 mg was given intravenously as a bolus injection or orally as a tablet formulation to each subject on separate occasions. 2 Following intravenous administration, plasma levels declined biexponentially. The mean (+/- s.d.) distribution half-life (t 1/2 alpha) was 6.6 +/- 1.6 min; plasma half-life (t 1/2 beta) was 1.7 +/- 0.2 h; the volume of distribution (V) was 96 +/- 9 1; total body clearance (CL) was 647 +/- 94 ml/min and renal clearance (CLR) 520 +/- 123 ml/min. 3 Following oral administration plasma levels showed a bimodal pattern with a first peak at 1.1 +/- 0.4 h and a second peak at 3 +/- 0 h. The absolute availability was 60 +/- 17%. The plasma half-life (t 1/2) of 2.3 +/- 0.4 h was significantly longer (P less than 0.05) after oral than after i.v. administration. 4 Renal excretion of unchanged ranitidine accounted for 79 +/- 9% of the dose after i.v. administration and for 27 +/- 7% after oral administration. 5 Our results suggest a more extensive biotransformation of ranitidine and biliary excretion of metabolites after oral administration while i.v. administration ranitidine is preferentially excreted unchanged in the urine.