Pharmacokinetics and bioequivalence study of the two 20-mg quinapril hydrochloride tablet formulations in healthy Thai male volunteers.

OBJECTIVE: To determine the pharmacokinetics and bioequivalence of two 20-mg quinapril hydrochloride tablet preparations; Quinaril (The Biolab Ltd, Bangkok, Thailand) as the test and Accupril as the reference. MATERIAL AND METHOD: The present study was a single dose, randomized two-period crossover design conducted in 24 healthy volunteers under fasting conditions with a 7-day washout period. Serial plasma concentrations of quinapril and its active metabolite quinaprilat up to 24 h after dosing were determined by HPLC with UV detection. The pharmacokinetic parameters were analyzed by noncompartmental analysis and the ANOVA was carried out using logarithmically transformed data of the AUC and C as well as untransformed T(max). RESULTS: There were no significant differences between the two preparations regarding the T(max) of quinapril and quinaprilat and their median T(max) were 0.5 h and 1.4 - 1.5 h, respectively. The half-life of quinapril (1.2 h) was faster than quinaprilat (1.8-1.9 h) although the volume of distribution (Vd/F) of quinapril (1.1 L/kg) was larger than quinaprilat (0.3 L/kg), however, its clearance rate (CL/F) was faster when compared to quinaprilat (20-26 ml/min/kg vs. 1.7 ml/min/kg). The mean (90% CI) for the ratios Reference/Test of quinapril were 0.99 (0.89-1.10), 0.99 (0.90-1.09) and 1.01 (0.90-1.14), respectively for AUC(0-24), AUC(0-infinity) and C(max). Similarly, the corresponding values for quinaprilat were 0.95 (0.90-1.01), 0.95 (0.90-1.01) and 1.03 (1.00-1.07), respectively. These values were within the bioequivalence range of 0.80 - 1.25, thus, demonstrated the bioequivalence of the two preparations. CONCLUSION: The results of the present study indicated that the two quinapril HCL preparations are bioequivalent and it can be assumed that they are therapeutically equivalent and exchangeable in clinical practice.

Efficacy and safety of gentamicin by interval and intravenous dosage adjustment based on the gestational age in Thai neonates.

OBJECTIVE: To determine the pharmacological efficacy and safety of the gentamicin regimen that adjusts intravenous dose and interval based on the gestational age (GA) in Thai neonates. MATERIAL AND METHOD: Neonates aged < or = 7 days, who had received gentamicin for clinically suspected or high risk of sepsis and had no contraindication to gentamicin usage were enrolled. They were stratified into four groups by GA as < or = 29, 30-33, 34-37 and > or = 38 weeks gestation. Gentamicin administration in each group was 5, 4.5, 4 and 4 mg/kg/dose every 48, 36, 36 and 24 hours respectively according to Neofax regimen. Peak serum gentamicin concentration (SGC), trough SGC and serum creatinine (Cr) were obtained. RESULTS: Forty-nine neonates were enrolled. Forty-four (89.7%) had peak SGC within the desirable range (5-12 mg/L). Three neonates had slightly high peak SGC. Their peak SGCs were 13.0, 12.21 and 12.20 mg/L. Two neonates had slightly low peak SGC. Their peak SGCs were 4.91 and 4.4 mg/L. All neonates had trough SGC below 2 mg/L. None had significant rising of serum Cr during the present study period. CONCLUSION: This gentamicin regimen yielded good pharmacological efficacy and safety in Thai neonates, who were in the first week of life and had no renal function impairment.

Effect of doses on the bioavailability of phenytoin from a prompt-release and an extended-release preparation: single dose study.

OBJECTIVE: To determine the effect of doses on the bioavailability of a prompt-release and an extended-release phenytoin capsule after given as single doses. MATERIAL AND METHOD: Eight healthy male volunteers were given single oral doses of 100, 200, and 300 mg of a prompt-release preparation (Ditoin) and an extended-release phenytoin (Dilantin Kapseals) preparation in a crossover design with a two weeks washout period after an overnight fast. Serial blood samples were collected over 72 h post-dose. Plasma phenytoin concentrations were determined by HPLC and pharmacokinetic parameters were analyzed by non-compartmental model. RESULTS: Rate of phenytoin absorption from the prompt-release preparation was more prolonged after the 300mg dose (T(max) 4.5 h) than those of the 100- and 200-mg doses (T(max) 3.5 and 3 h, respectively). Similarly, the T(max) of the 200- and the 300-mg extended-release preparation (5.5 and 4 h) were more prolonged than the 100-mg dose (3 h). Bioequivalence analysis showed that the C(max) of all doses of the prompt-release preparation were higher than those values of the extended-release preparation with the mean C(max) ratio (90% CI) of 1.32 (1.24-1.40), 1.26 (1.14-1.40), and 1.29 (1.10-1.51) for the 100-, 200- and 300-mg doses, respectively. The extent of absorption (AUC(0-infinity)) of 100-mg phenytoin was bioequivalent between the two preparations [mean AUC ratio (90% CI) of 1.15 (1.11-1.18)], however, for higher doses, the prompt-release products produced higher bioavailability than the extended-release products [mean AUC ratio (90% CI) of 1.19 (1.07-1.33) and 1.17 (0.98-1.38), respectively for the 200- and 300-mg doses]. The difference in the bioavailability did not affect the elimination of phenytoin and their half-lives were comparable (11-13 h). CONCLUSION: The bioavailability of phenytoin from both preparations increased proportionally over the dose range of 100-300-mg, however, the bioavailability of the prompt-release preparation was higher than the corresponding doses of the extended-release product.

Pharmacokinetic study of the combination of tacrolimus and fluconazole in renal transplant patients.

BACKGROUND: It was hypothesized that fluconazole in combination with tacrolimus can be used safely with an imitated area under curve (AUC) compared to tacrolimus. At every time point, this combination was presumed to correlate well with pre-intervention AUC, thus the dosage could be significantly reduced. MATERIAL AND METHOD: There were two groups of patients. Group I (n = 15) included patients who received tacrolimus at 0.1-0.3 mg/kg/day within one week after transplantation. These patients were studied for tacrolimus whole blood concentrations. The tacrolimus dosage was then reduced by 40% and given in combination with fluconazole at 100-200 mg/day for one week, tacrolimus whole blood concentrations were studied again. Group II (n = 8) included patients who had been transplanted for more than 3 months and had received a stable dosage of tacrolimus in combination with fluconazole for at least one month. RESULTS: In group I, before fluconazole combination, trough levels correlated well with AUC0-12. After fluconazole combination, trough levels still correlated well with AUC0-12. The after/before fluconazole-combination ratio of AUC0-12 and maximum tacrolimus concentration (Cmax) was 1.08 (90%CI; 0.98-1.19) and 1.17 (90%CI; 1.00-1.36), respectively. Correspondingly, the oral bioavailability, which was the after/ before fluconazole combination ratio of AUC0-12/dose and absorption rate (Cmax/dose/body weight), was significantly increased [2.08 (90%CI; 1.80-2.40) and 2.24 (90%CI; 1.99-2.51), respectively]. Tacrolimus clearance after the fluconazole combination was significantly reduced, compared with before the combination (14.74 vs 38.79 L/h, p = 0.001). Mean tacrolimus dosage in this group could be reduced from 10.7 mg/day before fluconazole combination to 5.7 mg/day after it and to 3.7 mg/day at 3 months after transplantation (p = 0.001). In group II, trough levels correlated well with AUC0-12 and the mean tacrolimus dosage in this group was only 2.9 mg/day. CONCLUSION: This present study showed a good correlation between tacrolimus trough levels and AUC, which occurred in monotherapy or in patients who received fluconazole. The tacrolimus trough levels could be trusted in monitoring patients who received a tacrolimus-based immunosuppressive regimen. The combination to fluconazole was ascertained and it was safe to reduce the dose of tacrolimus.

A bioequivalence study of the cefuroxime axetil in healthy volunteers.

The bioequivalence of 250-mg cefuroxime axetil was evaluated; Furoxime (by the Siam Bheasach Company, Thailand) as the test and Zinnat (GlaxoWellcome) as the reference. The two products were administered as a single dose according to a two-way crossover design, 1-week washout period to 12 healthy Thai male volunteers. Thereafter, serial blood samples were collected over a period of 15 hours. Plasma cefuroxime concentrations were measured by HPLC. The pharmacokinetic parameters were analyzed by noncompartmental analysis. Results: The Tmax [median (range, h)] of Furoxime and Zinnat were 1.5 (1.0-3.0) and 1.75 (1.0-3.5), respectively. The Tmax of Furoxime was faster than Zinnat with the mean (90% CI) of difference in Tmax of -0.5 [(-1.01)-0.01] h. Bioequivalence analysis showed that the AUC(0-infinity) and the Cmax of the two products were not significantly different. The point estimator (90% CI) for the ratio [Furoxime/Zinnat] of log transformed data of the AUC(0-infinity) and Cmax were 1.03 (0.98-1.20) and 1.09 (1.02-1.24), respectively and were within the bioequivalence range of 0.80-1.25.

Bioequivalence study of generic acyclovir compared with the brand name acyclovir.

The bioequivalence study of 200-mg generic acyclovir was conducted in healthy males. The reference Zovirax and the test Zevin were administered as a single oral dose after an overnight fast in a two-period, crossover design separated by 1 week. Serial blood samples were collected over a period of 24 hours. Plasma acyclovir concentrations were determined by HPLC and the pharmacokinetic parameters were analyzed by non-compartmental analysis. RESULTS: The t 1/2 for the test (4.5 +/- 2.4 h) and Zoviraxl (3.9 +/- 2.6 h) were comparable. The analysis of variance was carried out and the median Tmax (1.50 h) for the test was not statistically difference from Zovirax. The mean (90% CI) of the AUC0-infinity and the Cmax ratios for (Test/reference) were 0.95 (0.83-1.09) and 0.95 (0.83-1.10), respectively. These values fell within the bioequivalence criteria of 0.80-1.25, thus it was concluded that Zevin and Zovirax were bioequivalence.