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.

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.