Pharmacokinetics of famciclovir, a prodrug of an antiherpes compound BRL39123, was studied following a single and repeat oral administration of famciclovir to healthy Japanese volunteers.
The active metabolite BRL39123 appeared in plasma at 0.5 hours after single ad ministration of famciclovir at 250, 500 and 1000 mg, reached C
max in 2 hours and decreased with T
1/2 of 1.84-2.03 hours. The C
max and AUC
0-∞ values of BRL39123 increased in proportion to the dose levels studied. The urinary excretions (% of dose) of BRL39123 and BRL42359 over 24 hours after administration were 53.35-60.92% and 5.06-6.40%, respectively, with no significant difference among the doses. Thus the pharmacokinetics of famciclovir after a single oral administration was linear in the dose range from 250 to 1000 mg.
When famciclovir 750 mg was administered once a day on Days 1 and 7, and three times a day at 5-hour intervals on Days 2 to 6, no significant difference was detected in either AUC
0-∞ or C
max between Days 1 and 7. During the repeated administration, the plasma concentration of BRL39123 immediately before the first administration of the next dosing day was near or below the limit of reliable determination, indicating no accumulation by the repeat administration. There was no significant difference in T
max or T
1/2 between Days 1 and 7. The urinary excretions of BRL39123 and total metabolites determined were statistically not different between Days 1 and 7, and also between Day 1 and through the administration period. Hence, there was no evidence for drug accumulation and for alternation of the pharmacokinetics of famciclovir by the repeat dose regimen studied.
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