Effect of fluconazole on pharmacokinetics of 2',3'-dideoxyinosine in persons seropositive for human immunodeficiency virus.

Fluconazole inhibits cytochrome P-450-mediated enzymatic metabolism of several drugs. Since hepatic metabolism is partially responsible for 2',3'-dideoxyinosine (didanosine or ddI) elimination, fluconazole therapy may lead to increased ddI concentrations in serum and subsequent concentration-dependent adverse effects. The purpose of this study was to determine if ddI pharmacokinetics are influenced by a 7-day course of oral fluconazole. Twelve adults with human immunodeficiency virus (HIV) who had received a constant dosage of ddI for at least 2 weeks were investigated. On study day 1, multiple serum samples for determination of ddI concentrations were obtained over 12 h. Then subjects received a 7-day course of oral fluconazole (200 mg every 12 h for two doses and then 200 mg once daily for 6 days) while ddI therapy continued. Following the last dose of fluconazole, serum samples for determination of ddI concentrations were again obtained over 12 h. ddI concentrations in serum were analyzed by radioimmunoassay. In contrast to previously published data, there was marked between-subject variability in ddI areas under the concentration-time curve, even when the dose was normalized for weight. No significant differences were found between mean ddI areas under the concentration-time curve from 0 to 12 h on study day 1 (1,528 +/- 902 ngx.hr/ml) and following fluconazole treatment (1,486 +/- 649 ngx.hr/ml) . There were no significant differences in other pharmacokinetic parameters, such as ddI peak concentrations in serum (971 +/- 509 and 942 +/- 442 ng/ml) or half-lives (80 +/- 32 and 85 +/- 21 min.) before and after fluconazole treatment, respectively. We conclude that a 7-day course of oral fluconazole does not significantly alter ddI pharmacokinetics in adults that are infected with human immunodeficiency virus.