PHARMACOKINETICS OF DIDANOSINE AND KETOCONAZOLE AFTER COADMINISTRATION TO PATIENTS SEROPOSITIVE FOR THE HUMAN-IMMUNODEFICIENCY-VIRUS

The steady-state pharmacokinetics of didanosine (DDI) and ketoconazole (KET) were evaluated when the agents were administered alone or concurrently to patients seropositive for the human immunodeficiency virus. Using a randomized, three-way crossover design, multiple oral doses of DDI (375 mg twice daily for 4 days), KET (200 mg daily for 4 days) or the combination were administered under fasting conditions. When DDI and KET were coadministered, KET was given 2 hours before the morning dose of didanosine. Serial blood samples and total urine output were a collected after the administration of a final single dose on day 5 of each treatment session. Samples were analyzed using high-pressure liquid chromatography (HPLC)/ultraviolet (UV) or fluorescence methods specific for unchanged DDI (plasma and urine) or KET (plasma only). Pharmacokinetic parameters were calculated using noncompartmental methods. The average DDI maximum peak plasma concentration (Cmax) value at steady state was significantly less when DDI was administered with KET (1836 ng/mL) than when DDI was administered alone (2094 ng/mL), although the magnitude of the decrease was only 12%. Didanosine area under the curve (AUC(0 - tau)) for the combination (2872 hr.ng/mL) was 8% less than when DDI was given alone (3107 hr.ng/mL); the difference was not significant. There were no significant differences among the other evaluated parameters (time to reach peak concentration [tmax], half-life [t1/2], renal clearance [CL(R)], or urinary recovery [UR]) between the two DDI treatments. There were no significant differences among any of the pharmacokinetic parameters between the two KET treatments. It is concluded that the pharmacokinetics of DDI and KET are not affected to a clinically significant degree by coadministration of multiple oral doses of the two agents under the current study conditions. It is not necessary to alter the dosing regimen of either drug so long as KET is administered 2 hours before DDI.