The population pharmacokinetics of fluconazole have been investigated in 113 male subjects with HIV infection and AIDS. Plasma concentration-time data (between 1 and 17 observations per dose) were collected from individuals as part of a pharmacokinetic investigation (13 subjects) or during routine fluconazole therapy (100 subjects) for the treatment or prophylaxis of fungal infection. 2. A one-compartment pharmacokinetic model was used to describe the disposition of fluconazole after oral and intravenous infusion doses. Population pharmacokinetic parameters were generated using the NONMEM and P-PHARM computer programs. 3. The population estimates (calculated using NONMEM) of fluconazole clearance and volume of distribution were 0.78 l h-1 and 47.61, respectively. The intersubject variability for these parameters was 41% and 8%, respectively. The model-dependent estimate of the extent of absorption was 0.99 with an intersubject variability of 6%. Mean population estimates generated by NONMEM and P-PHARM were in close agreement. 4. Examination of the relationship between patient covariates and pharmacokinetic parameters indicated that intersubject variability in fluconazole clearance could in part be explained by the severity of disease (as indicated by CD4 + T-lymphocyte count) and renal function (indicated by estimated creatinine clearance). Other pharmacokinetic parameters were unaffected by these covariates. 5. Fluconazole clearance (estimated using NONMEM) in subjects with a CD4 + T-lymphocyte count less than and greater than 200 cells mm3 was 0.73 l h-1 (95% CI; 0.64-0.82 l h-1) and 0.99 l h-1 (95% CI; 0.86-1.12 l h-1), respectively. The regression model for fluconazole clearance that accounted for changes in renal function and disease severity was CL (l h-1) = 0.25 (33%) + 0.0057 (32%) x CLcr (in ml min-1) + 0.00068 (10%) x CD4 cell count (in cells mm-3) where intersubject variability (expressed as %CV) is shown in brackets. 6. Based on pharmacokinetic considerations a reduction in the dose of fluconazole would appear to be warranted in people with HIV infection who are seriously ill or who have compromised renal function. However, the emergence of resistance to fluconazole must also be considered when thinking of dosage adjustments.
