The interaction of saquinavir (soft gelatin capsule) with ketoconazole, erythromycin and rifampicin:: comparison of the effect in healthy volunteers and in HIV-infected patients

Objective: The aim of this study was to compare the effect of ketoconazole, erythromycin and rifampicin on the pharmacokinetics of saquinavir soft-gelatin formulation (Fortovase; FTV) in healthy volunteers with that in HIV-infected patients at steady state after administration of 1200 mg three times daily. Methods: In two open-labelled, randomised, crossover studies pharmacokinetic parameters were calculated in healthy volunteers who received on one occasion multiple doses of 1200 mg FTV three times daily alone and on the other occasion in combination with multiple doses of either 400 mg ketoconazole once daily or 600 mg rifampicin once daily. In another open-labelled, multicentre study, 33 HIV-infected patients underwent a pharmacokinetic assessment after 36-51 weeks of treatment with FTV and were then given additionally multiple doses of either 200 mg ketoconazole once daily, 250 mg erythromycin four times daily or 600 mg rifampicin once daily. Pharmacokinetic parameters of saquinavir were determined again at the end of the combination treatment. Results: In healthy volunteers, coadministration of ketoconazole increased saquinavir area under the curve from time 0 to 8 h (AUC(0-8h)) by 190% (95% CI: 90-343) whereas coadministration with rifampicin resulted in a decrease for AUC(0-8h) by 70% (95% CI: 50-82). In HIV-infected patients, coadministration of ketoconazole and erythromycin increased AUC(0-8h) of saquinavir by 69% (95% CI: 14-150) and 99% (95% CI: 33-198), respectively. When saquinavir was given together with rifampicin, exposure of saquinavir in terms of AUC(0-8h) was decreased by 46% (95% CI: 18-65) compared with the baseline assessment. Conclusion: Interactions of saquinavir with ketoconazole, erythromycin and rifampicin were observed in healthy volunteers as well as patients. The effects observed in patients, however, appear to be less pronounced. The enzyme induction caused by rifampicin might lead to subtherapeutic levels of saquinavir and this finding appears to be of clinical relevance.