[Indinavir-ritonavir combination: pharmacologic results and tolerance in patients infected by HIV]

Ritonavir (RTV) is a powerful inhibitor of P450 3A4 cytochorme. When given in combination with indinavir (IDV) it increases the IDV trough concentrations (Cmin) allowing a lower IDV dosage in a twice a day regimen, independently of meals. We report tolerance data and IDV Cmin levels observed in plasma and cerebrospinal fluid (CSF) in a cohort of HIV-infected patients treated with the IDV-RTV combination at different dosages of IDV and RTV.

IDV Cmin was assayed 56 times in 40 patients (few patients had received different dosages of the IDV-RTV combination). Tolerance was recorded.

For patients given the IDV-RTV combination at the doses of 800/100 mg b.i.d., 800/200 mg b.i.d. or 400/400 mg b.i.d., the IDV Cmin was 12 times the median IDV IC95. If the Cmin/IC95 ratio was greater than 10 with the 800/100 mg b.i.d. regimen and virological success was achieved, the IDV dosage was reduced to 400 mg b.i.d. For these patients, the 400/100 mg b.i.d. IDV-RTV regimen always gave a Cmin above the IDV IC95. Median Cmin for IDV in CSF was 146 ng/ml (range 71-881 ng/ml), above the IDV IC95. It was possible to control most of the adverse effects by reducing dosage after obtaining the IDV pharmacological levels. Definitive interruption of treatment was required in only 2 cases at mean follow-up of 7.9 months.

The IDV-RTV combination should be used to improve observance of antiretroviral treatments and reduce the risk of virological failure related to low plasma levels. The IDV-RTV combination at 800/100 mg b.i.d. is a useful protocol when IDV efficacy alone is the goal. The 400/400 mg b.i.d. IDV-RTV regimen is an interesting alternative when efficacy of both inhibitors is the goal. Drug assays should be systematic to adapt individual dosages and limit the risk of adverse effects.