Abstract

Coadministration of antitubercular and antiretroviral therapy is common in high-burden countries where tuberculosis is the commonest opportunistic infection. Concomitant use of rifampicin and many antiretroviral drugs is complicated by drug-drug interactions caused by the potent induction by rifampicin of genes involved in drug metabolism and transport, which could result in subtherapeutic antiretroviral drug concentrations. This review focuses on drug-drug interactions involving antiretrovirals used in resource-limited settings: the non-nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz or nevirapine, and ritonavir-boosted protease inhibitors. The reduction of nevirapine concentrations with concomitant rifampicin is greater than with efavirenz, particularly during the lead-in dose period when subtherapeutic concentrations occur in the majority of patients. There is reassuring data on the effectiveness of standard doses of efavirenz with concomitant rifampicin, but the largest cohort study found a higher risk of virological failure with nevirapine. The drug-drug interaction between rifampicin and ritonavir-boosted protease inhibitors is more marked than with the NNRTIs, and therapeutic concentrations have only been achieved with adjusted doses of lopinavir/ritonavir or with saquinavir/ritonavir (400/400 mg every 12 h). The major barrier to using adjusted dose protease inhibitors with rifampicin is the high rates of hepatotoxicity seen in healthy volunteers. The alternative strategy followed in resource-rich settings is to replace rifampicin with rifabutin, but even if the price of rifabutin were to be dramatically reduced it would be difficult to implement in high-burden countries where standardized antitubercular regimens with fixed-dose combinations are used.