Differential activation of human constitutive androstane receptor and its SV23 and SV24 splice variants by rilpivirine and etravirine.
Etravirine is metabolized by three cytochrome P450 enzymes that are in turn induced by rifampin. Consequently, co-administration of etravirine and rifampin is not recommended. To date, however, no clinical studies exploring the drug-drug interaction of this combination have been conducted. Here we report two cases of off-label etravirine use concurrently with antitubercular treatment, dictated by the unavailability of other treatments. Plasma drug concentrations were monitored by regular measurements. Our results appear to confirm the increased metabolism of etravirine through the induction of cytochrome P450 enzymes, but the adequacy of drug levels in all of the measurements and subsequent virological suppression suggest that this drug interaction may not be clinically relevant.