Abacavir has also been shown in vitro not to inhibit CYP 3A4, CYP2C9 or CYP2D6 enzymes at clinically relevant concentrations. Induction of hepatic metabolism has not been observed in clinical studies. Therefore, there is little potential for interactions with antiretroviral PIs.

Coadministration has not been studied. Based on the different elimination pathways of abacavir for which metabolism is not mediated by CYP450, no interactions are expected for this medicinal compound and boosted darunavir. Boosted darunavir can be used with this NRTI without dose adjustment.

No dosage adjustments are recommended when darunavir/ritonavir is co-administered with abacavir.

The steady-state pharmacokinetics of abacavir (600 mg once daily, plus two NRTIs – excluding tenofovir) were investigated when coadministered with darunavir/ritonavir (900/100 mg once daily) to 19 HIV+ subjects in a cross-over study. Abacavir AUC, Cmax and Cmin decreased by 27%, 22% and 38%, respectively in the presence of darunavir/ritonavir. Exposure of abacavir’s active intracellular carbovir triphosphate anabolite was decreased, however, the clinical significance of this decrease is unclear.