Specific interaction studies have not been performed with efavirenz and abacavir. Clinically significant interactions would not be expected with abacavir since the NRTIs are metabolised via a different route than efavirenz and would be unlikely to compete for the same metabolic enzymes and elimination pathways. Abacavir had no effect on efavirenz pharmacokinetics when abacavir. efavirenz and indinavir were coadministered.