Phenobarbital Abacavir

Clinically important, potentially hazardous interactions with abacavir, atorvastatin, bepridil, bupropion, carbamazepine, clarithromycin, cyclosporine, dexamethasone, digoxin, felodipine, fluticasone propionate, fosamprenavir, itraconazole, ketoconazole, lovastatin, methadone, midazolam, nicardipine, nifedipine, phenobarbital, phenytoin, rifabutin, simvastatin, sirolimus, St John s wort, systemic lidocaine, tacrolimus, tenofovir, trazodone, vinblastine, vincristine, voriconazole, warfarin, zidovudine... 

The UK manufacturer of abacavir says that phenobarbital and phenytoin may slightly decrease abacavir concentrations by affecting glucuronyl-transferases. There appears to be no other information on this. 

Valproate increases the bioavailability of zidovudine, and one case of severe anaemia was attributed to the interaction. A case of liver toxicity with combined use has also been reported. Phenytoin and phenobarbital are predicted to slightly decrease abacavir levels. 

The evidence indicates that the metabolism (glucuronidation) of zidovudine is inhibited by valproate so that its bioavailability is increased. It was suggested that this caused zidovudine haematological toxicity in the case reported. The glucuronidation of abacavir is predicted to be increased by drugs that can induce UDP-glucuronyltransferase, such as phenobarbital and phenytoin. ... 

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