Phenytoin Atovaquone

Drugs that may affect zidovudine include acetaminophen, atovaquone, bone marrow suppressive/cytotoxic agents (eg, adriamycin, dapsone), clarithromycin, doxorubicin, fluconazole, ganciclovir, methadone, nelfinavir/ritonavir, phenytoin, probenecid, ribavirin, rifamycins, stavudine, trimethoprim, and valproic acid. 

An isolated report describes a 22-month-old girl treated with phenytoin, sodium valproate and topiramate for epilepsy and then with quinine sulfate (initially intravenously, then orally) followed by a single dose of sul-fadoxine/pyrimethamine for malaria. Her malaria film became negative after 4 days of the 7-day quinine course. About 1 month later she was found to have recrudescent falciparum malaria, which was treated with quinine sulfate and then atovaquone/proguanil. Although it is possible that quinine resistance may have occurred, the authors also considered that enzyme induction by phenytoin may have led to suboptimal quinine levels. Although quinine does not appear to affect phenytoin levels, the isolated case report suggests that levels of quinine may be reduced in the presence of phenytoin and it would seem prudent to monitor carefully concurrent use. 

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