- Concomitant use with drugs that are highly dependent on cytochrome P450 for clearance, which, in the opinion of the investigators, may lead to the unexpected changes in their concentrations occurring after the addition of lopinavir/ritonavir or efavirenz. Examples include but are not limited to: wafarin-like anticoagulation , amiodarone, astemizole, cisapride, statin class of drugs, gemfibrozil, cyclosporine, ergonavine, ergotamine, methylergonavine, dihydroergotamine, dofetilide, flecanide, quinidine, fusidic acid, methadone, demerol, midazolam, triazolam, phenytoin, dilantin, pimozide, sirolimus, tacrolimus, propafenone, quinupristin, terfenadine, theophylline, rifampin, rifapentene, or rifabutin and illicit substances, including the recreational substance (ecstasy) methylenedioxymethamphetamine.