Drug Interactions between bosentan and Viramune XR

MONITOR: Coadministration with bosentan may decrease the plasma concentration and antiviral effects of nevirapine. The proposed mechanism is increased clearance due to bosentan-mediated induction of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of nevirapine. In addition, concomitant use of bosentan with other hepatotoxic agents, such as nevirapine, may potentiate the risk of liver injury.

MANAGEMENT: Given the possibility of a diminished antiviral response, caution is advised if bosentan is used concomitantly with nevirapine. Clinical and laboratory monitoring should be considered whenever bosentan is added to or withdrawn from therapy, and the nevirapine dosage adjusted as necessary. In addition, patients should be monitored for signs and symptoms associated with hepatotoxicity. Patients should be advised to seek medical attention if they experience potential symptoms of hepatotoxicity such as right upper quadrant pain, increasing abdominal size, fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, dark urine, pale stools, and jaundice.