The Food and Drug Administration warned Friday that doctors should not prescribe and patients should not use the hepatitis C drug Victrelis (boceprevir) and the anti-HIV drug ritonavir at the same time because such use reduces the effectiveness of both drugs. Patients already using the two drugs simultaneously should not stop taking them without consulting their doctor, however, the agency cautioned. Ritonavir, a protease inhibitor, is commonly used to boost the effectiveness of other protease inhibitors and is found in Reyataz (atazanavir/ritonavir), Prezista (darunavir/ritonavir) and Kaletra (lopinavir/ritonavir).
Clinical trials have shown that using the two drugs simultaneously reduces the level of both compounds circulating in the blood and can thus lead to a virologic rebound in which the HIV virus develops resistance to the drugs. A similar effect has been observed with the recently approved hepatitis C drug Incivek (telaprevir), and a warning already appears on the label of that drug. A warning against co-use of the drugs will now be placed on Victrelis' label.