The FDA has notified healthcare professionals that drug interactions between the hepatitis C virus (HCV) protease inhibitor Victrelis (boceprevir; Merck) and certain ritonavir-boosted human immunodeficiency virus (HIV) protease inhibitors can potentially reduce the effectiveness of these medicines when they are used together. A drug-interaction study showed that taking Victrelis with ritonavir (Norvir) in combination with Reyataz (atazanavir; Bristol-Myers Squibb), Prezista (darunavir; Janssen Therapeutics), or Kaletra (lopinavir/ritonavir; Abbott) reduced the blood levels of the HIV medicines and Victrelis in the body.

In the study, Victrelis reduced mean trough concentrations of ritonavir-boosted Reyataz, Prezista, and Kaletra by 49%, 43%, and 59%, respectively. Mean reductions of 34–44% and 25–36% were observed in area under the curve (AUC) and peak concentration (Cmax) of Reyataz, Prezista, and Kaletra. Co-administration of ritonavir-boosted Reyataz with Victrelis did not alter the exposure (AUC) of Victrelis, but co-administration of Victrelis with Kaletra or ritonavir-boosted Prezista decreased the AUC of Victrelis by 45% and 32%, respectively.

The FDA and Merck are updating the Victrelis drug labeling to include information about these interactions. Victrelis is a HCV NS3/4A protease inhibitor indicated for the management of chronic hepatitis C genotype 1 infection in combination with other therapies. Reyataz, Prezista, and Kaletra are HIV protease inhibitors indicated for the treatment of HIV-1 infection. Healthcare professionals who have initiated Victrelis in combination with peginterferon alfa and ribavirin in HIV-HCV co-infected patients on fully suppressive antiretroviral therapy containing a ritonavir-boosted protease inhibitor should discuss these findings with those patients, and closely monitor those patients for HCV treatment response and for potential HCV and HIV virologic rebound.

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