US pharma giant Merck & Co (MSD in Europe) has warned that its hepatitis C drug Victrelis (boceprevir) significantly reduces the effectiveness of some major HIV medications.
Trials have shown that Victrelis, which was approved by the European Commission in July 2011 as part of a triple combination therapy for liver disease, has been shown to reduce blood levels of the protease inhibitors Reyataz, Prezista and Kaletra by around half.
The efficacy of Victrelis is also severely reduced by these drugs.
Since an estimated 10–15% of patients with hepatitis C also have HIV, the finding is likely to affect sales of Victrelis significantly.
In a letter to US healthcare professionals, Merck said: “These drug interactions may be clinically significant for patients infected with both chronic hepatitis C virus and HIV by potentially reducing the effectiveness of these medicines when co-administered.”
Hepatitis C affects up to 300 million people worldwide, causing long-term and potentially fatal liver damage.
Merck and Roche have co-promoted a triple combination therapy for Hepatitis C consisting of Victrelis, peginterferon alfa and ribavirin in Europe, Asia and Latin America following the EC approval.
The drug interaction study, which used healthy volunteers, showed that Victrelis reduced blood levels of Reyataz (atazanavir), Prezista (darunavir) and Kaletra (lopinavir/ritonavir) by 49%, 59% and 43% respectively.
Levels of Victrelis itself were reduced by 45% when taken with Kaletra and by 32% when taken with Prezista.
According to ISI Group analyst Mark Schoenebaum, the drug interaction findings could reduce sales of Victrelis by as much as 25%.
Merck is conducting further drug-interaction studies of Victrelis with other HIV drugs, including Intelence (etravirine) and Isentress (raltegravir).