Interim results from an ongoing Phase 2 clinical trial indicate that the hepatitis C drug Victrelis, in combination with peginterferon and ribavirin, resulted in twice as many HIV-positive patients achieving undetectable hepatitis C virus levels than peginterferon and ribavirin alone.

“We are encouraged by these interim results with Victrelis in combination therapy in this difficult-to-treat patient population,” said Dr. Roger Pomerantz, senior vice president of Infectious Diseases at U.S. pharmaceutical company Merck, in a press release.

Based on the results, Dr. Pomerantz said that Merck is planning to initiate a Phase 3 study of Victrelis in people with both HIV and hepatitis C later this year.

The results were presented last week at the Infectious Diseases Society of America 2011 Annual Meeting in Boston.

Hepatitis C is a liver disease caused by the hepatitis C virus. If untreated, infection with the hepatitis C virus can cause damage and scarring to the liver, liver cancer, and eventually liver failure. Once the liver fails, a liver transplant is necessary for a patient to survive. Some people who are infected can spontaneously clear the virus themselves; the rest need treatment with antiviral drugs.

HIV patients with hepatitis C are less likely to clear the infection compared to patients with hepatitis C only. Once the infection develops and becomes chronic, HIV patients are less likely to respond to hepatitis C treatment, which currently consists of peginterferon-alfa  (PegIntron, Pegasys) plus ribavirin (Rebetol, Copegus) for 48 weeks.

Victrelis (boceprevir) was approved by the United States Food and Drug Administration in May of this year for the treatment of hepatitis C, in combination with peginterferon-alfa and ribavirin. However, it was not approved at the time for people with both HIV and hepatitis C, due to lack of information on efficacy in people who are co-infected.

In this ongoing Phase 2 study, researchers are comparing the efficacy of Victrelis plus PegIntron (peginterferon alfa-2b) and ribavirin to PegIntron and ribavirin alone in adult patients with both hepatitis C and HIV.

The study includes 98 participants who were randomly assigned to receive one of the two above mentioned treatments. All participants had stable HIV infections, were receiving an optimized antiretroviral regimen, and had not previously been treated for hepatitis C.

Since studies have shown that certain HIV antiretrovirals may potentially interact with Victrelis, non-nucleoside reverse transcriptase inhibitors, zidovudine (Retrovir), stavudine (Zerit), and didanosine (Videx) were not allowed during the study.

Most participants were Caucasian (82 percent), and a majority were male (69 percent). The median participant age was 43 years old.

Participants in each of the two treatment groups received four weeks of treatment with PegIntron plus ribavirin. Two-thirds of the participants then initiated treatment with Victrelis three times daily in addition to PegIntron and ribavirin; the remaining participants continued treatment with just PegIntron plus ribavirin.

Results showed that after 24 weeks, 70 percent of participants taking Victrelis had undetectable hepatitis C virus levels, compared to 34 percent of participants taking PegIntron and ribavirin alone.

The most common side effects in the group receiving Victrelis versus the group receiving PegIntron and ribavirin alone were: low white blood cell levels (neutropenia), 13 percent versus 3 percent; bad taste in the mouth, 25 percent versus 15 percent; vomiting, 25 percent versus 15 percent; fever, 34 percent versus 21 percent; headache, 28 percent versus 12 percent; and decreased appetite, 30 percent versus 18 percent.

Serious side effects occurred in 8 percent of the patients receiving Victrelis in combination with PegIntron and ribavirin, compared with 21 percent of patients receiving PegIntron plus ribavirin alone.

Overall, 14 percent of participants receiving Victrelis discontinued treatment due to side effects, compared to 9 percent of participants receiving PegIntron and ribavirin alone.

The trial will continue for an additional 24 weeks. Merck stated that final results are expected in 2012.

For more information, please see the study (abstract) or the Merck press release.