Merck urged the FDA to look into potential safety concerns as the agency seeks to widen patient eligibility criteria for oncology drug trials of HIV, hepatitis B and hepatitis C patients.

In a comment on the agency’s draft guidance on expanding trial eligibility criteria, the drugmaker agreed that more patients with HIV, HCB and HCV should be included in cancer drug clinical trials. But Merck cited concerns over immuno-oncology (IO) drugs because of the potential for serious immune reactions and impacts on liver function in patients with active viral infection.

“The added benefit of having expanded patient eligibility criteria…must be weighed against the potential safety risks for such patients regarding exposure to an IO drug,” the company said. Starting therapy for HCV could cause adverse events when coinciding directly with other IO therapies, Merck noted.

Including patients co-infected with HBV/HCV in an IO drug trial has its own complexities because of the “known interaction” between the two viruses during co-infection, Merck said.