Inhibition of human herpesviruses by combination of acyclovir and human leukocyte interferon

Human leukocytes interferon in low concentrations (1 to 5 U/ml) enhanced the antiviral effect of acyclovir against herpes simplex virus, varicella-zoster virus, and cytomegalovirus grown in human fibroblasts. This occurred without additive inhibition of the division of human fibroblasts or proliferation of peripheral blood mononuclear cells. The combined antiviral effect was additive against clinical isolates of cytomegalovirus and was synergistic against clinical isolates of the other two viruses. The magnitude of the effect with cytomegalovirus was the same when laboratory and wild-type virus were compared. The persistence of varicella-zoster virus in the presence of acyclovir in infected human cells was also reduced by the addition of interferon.