Correlation between response to acyclovir and foscarnet therapy and in vitro susceptibility result for isolates of herpes simplex virus from human immunodeficiency virus-infected patients.

In vitro susceptibility testing of herpes simplex virus (HSV) isolates will play an increasingly important role in guiding the clinical management of immunocompromised hosts who have lesions that are poorly responsive to therapy with standard antiviral agents. We assessed the correlation between the in vitro susceptibility result using a plaque reduction assay in Vero cells and the response to antiviral therapy with acyclovir or foscarnet for 243 clinical isolates of HSV collected from 115 human immunodeficiency virus-infected patients. The in vitro results and clinical responses were highly associated for both acyclovir and foscarnet (P < 0.001 and P < 0.001, respectively). The predictive values of a susceptible result (50% effective concentrations, < 2 micrograms/ml for acyclovir and < 100 micrograms/ml for foscarnet) for complete healing of lesions were 62% for acyclovir and 82% for foscarnet; the predictive values of a resistant result for failure to heal were 95% for acyclovir and 88% for foscarnet. Thus, in vitro testing has clinical utility in guiding therapy, although the 1 to 2 weeks required to derive a definitive result by the plaque reduction assay is a major limitation.