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 mana gement of immunocompromised hosts who have lesions that are poorly res ponsive to therapy with standard antiviral agents. We assessed the cor relation between the in vitro susceptibility result using a plaque red uction 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 resu lts and clinical responses were highly associated for both acyclovir a nd foscarnet (P < 0.001 and P < 0.001, respectively). The predictive v alues of a susceptible result (50% effective concentrations, < 2 mu g/ ml for acyclovir and < 100 mu g/ml for foscarnet) for complete healing of lesions were 62% for acyclovir and 82% for foscarnet; the predicti ve values of a resistant result for failure to heal were 95% for acycl ovir and 88% for foscarnet. Thus, in vitro testing has clinical utilit y in guiding therapy, although the 1 to 2 weeks required to derive a d efinitive result by the plaque reduction assay is a major limitation.