Sensitivity of herpes virus isolates from acyclovir clinical trials.

Clinical isolates of herpes simplex virus and varicella zoster virus have been examined for changes in drug sensitivity after treatment of patients with acyclovir. Some preliminary sensitivity results determined by plaque reduction assays in Vero cells for herpes simplex virus and MRC-5 cells for varicella zoster virus are presented. Where both pretreatment and posttreatment virus isolates were available, no significant changes in sensitivity to acyclovir were observed. Similarly, isolates taken after treatment was begun, without a pretreatment sample, gave IC50 values no greater than expected when compared with other pretreatment isolates.