Multiplicity dependence and sensitivity of herpes simplex virus isolates to antiviral compounds.

An immunoassay that enables one to assess both viral multiplicity and sensitivity to antiviral drugs, was used to determine the sensitivity of untreated patients' virus isolates. The upper border levels for judging clinical isolates sensitive to Ara-A, ACV, PFA or IDU were calculated from a total of 48 primary herpes simplex isolates. Although five isolates were considered less sensitive to one drug and one isolate to two drugs, all were sensitive at a lower virus multiplicity. Analysis of these isolates showed that no isolate was genetically resistant, but that multiplicity dependence of drugs was high with ACV and Ara-A, lower with PFA. In view of the multiplicity dependence of HSV sensitivity to different drugs, it is recommended that isolates from treatment failures or isolates considered resistant should be assayed in detail.