Comparative efficacy of antiherpes drugs against various strains of varicella-zoster virus.

Twenty antiherpes compounds were compared for their inhibitory activities against five laboratory strains and five clinical isolates of varicella-zoster virus (VZV) in human embryo fibroblast cultures. E-5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil (BVaraU), E-5-(2-iodovinyl)-2'-deoxyuridine (IVDU), and E-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) were the most effective. The average values of the 50% inhibitory dose (ID50) for VZV replication were 0.0013, 0.0015, and 0.0024 micrograms/ml, respectively. 1-beta-D-Arabinofuranosyladenine and 9-(2-hydroxyethoxymethyl)guanine were 1.2 and 3.4 times less effective than 5-iodo-2'-deoxyuridine (IDU). The selectivity indexes (ratio of ID50 for host-cell DNA synthesis to ID50 for VZV replication) of BVaraU, IVDU, and BVDU were between 41,000 and 67,000, whereas those of cytosine arabinoside, IDU, and 5-bromo-2'-deoxyuridine were less than 1.1. BVaraU, IVDU, and BVDU were the most potent and the most selective inhibitors of VZV activity. A deoxythymidine kinase deficient mutant of VZV was resistant to most of the compounds tested at concentrations up to 36,000 times greater than the average ID50 for strains that were not deficient.