Isolation and characterisation of resistant Herpes simplex virus after acyclovir therapy.

Sensitivity of herpes simplex virus isolates to acyclovir became reduced in two bone-marrow transplant patients treated for established mucocutaneous infections. These isolates were thymidine-kinase-deficient mutants and were isolated within a week of discontinuation of a 1 week course of acyclovir therapy. The herpetic lesions in both patients continued to heal despite continued shedding of these viruses. Further studies and experience with this new class of antiviral agents are needed to determine the extent to which emergence of less sensitive virus will present clinical difficulties and to formulate treatment regimens that will minimise the emergence of such mutants.