Development of cytomegalovirus resistance to ganciclovir after oral maintenance treatment in renal transplant recipient

The emergence of a resistant strain is a theoretical threat after extensive use of antiviral drugs, We report the emergence of a ganciclovir-resistant cytomegalovirus (CMV) strain in a kidney transplant recipient during oral ganciclovir maintenance treatment. The patient was treated by oral ganciclo vir for 2 months after successful treatment of CMV primary infection by int ravenous ganciclovir, He developed a ne cv episode of CMV infection with no clinical response to intravenous ganciclovir, The CMV isolate exhibited bo th phenotypic and genotypic resistance to ganciclovir, The CMV isolate was constituted of a mixture of strains, with and without a mutation at codon 4 60 of the UL97 gene. The clinical condition improved when mycophenolate mof etil (MMF) was discontinued, and a short course of intravenous globulin was added to ganciclovir, The emergence of the CMV strain could be secondary t o more potent immunosuppression provide by MMF or subtherapeutic level obta ined during oral ganciclovir treatment. We believe that ganciclovir resista nce must be part of the differential diagnosis when a patient relapses or f ails to respond to ganciclovir treatment.