Polymerase chain reaction-based ganciclovir-resistance testing of ocular fluids for cytomegalovirus retinitis

Cytomegalovirus (CMV) retinitis typically presents as a hemorrhagic, full-thickness retinitis in immunosuppressed individuals, often in the setting of HIV infection. The management of CMV retinitis includes systemic and locally administered intravitreal antivirals (i.e. foscarnet or ganciclovir), as well as the surgical intravitreal ganciclovir implant. In chronically immunosuppressed patients (i.e. transplant recipients, cancer chemotherapy) and in HIV/AIDS patients who fail to immune reconstitute, chronic CMV prophylaxis with valganciclovir may lead to ganciclovir- and foscarnet-resistant CMV strains. Moreover, the identification of drug-resistant CMV may influence the choice or dosing of antiviral medication.1–2 Ganciclovir-resistance is classified into genotypic resistance defined as CMV DNA harboring a mutation known to confer antiviral resistance or phenotypic resistance meaning that ganciclovir at a therapeutic dose fails to exceed the concentration required to inhibit 50% of CMV growth on viral culture media. We characterize a series of patients with CMV retinitis who were evaluated for genotypic ganciclovir-resistance using PCR-based analysis of ocular fluids and describe its influence on management.