Ganciclovir-resistant cytomegalovirus infection in renal transplantation

Cytomegalovirus (CMV) infection is an important cause of morbidity in renal transplant recipients, due to both direct and indirect effects of the virus on the graft and patient [1]. Ganciclovir (GCV) remains the most common first-line therapy, but its low oral bioavailability was identified as a risk factor for the emergence of resistant strains [1], and intravenous (IV) administration is inconvenient for use in prophylactic or pre-emptive therapy. Valganciclovir (VGCV) is a prodrug of GCV with a much higher oral bioavailability, which makes it very useful for prophylaxis and preemptive therapy, as well as for treatment in selected patients [2–4]. Although initially associated with a negligible risk of drug resistance [5], subsequent papers identified patients with GCV-resistant CMV infection after VGCV prophylaxis and treatment [6, 7]. Patients with drug-resistant CMV strains often have more tissue-invasive disease and unfavourable clinical outcomes [8, 9], but there is some heterogeneity, and reports of asymptomatic infection, particularly in nonlung transplant recipients, suggest that some mutations are less pathogenic than others [10]. The therapeutic approach is a challenge and must balance the severity of the infection against the risks of drug toxicity and reduction of immunosuppression. We report two cases of GCV-resistant CMV from our unit: the first is a case of invasive CMV disease in a low-risk renal transplant recipient while on therapy with VGCV, and the second is a high-risk patient who developed GCVresistant CMV infection while on VGCV prophylaxis.