Antiviral Therapy

Many studies have incorporated antiviral nucleoside analog drugs such as acyclovir and ganciclovir. The nucleosides require conversion to the monophosphate form by the viral enzyme TK. Additional phosphoryla-tions are then performed by cellular kinases. Acyclovir or ganciclovir triphosphates are then preferentially incorporated into DNA by viral DNA polymerase, where they then act as obligate chain terminators. However, TK and viral DNA polymerase are enzymes that are only expressed during lytic infection, while EBV-PTLD is thought to result from latently infected proliferating B cells. Hence, no effect of these drugs would be expected with respect to the prevention or treatment of PTLD. Nevertheless, acyclovir is often instituted when EBV-PTLD is diagnosed, but there is scant information documenting the effectiveness of either acyclovir, ganciclovir, or newer antiviral agents such as cidofovir.11 Despite a paucity of data supporting the merits of using antiviral therapy in this setting, the European Best Practice Expert Group on Renal Transplantation suggests that in the case of EBV-posi-tive B-cell lymphomas, antiviral treatment with acy-clovir, valacyclovir, or ganciclovir may be initiated for at least 1 month or according to the blood level of EBV replication when available.59

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