Ganciclovir and valganciclovir are first-line treatments for cytomegalovirus in immunocompromised children; however, the optimal therapeutic target remains unclear. This review identified 6 studies that showed clearance of cytomegalovirus viremia occurs with a median area under the concentration-time curve (AUC 24 ) between 23 and 70 μg·h/mL, with no clear correlation with efficacy or toxicity.