Used primarily to treat cytomegalovirus (CMV) infections, especially in immunocompromised patients such as those with HIV/AIDS or who have undergone organ or bone marrow transplants. It is effective in managing CMV retinitis, a viral infection of the retina that can lead to blindness. Administered intravenously, orally, or via intraocular implant, ganciclovir works by inhibiting viral DNA replication. It is also used prophylactically in transplant recipients at high risk for CMV disease. Due to potential toxicity, including bone marrow suppression, its use requires careful monitoring.