Ganciclovir is an antiviral medication primarily used to treat infections caused by the cytomegalovirus (CMV), particularly in individuals with weakened immune systems, such as those with HIV/AIDS or organ transplant recipients. It works by inhibiting viral DNA synthesis, thereby slowing down the replication of the virus. This medication is typically administered intravenously or orally, depending on the severity of the infection. Common side effects may include nausea, diarrhea, and bone marrow suppression, which can lead to decreased blood cell counts. Regular monitoring is essential during treatment to manage any potential complications.