Which antiviral agent is commonly used to treat cytomegalovirus (CMV) infections?

Ganciclovir is the antiviral agent commonly used to treat cytomegalovirus (CMV) infections due to its specific mechanism of action against this virus. Ganciclovir is a synthetic analog of guanosine, and it works by inhibiting viral DNA synthesis. This inhibition is particularly effective against CMV, which can cause serious infections in immunocompromised individuals, such as transplant recipients and those with HIV/AIDS.

In the case of CMV, ganciclovir is preferred because it is selectively phosphorylated by viral enzymes, which enhances its activity against CMV while minimizing effects on normal human cells. The effectiveness of ganciclovir makes it a key therapeutic option in managing CMV retinitis and other manifestations of CMV disease.

Other antiviral medications listed serve different purposes; for example, oseltamivir is primarily used for treating influenza, ribavirin is employed for hepatitis C and some viral hemorrhagic fevers, and valacyclovir is mainly effective against herpes simplex and varicella zoster viruses. Therefore, these alternatives are not suitable for CMV infections, reinforcing why ganciclovir is the correct choice.