Which medication is classified as an antiviral?

Acyclovir is classified as an antiviral medication because it is specifically designed to treat infections caused by certain viruses. It primarily targets the herpes simplex virus, which is responsible for conditions such as genital herpes, cold sores, and shingles (herpes zoster). Acyclovir works by inhibiting the replication of viral DNA, which helps to control and lessen the severity of these viral infections.

In contrast, the other medications listed serve different purposes. Fluconazole is an antifungal drug used to treat fungal infections, Metronidazole is an antibiotic effective against certain bacterial and parasitic infections, and Citalopram is an antidepressant that belongs to the selective serotonin reuptake inhibitors (SSRIs) class, primarily used for treating depression and anxiety disorders. Thus, Acyclovir stands out as the appropriate choice due to its specific antiviral action.