Abacavir is an antiviral medication used primarily to treat HIV infection. It belongs to a class of drugs known as nucleoside reverse transcriptase inhibitors (NRTIs), which work by blocking the reverse transcriptase enzyme, preventing the virus from replicating in the body. This medication is often combined with other antiretroviral drugs to create a comprehensive treatment regimen. Abacavir is available in tablet and liquid forms and is typically taken once or twice daily. Patients must be tested for the HLA-B*5701 gene before starting treatment, as those with this gene are at a higher risk for serious allergic reactions.