Abacavir is an antiviral medication used to treat HIV (human immunodeficiency virus) infection. It belongs to a class of drugs known as nucleoside reverse transcriptase inhibitors (NRTIs), which work by blocking the virus's ability to replicate in the body. Abacavir is often combined with other antiretroviral medications to enhance its effectiveness. Patients taking abacavir must be tested for the HLA-B*5701 gene, as those who carry this gene are at a higher risk of developing serious allergic reactions. Common side effects may include nausea, headache, and fatigue. Regular medical check-ups are essential to monitor the treatment's effectiveness and any potential side effects.