A nucleoside analogue used to slow replication of HIV. AZT is approved for the initial treatment of HIV infection. AZT is increasingly administered in combination with other antiviral drugs, especially 3TC (a combination that is under consideration by the FDA as another initial treatment regimen for HIV) as well as ddC (an FDA-approved combination for persons with progressive disease and CD4 cell counts below 300). Possible side effects include bone marrow suppression leading to anaemia, leucopoenia or neutropenia nausea, muscle weakness and headaches.