Zidovudine (AZT) was approved for the treatment of Human Immunodeficiency Virus (HIV) infection in 1987. This drug was first synthesized in 1964 but proved ineffective as a cancer chemotherapeutic. It was abandoned until its activity against retroviruses was discovered by an American reserach group in 1986, and was approved for marketing by the FDA in 1987.
AZT and related nucleoside drugs inhibit viral replication by targeting specific viral enzymes. Because of the rapid development of drug resistance first demonstrated with AZT, monodrug therapy is no longer used to treat HIV infection.