AZT (3^I-azido 2^I, 3^I-dideoxy thymine) is used in the treatment of 

One of the problems in treating AIDS is that HIV can lie undetected in body cells. In addition, HIV can infect a variety of cells, including those in the central nervous system that are protected by the blood-brain barrier. Added to this is the problem of opportunistic infections, which may be very difficult to treat. Any therapy must overcome the problem that antiviral agents may also harm host cells. 

To date, four drugs with similar action are used to inhibit HIV replication and slow the progression of AIDS. All are nucleoside analogues, Substances that are similar to the naturally occurring nucleosides in RNA and DNA. They block conversion of retroviral RNA into DNA. The first and still most commonly used drug to treat AIDS is AZT (azidothymidine) or Retrovir.