Zidovudine is a nucleoside analog reverse-transcriptase inhibitor (NRTI), a type of antiretroviral drug used for the treatment of HIV/AIDS infection.AZT was the first breakthrough in AIDS therapy, significantly reducing the replication of the virus in patients and leading to clinical and immunologic improvements. It can also be used to prevent HIV transmission, such as from mother to child during the period of birth or after a needle stick. Used by itself in HIV-infected patients, AZT safely slows HIV replication in patients, but generally does not stop it entirely. This may allow HIV to become AZT-resistant over time, and for this reason AZT is now usually used in conjunction with the other anti-HIV drugs in combination therapy called highly active antiretroviral therapy (HAART). AZT crystallizes into an asymmetric nucleated monoclinic salt structure, forming an equalized hydrogen-nitrogen-oxygen bonded network of base-paired dimers.