Explain how the drug AZT(aidothymidine) can help patients with aids.?

It blocks the enzyme reverse transcriptase.

Technically, AZT falls into the class of viral inhibitors known as nucleotide analogs. AZT mimics normal nucleotides, and the reverse transcriptase incorporates them into DNA synthesis. The differenece between AZT and normal nucleotides is that AZT stops any further extension of the DNA. This is what cuts down HIV replication.

AZT administration can decrease mortality and the frequency of opportunistic infections

AIDS is caused by the Human Immunodeffieciency Virus (HIV). This virus is a so called "Retrovirus", this means that rather than using DNA to code for its genes it uses RNA. Upon infection of a cell the virus must turn its RNA into DNA in order to insert its genes into the host cells genetic material. In order to do this it uses the enzyme reverse transcriptase. AZT works by inhibiting the action of this enzyme and thus dramatically slowing viral replication.

This slowing of replication slows the progression of the disease and reduces the morbitiy of the disease. It is not a cure for HIV however, eventually even with AZT (and other reverse transcriptase inhibitors) the disease universally progresses to full blown AIDS. AIDS itself, however, is not the usual cause of death, but while heavily immunocompromised (as a result of the immune system being wiped out by the disease) other infections (and indeed cancers such as Kaposi's sarcoma) will ultimately cause death. Frequently the infected person will succumb to pneumonia.

HIV is able to become resistant to AZT and as such AZT is normally used in combination with other drugs to avoid this.

Most importantly, there is no cure for AIDS, only prevention. As I am sure most people are aware the greatest risk factor for this disease is through sexual contact, so if you are sexually active you should either have an HIV test if you are in a relationship, or lternatively use a condom.