Describe the best current medical defenses against viruses. Explain how AZT helps to fight HIV infections.?

(18-13)....

The best current medical defenses against viruses is in the prevention of viral transmission.

As far as anti-viral medications, it completely depends on what virus you are speaking about. For some viruses, we have no treatments that work and we have to treat symptoms as they appear. For other viruses, there are anti-virals which work.

Just like with antibiotics, anti-virals can work in different ways.

AZT (Zidovudine) is an anti-retroviral medication (active against retroviruses eg. HIV that contain RNA as their genetic material). In general terms, it is a nucleoside analog.

When HIV injects its "insides" into the host cell (usually a CD4+ cell) it is injecting (among other things):
-its genome (which is RNA)
-reverse transcriptase enzyme

For HIV RNA to be able to infect our cells and turn them into factories, it first has to change its RNA into DNA so that it can integrate with our DNA. To do this, HIV uses the reverse transcriptase enzyme that was also injected into the cell.\

AZT is a Nucleoside Reverse Transcriptase Inhibitor. It acts as a chain terminator and once it is incorporated, doesn't allow for further transcription. If HIV RNA cannot change fully into HIV DNA, it cannot permanently infect a cell.

In more detailed terms:

These are drugs that mimic the natural building blocks of DNA (nucleotides), however, once incorporated into the DNA chain by the HIV reverse transcriptase enzyme they do not allow additional nucleotides to be added and are hence named chain terminators or nucleotide analogues.

Chain terminators can be free of phosphate groups and are referred to as Nucleoside Reverse Transcriptase Inhibitors (NRTI) [eg AZT] or they can contain phosphate groups and are referred to as Nucleotide Reverse Transcriptase Inhibitors (written NtRTI) [eg tenofovir.] Once inside the cell they require three phosphate groups to be added to generate a nucleotide triphosphate which is the active form of the drug and is used as a substrate for reverse transcriptase during reverse transcription of viral RNA.

AZT acts as a nucleoside (thymidine) analog drug. It is in a class of drugs called reverse transcriptase inhibitors. Zidovudine is converted within the body to its active form (zidovudine triphosphate). This active form is similar to the compound thymidine triphosphate, a chemical needed by the HIV virus to make new DNA. The reverse transcriptase uses zidovudine triphosphate instead of thymidine triphosphate for making DNA, and it is the zidovudine triphosphate that interferes with the reverse transcriptase. Zidovudine does not kill existing HIV virus, and it is not a cure for HIV.