In simple terms, drug resistance refers to the ability of disease-causing germs—such as bacteria and viruses—to continue multiplying despite the presence of drugs that usually kill them.
With HIV, drug resistance is caused by changes (mutations) in the virus's genetic structure. These mutations can lead to changes in certain proteins, most commonly enzymes, that help HIV reproduce (replicate).
Mutations are very common in HIV. This is because HIV replicates at an extremely rapid rate and does not contain the proteins needed to correct the mistakes it makes during copying.
Mutations occur randomly, on a daily basis, but many are harmless. In fact, most mutations actually put HIV at a disadvantage—they reduce the virus's "fitness" and slow its ability to infect CD4 cells in the body. However, a number of mutations can actually give HIV a survival advantage when HIV medications are used, because these mutations can block drugs from working against the HIV enzymes they are designed to target. These are the mutations we are concerned about when we talk about drug resistance.
HIV relies on many enzymes to replicate inside a human cell. It also relies on proteins, including gp41, to latch on to CD4 cells and infect them. Mutations can occur in any of these parts of the virus and cause drug resistance:
For people infected with HIV, drug resistance can render drugs less effective or even completely ineffective, thus significantly reducing treatment options.
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