WHAT IS RESISTANCE?

WHAT IS RESISTANCE?

HIV is "resistant" to a drug if it keeps multiplying rapidly while you are taking the drug. Changes (mutations) in the virus cause resistance. HIV mutates almost every time a new copy is made. Not every mutation causes resistance. The "wild type" virus is the most common form of HIV. Anything different from the wild type is considered a mutation.

An antiretroviral drug (ARV) won?t control a virus that is resistant to it. It can "escape" from the drug. If you keep taking the drug, the resistant virus will multiply the fastest. This is called "selective pressure."

If you stop taking medications, there is no selective pressure. The wild type virus will multiply the fastest. Although tests may not detect any drug resistance, it might come back if you re-start the same drugs.

Resistance testing helps health care providers make better treatment decisions for their patients.

HOW DOES RESISTANCE DEVELOP?

HIV usually becomes resistant when it is not totally controlled by drugs someone is taking. However, more people are getting infected with HIV that is already resistant to one or more ARVs.

The more that HIV multiplies, the more mutations show up. These mutations happen by accident. The virus doesn’t "figure out" which mutations will resist medications.

Just one mutation can make HIV resistant to some drugs. This is true for 3TC (Epivir) and the non-nucleoside reverse transcriptase inhibitors (NNRTIs). However, HIV has to go through a series of mutations to develop resistance to other drugs, including most protease inhibitors.

The best way to prevent resistance is to control HIV by taking strong ARVs. If you miss doses of your medications, HIV will multiply more easily. More mutations will occur. Some of them could cause resistance.

If you have to stop taking any ARV, talk to your health care provider. You may have to stop some drugs sooner than others. If you stop taking drugs while the virus is under control, you should be able to use them again.