Drug Resistance - Part 1

Recent studies identify an alarming increase in drug resistant strains of HIV, and concerns are growing about the sustainability of HIV treatment programs at home and abroad. Researchers estimate that international levels of drug resistance range from 5% to 30%, up from about 1% to 5% ten years ago.1 Among certain high-risk populations, drug resistance estimates are as high as 80% according to research published by the International AIDS Society.2 Furthermore, unexpected costs associated with monitoring and responding to drug resistance could double the amount of funding the United Nations has designated as necessary to address HIV/AIDS worldwide, funding that is already facing significant cuts and uncertainty.

In the first of this 2-part series on drug resistance, we start with the basics: What is drug resistance and how does it happen?

Mistakes & Mutations

Drug resistance means that medications to control HIV cease being effective. The easiest way to understand drug resistance starts with an explanation of how HIV functions. Like all viruses, HIV’s singular goal is to find a host and replicate. HIV hijacks human immune system cells, changes their genetic instructions, and turns them into virus-making factories. Without treatment, HIV is capable of producing billions of copies in a single day. Newly formed viral copies go on to infect additional cells, produce new copies, and so on. However, a factory trying to produce billions of copies of anything is likely to make some mistakes along the way.

As the HIV factory churns away it makes a lot of mistakes. Mistakes result in new forms of virus that are slightly different than the original; these changed viral copies are called mutations. While most mutations are harmless, some will change in just the right way to resist anti-HIV drugs (also known as ARVs). These mutations are perfectly natural and completely accidental. Ironically, drug resistance happens because HIV is not very good at doing its job.

Missed Doses = More Mutations

ARVs work by limiting HIV’s ability to replicate. Fewer copies of HIV in the body mean less potential to damage the immune system. Fewer copies of HIV also mean less chance of mutations. If a person takes ARVs as prescribed and without missing doses, viral replication is curbed.

However, even a few missed doses allow the amount of new virus to increase quickly. More copies of virus means a greater chance of developing drug-resistant mutations. When ARVs are resumed, the drug-resistant mutations are able to survive and replicate. The new strain will eventually become the predominant or most common type of HIV in the body. The current ARV (and possibly an entire class of ARVs) will no longer be able to control the virus.

Click here for part two where we cover current findings of drug resistance studies in San Francisco and the implications being reported internationally.


Sources:

1. In South Africa, Drug resistant HIV Emerging. Retrieved February 9, 2010 from
   http://www.msnbc.msn.com/id/34624393/ns/health-aids//
2. In South Africa, Drug resistant HIV Emerging. Retrieved February 9, 2010 from
   http://www.msnbc.msn.com/id/34624393/ns/health-aids//