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Drug-Specific Resistance

Summer 1999

A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!

In a time of rising HIV drug resistance and increasing treatment choices, the use of an HIV drug resistance test may help people living with HIV to make optimal therapeutic choices and avoid treatment failure caused by drug resistance.

While combination antiretroviral therapy has produced tremendous benefit for some people living with HIV, treatment failure now affects a growing proportion of people living with HIV/AIDS. Even with the increasing number of antiretrovirals available, many people do not achieve or maintain viral suppression.


Mutations

Many failures are linked to the increasing emergence of drug-resistant HIV, which is caused by the virus' extremely rapid rate of replication and mutation. The development of resistant mutations is a major cause of drug failure. HIV resistance can be defined as any change that allows viral replication in the presence of an inhibitor. Resistance results from an altered growth pattern (Phenotype) resulting from a change in viral Genotype.

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Geno & pheno "type"

Genotype is the genetic constitution or "gene type" of an individual. Phenotype is the physical manifestation of genes. (e.g., the Genotype of sickle cell anemia is HbsHbs and the Phenotype is that the red blood cells are sickle shaped).

HIV drug resistance testing can help people living with HIV and their physicians to make informed treatment choices. Drug resistance testing can be used to optimize antiretroviral therapy, provide cost effective individualized treatment strategies that result in improved long-term suppression of HIV, and help prevent the development of drug resistance.

There are two formats of HIV drug resistance tests, Phenotypic and Genotypic. Phenotype format advantages are that this assay (an assay is a test) measures direct drug sensitivity levels, mutational interactions, and variable drug response in people with HIV.

Genotype format advantages are that this assay detects new mutations, insertions, deletions by sequencing, has a 24-48 hour turnaround time for results, and is relatively lower in cost compared to Phenotyping.

Phenotype format disadvantages are that it tests one drug at a time so there is a longer turnaround time (weeks), relatively higher in cost than Genotyping. Genotype format disadvantages are that it employs an indirect method of resistance testing by searching for genetic mutations in a person's HIV that are already known to confer resistance.


Viral levels

The goal of HIV therapy is viral load suppression to undetectable viral levels. The tools to achieve this goal are the antiretroviral drugs currently available.

However, the introduction of new drug treatment strategies over the past decade has been followed by the emergence of resistant virus. Due to drug specific resistance and cross-resistance, the effectiveness of these medications is often reduced in people previously treated with antiretroviral therapy.

In addition, drug-resistant HIV may also be contracted by newly infected individuals. Thus, drug resistance testing is important in improving HIV therapy and enhancing the durability of drug therapy and viral load response.

Hopefully in the very near future, drug resistance testing, whether Phenotypic or Genotypic, will become part of the standard of care for HIV.

A large scale clinical trial to measure resistance is upcoming. Many individuals with HIV will be able to find out what they are resistant to by participating in the trial. Other than that -- you have to pay big bucks to get the test.

Ask your doctor where you can get a drug resistance test. Currently, the test is not widely available. Clinical trials and private insurance provide the best access.


A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!



  
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This article was provided by Women Alive. It is a part of the publication Women Alive Newsletter.
 
See Also
The Body's Guide to HIV Drug Resistance
HIV Mutations

Tools
 

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