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Still don't understand resistance risk
Apr 3, 2005

Two questions about resistance:

1. I am on successful treatment for hiv and would like the truth about whether I am at risk of contracting a resistant strain if I have unprotected male/male sex.

2. I have been on treatment for 5 years. Undetectable for 4.5 yrs, cd4s at 1000 for about that period, 43% cd4 ration. I am fully adherent to medication. What are the chances of the virus becoming resistant if I am fully adherent? Is resistance inevitable at some point and if so is there any way of predicting how long before a change of meds will be required.

Many thanks for your help.


Response from Dr. Sherer

The truthful answer to number one is that you are at risk of acquiring a resistant strain if you have unprotected male/male sex. While it has been surprisingly difficult to prove that superinfection occurs, recent evidence is quite clear that it can happen. At the recent retrovirus conference, a cohort from Mombasso was analyzed over time, and several patients where shown to have acquired a new virus, e.g. a clade D virus in a patient with clade C, or clade A/C in a patient with clade C. In another analysis from San Francisco, superinfection was found in 4 of 104 recently infected subjects (3.8%), or 2.1/100 person-years (95% CI: 0.6, 5.2).

Importantly, some of the cases in the US, with a new clade B strain acquired in one with another B strain, were identified due to a sudden loss of virologic control due to a newly acquired resistant strain.

So it can happen, at a low frequency. Your best protection from this outcome is to continue to practice safe sex.

It's not possible to put a number to the likelihood that an individual who has an excellent virologic response for a long period of time, as you have, will develop resistance.

These are the facts that define the uncertainty. Through the use of 'ultrasensitive' resistance tests, that can detect minority species down to 0.1% of circulating virus, rather than the 20% limit with conventional resistance testing, that there is continual viral evolution, even in patients with excellent control. Mutant virions continue to be produced at low frequency.

It appears that an optimal three drug HAART regimen usually prevents these minority populations from becoming the dominant circulating strain, with the result being the development of virologic failure.

However, it is not uncommon for patients with excellent adherence and an effective regimen for long periods of time to eventually develop resistance.

Its not possible to categorize this process as inevitable, since there are still many patients who remain well-controlled on their first regimen for 7 years or more.

Your best actions, in light of this uncertainty, is to continue with your excellent adherence.

I urge you to talk with your doctor about these questions and responses.

Reason to switch to TZV + TFV ?

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