Interesting results of a trial that looked at the Pre-Exposure Prophylaxis (PrEP) – essentially uninfected people taking a drug prophylactically – on new infections from HIV were released earlier today in the New England Journal of Medicine. Roughly 2500 male and transgender men who have sex with men (high risk uninfected) in the Americas, South Africa, and Thailand were randomized to receive a once daily combination pill of emtricitabine and tenofovir disoproxil fumarate (FTC–TDF). After about a year and a half, about 100 people developed new infections from the virus but the treatment group experienced a roughly 44% decreased risk of new infection. This is pretty exciting news, as there is a clearly the need for new effective methods to prevent HIV.
I know it is coming…so I’ll weigh in on this question. So if this works, why not just distribute the drugs to everyone in highly affected countries? While exciting news, I think there are a number of drawbacks of that might prevent this approach from being more widely adopted at the general population level.
First, these are heavy drugs, the trial itself found relatively high levels of adherence problems, and I am not an expert in this but I’ve always had the impression that most ART drugs are not the kind of thing people want to be taking unless the alternative (death) is severe.
Second, we need to consider the whether this represents a good use of resources. This trial was conducted in a very high risk population and even then the risk reduction was only about half. Depending on how costly these drugs would be, plus the associated medical costs of ensuring some medical follow-up of people taking these drugs, it might not be cost-effective relative to other prevention strategies in the general population.
Third, we must also consider drug resistance. Although no drug resistance was detected among those patients who developed HIV during the trial, resistance to these particular medicines can be developed and could potentially have widespread effects on overall usefulness of ART medicines.
Fourth, we must also consider the behavioral effect of these drugs on patients. The overall trial would have picked up short-term behavior effects (e.g. if people think they are protected they may engage in more or more risky sexual behavior) but we should worry about is the more long term effects of this intervention on behavior, say over time or outside of a trial setting. Depending on how large this effects might be, it could undermine the overall effectiveness of the strategy.
Finally, PrEP is not a magic bullet. There are other ways of becoming infected that are unlikely to be affected by this drug (e.g. injections) and the reduction was far from complete. Plus, unlike other prevention methods (e.g. condoms) it does little to protect against other STIs.
But of course anything that helps in preventing this horrible disease, even a bit, is very good news.
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