Pre-Exposure Prophylaxis: Failure :-(

11 02 2009

News of the great white hope, Pre-Exposure Prophylaxis, for the prevention of HIV:

A new mathematical model of PrEP use in U.S. populations at high risk for HIV infection takes these and other questions into account and predicts the prevention strategy could substantially reduce the lifetime risk of HIV infection. According to the model, the cost-effectiveness of PrEP could vary substantially depending on the age of the target population, their risk behaviors, the annual rate of new HIV infections in the target population, and the efficacy and cost of antiretroviral PrEP drugs. These findings are reported by a team of scientists led by A. David Paltiel, Ph.D., of Yale University, and supported by the National Institute of Allergy and Infectious Diseases (NIAID), the National Institute of Mental Health and the National Institute on Drug Abuse, all part of the National Institutes of Health.

Dr. Paltiel says his team’s model is the first to establish performance benchmarks that clarify the clinical, epidemiologic and economic circumstances under which PrEP would represent good patient care, good public health and good value.

To create their model, the researchers made several conservative assumptions: 1) PrEP is 50 percent effective; 2) the target population is American men who have sex with men who average 34 years of age; 3) 1.6 percent of this population becomes newly infected with HIV annually; and 4) the antiretroviral drugs (tenofovir and emtricitabine) cost $9,000 per year. With these parameters, the model predicts PrEP would cut the lifetime risk of HIV infection from 44 percent to 25 percent.

However, the life expectancy of the target population from the time after beginning PrEP would increase by less than a year (from 39.9 years to 40.7 years) and PrEP would not be cost-effective by current U.S. standards. Yet with modest improvements in the efficacy of antiretrovirals used preventively, more realistic estimates of their cost (potentially as low as $900 per year), or a target population that is younger and at higher risk, the model predicts PrEP might be as cost-effective as other widely recommended public health and medical interventions in the United States. With large improvements in these parameters, the potential benefits of PrEP could be substantial, according to the model. For example, assuming PrEP will be 90 percent effective leads the predicted lifetime risk of HIV infection to fall from 44 percent to 6 percent.

First take: a couple of notable things: we are assuming only a 50% effectiveness rate (first). Second, we are looking at a price of $900-$9000 a year, to only add (third) an average of less than one year of lifespan to the target population while only (fourth) decreasing the risk of infection by 19%.

So… tell me about those crazy new things called “condoms” again???

What’s disappointing is that I thought the news would be more positive — that is, I was sure that there would be greater effectiveness (I’ve heard numbers as high as 80%), and I was sure that models would indicate a dramatic shift in infection.

The problem, of course, at this point, is that since HIV/AIDS has become somewhat of a manageable — if still awful — disease in this country, that these numbers don’t look cost effective for funding PrEP — even research! Who’s going to fund something that, in the end, gives absolutely no return on their investment? The CDC could, I suppose, under the guise of “for use in foreign countries” or “gauge the true efficacy,” but I’m going to bet that they will still have difficulty justifying it.

I’m more upset about the background data, and not so much about the mathematical model they created.

I thought it would be better.

I wonder what happened to all those people that Canada handed Truvada to at the Gay Games last summer as a PrEP.

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