Posts Tagged ‘absolute risk reuction’

The Cost of Truvada Pre-exposure prophylaxis, PrEP

August 17, 2011 1 comment

In my last post I wrote about the very small reduction in the absolute risk of HIV infection in the iPrEx trial among those taking Truvada  as pre-exposure prophylaxis.

The 44% reduction in relative risk conferred by Truvada was the only efficacy measurement explicitly presented by the investigators.  That the absolute risk reduction was only 2.3% was not mentioned in the various presentations.

I suspect that many reading press reports of this so called breakthrough were unaware that in fact, the actual risk to people taking Truvada was 2.8%.  (36 infections in 1251 participants).  True, this is less than the 5.1% risk to those on placebo, but by very little.  Certainly not enough to justify the bewildering acclaim given to the iPrEx trial results.

Failing to clearly state the absolute risk reduction of an intervention is something we have come to expect from salesmen to inflate the efficacy of a product, but not from clinical researchers.  Large reductions in relative risk can be associated with minute reductions in absolute risk when the events prevented are low to begin with.

Another important reason why absolute risk reduction should be stated in a report is that this allows one to calculate the number of people who need to be treated to prevent one event, in this case, one HIV infection.

Although the iPrEx investigators did not explicitly provide these numbers, they can be worked out from data presented, as I did in my last post and was also done in a letter published in the New England Journal of Medicine of April 7, 2011 in response to the iPrEx trial report, where the authors report that 44 people need to be treated to prevent one infection (I got 45).

They then went on to calculate that it would cost $400,000 a year to prevent a single infection.

This figure does not even include the cost of the necessary monitoring for infection.  In another letter, it was suggested that such monitoring be done monthly to prevent the emergence of resistant virus by detecting infection early.

From Sean Strub’s calculations (in his comment to my post on the POZ magazine website) which included doctor’s visits and tests, the annual cost to prevent a single infection  would be about $500.000.

These figures are based on drug costs in the US.

Truvada PreP not only does not work well enough it will cost a half million dollars a year to prevent a single infection.

Maybe this is indeed a “game changer” but not in the sense intended by the triumphalist reports coming from the recent Rome AIDS conference.

There definitely seems to be a perception that PrEP is a viable prevention option for everybody; there even have been calls for its general implementation.  These cost estimates alone would make it unfeasible as a public health measure but there are additional reasons, importantly its relatively low efficacy.

PrEP is a reasonable option for only a very  small number of individuals at high risk for infection who are able to be regularly checked for infection.  I believe there is no disagreement about this; the controversy is only about its general use.

Implementation of PrEP on a wide scale will almost certainly result in an increase in new infections.  It’s not only adherence to the drug regimen that will not be maintained by all.  Adherence to a schedule of regular testing for infection cannot be relied on. Facilities for performing the needed tests may not even always be available.

The way PrEP has been promoted has probably already damaged targeted prevention education programs with support for continued condom use, an activity already in great need of support.

Drugs for prevention are paid for from a different budget than prevention education programs, and health departments already under budgetary constraints may feel that prevention needs can now be paid for by those entities that pay for drugs, private insurers or Medicaid/Medicare.

The amount of almost uniformly uncritical publicity given to PrEP is completely out of proportion to its utility.  It’s a hugely expensive and very poorly effective prevention intervention, of use to only a very small number of individuals, and its misleading promotion has probably already damaged prevention education programs.

Considerable resources must have been devoted to publicize and promote PrEP over many years,  in a way that has not taken care to reinforce prevention education with support for continued condom use.    One can only wonder why.

Drs Dong Heun Lee, M.D.  and Ole Vielemeyer, M.D of Drexel University College of Medicine in Philadelphia are the authors cited.