Posted on December 12th, 2010 No comments
Pre-Exposure prophylaxis - PrEP - iPrEx trial results.
Pre-exposure prophylaxis, or PrEP, is an HIV prevention intervention in which anti-HIV drugs are taken to prevent infection. A safe, effective and affordable drug that could achieve this would be a powerful prevention intervention even possibly capable of halting the spread of the epidemic.
Last week we were told the results of the iPrEx trial that tested the efficacy of PrEP with Truvada, a combination of two anti-HIV drugs, in reducing new HIV infections among a group of men who have sex with men considered to be at high risk for HIV infection.
The announcement of the results was greeted with almost universal jubilation.
“That’s huge,” said a prominent AIDS researcher, “That says it all for me.”
“Today marks a major step forward in our quest to combat HIV among MSM
“This discovery alters the HIV prevention landscape forever,”
“….. the new data “represents the most promising development in HIV/AIDS since the introduction of triple combination drug therapy in 1996.”
“This is a game-changing trial result,”
Science magazine reported that..
“The researchers applauded and some even cried when they heard the bottom line”; “I have not cried this hard in years” – said one researcher.
These exultant cheers are usually reserved for the most momentous of breakthroughs.
Demonstrating that a drug could be safe and effective in preventing infection would indeed be a momentous breakthrough as already noted.
But the iPrEx results, far from representing such a breakthrough, indicated that PrEP, at least with Truvada, together with counselling and provision of condoms, reduced new HIV infections among men who have sex with men only modestly. It’s unlikely that the 44% reduction in new infections that was seen is of sufficient magnitude to make PrEP with Truvada viable as a public health prevention intervention. Moreover, as will be described there are significant safety concerns, a demonstrated danger of the emergence of drug resistant HIV, and the drug is far from affordable.
A 44% reduction in new infections is not huge; even those extolling the trial results would agree (at least I think they would, but who knows considering the over-the-top responses).
But what is most troubling is that the researchers have squeezed an efficacy of Truvada of over 90% by a questionable statistical sleight of hand, an improper use of sub-group analysis, a technique of data dredging has been soundly discredited. I’ll return to this.
This has resulted in headlines such as “PrEP works – if you take your pills”, I don’t know if this will persuade some people to abandon condoms and religiously take their pills. Unfortunately the type of analysis that provides confidence to do so is not reliable. Maybe consistent use of Truvada will reduce new infections by over 90%. Maybe not.
For the moment staying with the ability to reduce new infections by 44%, as a public health intervention to be used on a wide scale, this degree of efficacy is just not good enough to justify using Truvada to prevent a life threatening infection. Even if the risk of infection is low this must be balanced against the gravity of the infection. About 3% of participants in the Truvada arm of the trial became infected as opposed to about 5% among those receiving placebo.
Perhaps it’s on this issue that I’m at odds with the huge acclaim given to the trial results. Maybe the prevailing view is that a 44% reduction in new infections is indeed good enough; some commentators are even discussing implementation.
PreP proponents like to compare it to malaria prophylaxis. If the efficacy of malaria prophylaxis were of the same order as that of Truvada in relation to HIV, I suspect many people might think twice before visiting an area where there was a risk of malaria.
Let’s take a closer look at the trial results, particularly the claimed greater degree of efficacy in compliant participants reported in the New England Journal of medicine.
I have commented briefly on this in my blog on the POZ magazine website.
The medication used in the trial, Truvada, is a combination of two HIV anti-HIV drugs, FTC and tenofovir. It was compared with placebo in over 2000 men who have sex with men, considered to be at high risk for HIV infection.
The 44% reduction in new infections was achieved in conjunction with counselling, provision of condoms and monthly tests to monitor for infection.
This is not a good enough performance to justify widespread use of Truvada to protect against infection. The investigators then looked at blood and tissue levels of the drugs in people who became infected and those who did not. They found that those who remained uninfected had detectable drug levels while those who became infected did not.
They incautiously trumpeted this result as proving that Truvada works well if the pills are taken consistently – stating that in those who took their pills more consistently the relative risk reduction was well over 90%.
On the surface this sounds good. Almost all the commentators thought so.
However looking at the results in a sub-group of participants can be misleading. Most particularly in a sub-group that is defined after randomization; who would or would not comply with treatment could not have been known. The problems with subgroup analyses will be clearer after a short account of intention to treat analysis.
Intention to treat analysis is the most reliable way to analyse clinical trial data. In such an analysis participants are analysed in the group to which they were randomized, irrespective of whether they dropped out, or didn’t adhere to the treatment or strayed from the protocol in other ways. This seems counter-intuitive, but there are sound reasons why intention to treat is regarded as the best way to analyse trial data, among them that it more reliably reflects what happens in real life, rather than in a clinical trial. For example, one reason why pills may not work is because they are not taken. If they are not taken in a trial we have to be concerned that they may not be taken in real life. Take a look at this excellent explanation of intention to treat: Making sense of intention to treat.
As noted, the trial investigators made a lot of the sub-group analysis showing greater efficacy in those who took Truvada pills as measured by finding the drugs in blood and tissue samples.
This is surprising as the pitfalls inherent in such post-hoc sub-group analyses have been recognized for years. Commentators, some of whom are clinical researchers, in their over-the-top exultation at the results of the analysis in those compliant with Truvada may have forgotten about the treachery inherent in sub group analysis. A few commentators give the problem only passing acknowledgement.
This is a classic paper on sub group analysis:
Yusuf S, Wittes J, Probstfield J, Tyroler HA: Analysis and interpretation of treatment effects in subgroups of patients in randomized clinical trials.
Journal of the American Medical Association 1991 , 266:93-98
This is from that paper:
“Analysis of improper subgroups, though seductive, can be extremely misleading, because a particular treatment effect may influence classification to the subgroup. Thus, an apparent subgroup effect may not be a true effect of treatment but rather the result of inherent characteristics of patients that led to a particular response or to the development of side effects”.
In iPrEx the subgroups were categorized by events that happened after randomization, so the adherent group is an “improper” subgroup. “Subgroups of clinical trial subjects identified by baseline characteristics … is a proper subgroup while a subgroup determined by post randomization events or measures is an improper subgroup”.
In actuality the attention given to the subgroup that had blood and tissue drug levels is an example of the treachery of such sub-group analyses.
As an illustration, the reduction in new infections seen in this group may well have resulted from the following possibility.
People who take their pills consistently are more likely to use condoms consistently and in general are more attentive to risk. So if it were possible to do a subgroup analysis of people who adhered to placebo we might conclude that the placebo also works – (and it’s cheaper).
This is not so fanciful.
“In one study , those who adhered to the trial drug (clofibrate) had reduced
mortality; but those who adhered to the placebo pill had the same reduction in mortality”.
This is from:
Coronary Drug Project Research Group. Influence of adherence to treatment
and response of cholesterol on mortality in the coronary drug
project. Engl J Med 1980;303:1038-1041
A classic example of the pitfalls of subgroup analysis is what it demonstrated in the ISIS-2, a trial examining the effects of aspirin after myocardial infarction. A subgroup analysis showed it was of benefit to all except in people who were either Libras or Geminis.
Maybe Truvada taken consistently can reduce new infections by over 90%; maybe not. There was no basis for the investigators and commentators to present the first possibility with such overwhelming confidence.
We must accept that a 44% reduction in new infections is at this time the most reliable estimate of Truvada’s efficacy as PrEP. Although, the confidence interval , a measure of reliability, was wide.
We have an intervention that can reduce new infections by 44%, if taken in conjunction with a program of counselling, condom use, and monthly tests for HIV infection. That is the benefit. What about the down side?
The two most important are the development of resistance of HIV to the component drugs of Truvada and the toxicity of the drugs.
The utility in treating HIV infection of FTC and tenofovir – Truvada’s component drugs is lost if the virus becomes resistant to the drugs. Moreover, some mutations conferring resistance to these drugs can also affect sensitivity to some other drugs. The danger of resistance, and even cross resistance to other drugs developing when Truvada is used as PrEP is not a trivial concern. Truvada used as PrEP provides a suboptimal dose in treating established HIV infections. This is precisely the situation in which resistance is likely to develop. There were in fact two instances of developed resistance in the iPrEx trial in individuals who became infected, but undetected before the trial began.
Resistant viruses in the community are a danger to all, so the risk of generating resistance is not confined to the individual taking Truvada as PrEP.
What about safety?
The claim in many reports that Truvada is without significant toxicity is also misleading.
Maybe poor adherence has some bearing on the lack of significant toxicity.
A median of 1.2 years exposure to Truvada can tell us little about cumulative and long term effects. Experience with long term use of Truvada in HIV infected people makes concern about toxicity realistic. Renal toxicity, sometimes severe occurs not uncommonly. It’s mostly but not always reversible on stopping the drug. Thinning of bones, osteopenia and osteoporosis is also seen. There are additional adverse effects associated with the drugs.
There were small abnormalities in some paramaters measuring kidney function among those treated with Truvada. Although these changes were reversible on stopping the drug, the fact that they were seen at all is a reason for great concern about the effects of longer term treatment.
With the experience we have gained from longer term treatment with Truvada, it is disingenuous to stress its overall safety from just 1.2 years of very inconsistent use.
It’s important to point out that for HIV infected individuals, the benefits of treatment with Truvada far outweigh the risks. For uninfected individuals, an entirely different risk benefit analysis must be made.
Despite the disappointing results of iPrEx, PrEP is important.
Why is PrEP important?
There are at least two important reasons.
PrEP could protect receptive partners in sexual intercourse, both men and women, who are unable to ensure that a condom is used by their partner and for a variety of reasons are unable to refuse sex . The best and most respectful way of addressing this would be to find ways to empower these individuals; in some way providing them with the means to protect themselves could be seen to also have the effect of perpetuating their subjugation and abuse.
But there are women and men who need protection now and providing them with a means to prevent infection that they can control is vital. This can go hand in hand with working to empower them and helping them to try to ameliorate or leave abusive relationships.
Sex is one of life’s joys. It is vitally important to the human experience.
Condoms can be a barrier to intimacy which for many is the most essential aspect of sexual intercourse, for both receptive and insertive partners. So recommending the use of condoms without acknowledging the significant obstacle they may present to a fulfilling sexual experience is a real problem. Pleasure is part of that fulfilment and for some insertive partners condoms are a significant impediment to experiencing it.
A fully effective and safe means of pre-exposure prophylaxis may also allow the removal of a barrier to conception.
But people are different; for example some individuals have found that condoms can increase intimacy in the reassurance they provide concerning their and their partners safety.
We should never minimize or trivialize the difficulties condoms can present. We should also keep in mind that their use is the most effective means of preventing sexual transmission of HIV.
Their use will remain necessary in order to remain uninfected until we are free from HIV or a safe an effective PrEP method can be found.
These considerations, a prevention method that the receptive partner can control,allow conception and remove an impediment to full sexual expression are reasons to work towards finding a safe and effective form of PrEP. If this can be achieved safely and affordably it could even help to bring the epidemic to an end.
Truvada unfortunately has not proved to be sufficiently effective or safe to be of utility as a general recommendation. The use of condoms still remains the most efficient way to prevent the sexual transmission of HIV.
A few words about prevention education and condoms:
The consistent use of condoms is the most effective means to prevent sexual transmission of HIV.
PrEP proponents agree but many go on to say that people just don’t use condoms consistently. This is an attitude that has apparently concluded that prevention education does not and cannot work.
But how can one conclude that it does not work when there has been so little of it? This has some analogy with the claims made for the efficacy of Truvada. It works, if you take the pills
If prevention education has been a failure, it’s not because it doesn’t work, but because we have not provided it well enough. There has been too little and most has not been properly targeted.
Proper targeting to those most at risk is critical. I have written about this. We need more and better prevention education.
The CDC now tells us that the group at greatest risk by far in the US is men who have sex with men. Nothing has changed except the ethnic distribution, so why are they only telling this to us now? For over twenty years we were told that AIDS was an equal opportunity infection making prevention education targeted to those at greatest risk even more difficult.
It’s only now, 25 years too late, that the CDC appears to recognize the urgency of providing prevention education to gay men.
Neglect of properly targeted prevention education, with encouragement for condom use and continuing support to sustain their use helped to allow the spread of HIV into African American communities in plain view while millions were spent on “America Responds to AIDS” a vacuous prevention message.
Similarly we have known for years that in the US younger men who have sex with men are at particular risk. We know where to target prevention messages, but we don’t do it well enough.
We know that highly targeted prevention education, when crafted by the communities at greatest risk can work. This was demonstrated in the earliest years of the epidemic in San Francisco and New York City.
In 1982 when Michael Callen, Richard Berkowitz and I first recommended condom use to gay men in New York City, we stressed that in doing so it was important to celebrate sex, recognizing that for some individuals condom use, or perhaps more precisely, HIV, could present a barrier to its full expression. We have come far in freeing ourselves from long standing societal constraints that for too many have stood in the way of a fulfilling sexual experience burdening it instead with guilt. It’s important to take care in providing continuing support for condom use and recognize that for many they do get in the way. But it’s really HIV that’s getting in the way, and consistent condom use can help to bring it to an end.
Finding conditions where sex without condoms is safe is important. On the showing of iPrEx – despite its ecstatic reception, PrEP unfortunately is not yet ready.
At the moment consistent condom use is the best protection there is.
The often uncritical response to iPrEx should not persuade anyone that Truvada is a safe and effective alternative.
iPrEx is a large and complicated study. The investigators deserve the highest praise for completing this difficult phase and for havine provided a result. It may not be the result that many had hoped for. But providing clear information is a great achievement and a major advance . iPrEx results clearly show that continued condom use is still necessary to prevent the sexual transmission of HIV.