Thursday, June 02, 2005

Viagra and STD's among gay males

Mediocre science always upsets my stomach. Should this cause me to reach for the Maalox? A review article in the American Journal of Medicine examined 14 studies looking at the use of Viagra among gay males. The authors noted that sexually transmitted diseases (STD's) were more common among Viagra users than nonusers. This in itself is a somewhat provocative finding that may be of some concern.

The problem I have is that they then concluded that this finding warranted government intervention. Possibilities included warning labels and making Viagra a controlled substance (which would eliminate free samples and lower black market availablility).

I'm definitely an advocate of patient safety but before intervening in a situation like this, I'd like the science to be a bit more robust. Clearly, these researchers know the difference between cause and effect vs. association (and mention that their data cannot establish causality). The fact is that there is not enough information at present to make definitive conclusions. The studies examined are observational studies, not clinical trials.

The authors noted an association of Viagra use among gay men with:
  • Increased rate of sexually transmitted diseases
  • Practicing unprotected sex with partners of unknown or different HIV status
  • HIV positivity
  • Increased likelihood of using methamphetamine within the past four weeks

Far be it for me to dismiss these findings as unimportant but without more rigorous study, there is no way to know whether these relationships are simply manifestations of:

  • An association of risk-taking behavior among individuals predisposed to solve their impotence problems with medications such as Viagra
  • An association of a common factor that predisposes one to both increased incidence of STD's and impotence thus necessitating medications such as Viagra (eg. alcohol or personality disorders)
  • An association of HIV disease and/or methamphetamine use with impotence (again necessitating medications)
As far as I know, Viagra has not been associated with mental status or psychiatric changes (such as disinhibition) that would constitute a direct cause of some of the consequences noted above. The possible explanations I've outlined seem more plausible to me. The Viagra merely facilitates behavior we already know is risky in the same way that gasoline facilitates traffic fatalities.

The authors' overall conclusion is "The labeling for PDI's (the class of medications Viagra is in) should be modified to warn users of an increased risk of STD's, including HIV infection."

By that logic, cold showers should be made mandatory in high risk patients. That would lower the incidence of STD's even more.

5 Comments:

Blogger james gaulte said...

Is there an epidemic of unwarranted speculation and inappropriate recommendations based on case-control studies and observational data and ready access to a Sas statistical programs?

June 03, 2005 4:15 AM  
Blogger Fred said...

I wouldn't be surprised if the vast majority of those being observed aren't really sexually disfunctional to the point of needing Viagara. I am one who occasionally uses Viagra and have found many guys thinks Viagra will increase sexual function beyond what is normal. It doesn't.

I suspect, if there is an actual correlation between Viagra users and STDs, it's more because those who use it (especially those who don't really need it) are the kind of people that take other drugs, "pill takers", and are more likely to engage in risky behavior simply because that's ingrained in their personality.

June 03, 2005 6:36 AM  
Anonymous Darth Medicus said...

once again the goverment knows what is better for us then we do.

June 03, 2005 8:31 PM  
Blogger tompain said...

Great post. I read the article, and it seems to me that fred's comment is on the right track. The study acknowledges that the majority (up to 86%) of sildenafil users acquire the drug without a prescription. Taking a prescription drug (especially a vasodilator) without supervision is risk-taking behavior, so the study's population has already been filtered for positive risk-taking behavior. I think the results might be different if the sample population were limited to sildenafil users who had been diagnosed with ED prior to 1998 (or whenever Viagra hit the market). I doubt you would see much correlation with increased STDs among that population. One suggestion in the article that sounds worth investigating is the possibility that the vasodilation may make mucus membrane tissue more susceptible to infection. Sounds plausible, but then does that mean that taking amphetamines (which constrict blood vessels) reduces your risk of infection? It's all so complicated. The cold shower starts to look like the best option.

June 05, 2005 12:35 AM  
Blogger LMF said...

It all comes down to the question of how much evidence do you need before you start acting. It's unlikely that there will ever be a randomized controlled trial of sildenafil or other PDI use in high risk MSM's, so observational studies are the best you're going to get. This is generally true whenever the adverse effects of a drug have to be proven. Most often they are identified by observational data after the initial RCT's have proven efficacy.

The same stringent argument about 'association is not causation' could be applied to all observational studies and then we will never believe the results from any of them.

I think the authors' conclusions are appropriately worded and does not make any unduly tall claims. They hype it up a little in the last sentence of the discussion, but most authors do that to give their paper a little spin. They have clearly stated their limitations. Their findings are consistent with what's known about high risk sexual behavior.

Therefore to me at least, there is enough information to start acting on the strong possibility that PDI use is associated with an increased risk of STD's and HIV. The difficult question, of course, is deciding what to do. What is likely to reduce the risk of high risk sexual behavior? I don't know if there are any RCT's to support certain interventions over others.

June 07, 2005 8:45 AM  

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