Tuesday, June 07, 2005

More on Viagra and STD's

I wanted to respond to a comment by LMF on my Viagra and STD's post. My post discussed the data that some researchers examined and from which concluded that Viagra use led to sexually transmitted diseases (STD's). They further concluded that FDA intervention is required because of this. Unlike myself, LMF agrees with the notion of such intervention in this setting.

LMF points out that yes, observational studies don't prove causality but that at times, depending on the clinical situation, their resulting data will be the best that we are likely to get. Certainly, I can't disagree with that. I have no problem with LMF's description of the utility of observational studies. Even the authors recognized that such studies in this instance couldn't confirm causality (as I noted in my post).

Public policy frequently has to be made on the basis of imperfect knowledge. However, I don't believe that the data presented in this instance was strong enough to warrant a substantial policy change.

When strong alternative explanations for the results they reported exist that do NOT invoke causality of Viagra with sexually transmitted diseases (STD's) or high risk sexual behavior, caution is indicated.

One may reasonably disagree with my analysis of the available data but that analysis formed my opinion. This being the case, it follows that in my opinion, creating policy changes such as putting warning labels on Viagra and designating it a "controlled substance" is unwarranted. Such actions are likely to reduce the willingness of some patients who might benefit from Viagra to take it. They will also reduce the willingness of many physicians to prescribe it again to many patients that may benefit. To me, this constitutes a risk that attenuates the potential benefit to society that such a policy may yield.

I don't believe that such risk is justifiable in this case. Drugs such as Viagra are extremely useful medications by virtue of their efficacy and safety (probably more so than most drugs on the market). Any policy that will limit the availability of such an effective medication could have adverse public health consequences.

Don't laugh. Erectile dysfunction is a serious problem that few would deny interferes with many men and their partners' enjoyment of life. Isn't the alleviation of such obstacles to happiness what public wellness is or should be about?

I'm all in favor of lowering the incidence of STD's and HIV infection. If there were better data (even better observational or case-control data) to demonstrate that Viagra and drugs in its class caused such public health problems, I would definitely rethink my position. What I attempted to show in my post on the subject was that at present, I think the alternative explanations are simply too plausible to justify any interventions that would limit the availability of Viagra.

5 Comments:

Blogger tompain said...

Medicine Man

Glad you brought this up again. I agree with you completely. Alternative (behavioral) explanations for the higher incidence of STDs are not just plausible, they are more plausible than the only physiological explanation I have seen offered (that vasodilation makes mucus membrane tissue more susceptible to infection). The study clearly did not adequately cull from its population those who take sildenafil for recreational purposes, and who I believe studies would show are much more likely to engage in sex with multiple partners, which in turn would inevitably lead to a higher rate of STD infection. Acquiring and taking a prescription drug without a prescription is clearly risky, so the study's population was abnormally weighted toward positive risk-taking behavior.

I'm not for restricting Viagra. I'm for responsible science. If a legitimate study shows a danger in Viagra that does not actually arise from behavior related to recreational Viagra use, then let's start thinking about warning labels. Otherwise we might as well get right to the point and put the warning label directly on the penis.

tompain

June 07, 2005 12:16 PM  
Blogger tompain said...

And to LMF,

You wrote:

"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."

What was wrong with my earlier suggestion (in response to the initial post) that the researchers limit their study population to men diagnosed with ED prior to 1998 (or whenever Viagra hit the market)? This would probably eliminate those who use sildenafil recreationally and acquire it illegally, as well as those who obtain prescriptions by lying to their doctors.

tompain

June 07, 2005 12:26 PM  
Anonymous Anonymous said...

Isn't it difficult to get an STD if you can't have sex. So what do you know ,with viagra they can have unprotected sex. Is the STD caused by the viagra or the users stupidity. Maybe the warning should say not for use by stupid men.

June 07, 2005 7:00 PM  
Blogger LMF said...

California medicine man,
Thanks for your lucid reply to my comment. I don't know the overall literature behind this whole field of PDI's, risky behavior and STD's, so I'll take your word for it that there are enough plausible alternative explanations to justify not instituting policy changes, especially if there are the downsides of such a policy change, as you described.

Some of the studies cited in the review performed multivariate analysis. Others provided odds ratios and adjusted odds ratios, so it is likely that they did some multivariate analyses as well. However, I do not know if they included all the confounding variables necessary to cleanly isolate the association of sildenafil and STD's.

June 11, 2005 10:58 AM  
Blogger LMF said...

Tompain,
I suppose that the researchers might limit their study population to men with ED in a pre-Viagra era, but I see two problems with this: (1) The study we are discussing was a review / summary of multiple other studies, though it did not include a meta-analysis. So re-analyzing the data would be impossible, unless they contacted all the original authors and sought individual patient data from them. (2) If the hypothesis is that viagra use leads to STD's, wouldn't we need a group of men who used viagra to compare them to a group of non-users?

June 11, 2005 11:06 AM  

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