update on viagra

by director Chris Steidle, MD

Viagra is the first orally administered phosphodiesterase (PDE) inhibitor and was approved by the Food and Drug Administration in 1998 as the first truly effective oral medication for the treatment of erectile dysfunction.

In the short time since its approval, Viagra has literally become a household word.

It is one of the fastest growing drugs in terms of sales and it has set many records for the number of prescriptions written. At the same time, it has spawned a host of urban legends. As a matter of fact, the mystique surrounding Viagra includes stories about women who have been attacked by sex-crazed husbands taking the drug and about men that have had heart attacks as a nasty side effect.

This article is to review what is currently known about Viagra, including its safety record and appropriate warnings about taking it. However, your physician is the best person to advise you about whether a drug is right for you based on your own medical history and current condition.

At first, Viagra was simply a byproduct of pharmaceutical experiments and was initially used as a treatment for high blood pressure. In its early tests as a hypotensive drug among young, male, medical students, it produced what is called an adverse event, an erection.

Researchers worked to determine the ingredient that caused this surprise effect and Viagra was reborn.

The science surrounding the discovery of Viagra has dramatically improved our understanding of the process that leads to erections. We know that the smooth muscle in the human penis, the cylinder called the corpus cavernosum, contains compounds called PDE receptors, and specifically, the type-5 receptor, which is responsible for creating the erection. In brief, nitric oxide is released from nerves within the corpus cavernosum during sexual stimulation, which activates an enzyme called guanylate cyclasa. This enzyme helps elevate the level of cyclic guanosine monophosphate (cGMP), which, in turn, acts to relax the cavernosum tissue and an erection occurs. By inhibiting the breakdown of the cGMP, ingredients in Viagra induce and enhance the relaxation of the corporeal smooth muscle. In other words, Viagra prevents the breakdown of a compound that produces an erection, thereby prolonging it and even stimulating its occurrence in men who would not have a strong erection otherwise.

When taken orally, Viagra is rapidly absorbed and maximum concentrations are seen within one hour after taking the pill, provided it has been taken several hours after a meal. Its half-life, the speed with which the drug is broken down by the body, is roughly three to five hours. I usually recommend that my patients try Viagra before trying any other treatments for erectile dysfunction. When a man fails to get a good response from Viagra, it’s time to try other treatment regimens.

Viagra is taken one hour before anticipated sexual activity and on an empty stomach. Eating a high fat meal just prior to taking Viagra can greatly decrease its effectiveness. The most important contraindication (and really the only major one) for Viagra is when a patient is also taking nitroglycerin. Taking nitrates in conjunction with Viagra greatly enhances the hypotensive or low blood pressure effect and can cause death. Taking doses greater than 100mg does not provide additional erectile benefits and may increase the amount of side effects. I usually tell patients to use the lowest effective dose, which is both a cost effective way to use the drug as well as a way to decrease side effects.

The vast majority of men taking Viagra do not have problems with side effects. The most common side effects reported include headaches, a flushing phenomenon of the face, and trouble with dyspepsia or acid reflux. Additionally, some men complain of nasal congestion. Only 1.2 percent of patients who took Viagra in the confines of a controlled study stopped the medication due to side effects. Visual side effects have been misrepresented in the press and consist basically of a blue haze seen at higher doses. This effect occurs because phosphodiesterase, and used PDE receptors, are also present in the retina.

Originally, it was thought that Viagra produced an erection that lasted too long, a painful condition known as priapism. This condition was never reported during the clinical trials and has been seen very rarely in post-marketing follow up data. The chance of this effect occurring is extremely low. However, if a man’s erection lasts for more than 4 hours, he should seek medical help immediately, as this condition can permanently damage the penis.

Approximately seventy percent of men respond positively to Viagra and it is effective in patients with either organic or psychogenic erectile dysfunction. If Viagra doesn’t produce dramatic results, I tend to look for what else is going on. I check to see if the problem might be caused by poor absorption as a result of not taking the medicine on an empty stomach or the patient may have one of several conditions interfering with erections. These include diabetes and the effects of radical prostate surgery, both of which may significantly reduce the efficacy of Viagra. Overall, Viagra is very safe and effective and as long as a physician monitors its use, there should be no worries about using it.

References

Steidle, CP. The Impotence Sourcebook. Lowell House. 1998.

Posted January 2002
Last updated April 2003