Erectile dysfunction

Drug Store News, Feb 15, 1999 by Carol Dickson McKee

With sexual arousal, nitric oxide is released from nerve endings and endothelial cells, binding to smooth muscle of the corpus cavernosum and activating the enzyme guanylate cyclase, which results in increased concentrations of cGMP production. Penile erection is facilitated by cGMP, which relaxes smooth muscle and allows inflow of blood and engorgement. The conversion of cGMP to GMP reverses this process, so inhibiting conversion potentiates penile erection.

Phosphodiesterase type 5 is also found in vascular smooth muscle. Sildenafil has less effect on phosphodiesterase type 6, which is found in the retina, and phosphodiesterase type 3, which is involved in cardiac contractility.

Does sildenafil really [work.sup.14]?

The current general consensus is that sildenafil is often effective in treating erectile dysfunction. The manufacturer reports statistically significant improvement in erectile dysfunction in patients with cardiovascular disease (note drug interactions and warnings), diabetes, transurethral prostatectomy, spinal cord injury and in those taking antidepressants (note potential drug interactions), antihypertensives or antipsychotic medications.

The manufacturer reports that in clinical trials, approximately 3-out-of-4 men taking sildenafil achieved erections, compared with 1out-of-4 men taking placebo. Patients reported that about 2-out-of-3 of their attempts to have sexual intercourse were successful while taking sildenafil, compared to 1out-of-5 attempts for patients taking placebo.

What side effects can occur with [sildenafil.sup.12-18]?

At recommended doses, sildenafil tends to lower blood pressure slightly, but it may decrease blood pressure dramatically, and result in fatalities in patients who are also taking nitrates. Sildenafil is, therefore, contraindicated in patients taking any type of nitrates.

The most common side effects are headache, flushing and dyspepsia. Nasal congestion, diarrhea, dizziness and rash have also been reported. Sildenafil does not appear to cause priapism. It may cause increased sensitivity to light and blurred vision. Transient abnormal vision, usually a bluish-color tinge or, at higher doses, difficulty differentiating between blue and green, is relatively rare, but may be of special concern for some patients. The Federal Aviation Administration has, for example, recommended that pilots not take sildenafil within six hours of flying, because it may make it difficult to distinguish between the blues and greens found in cockpit instruments and runway lights.

Which drug interactions are important with [sildenafil.sup.12-20]?

Nitrates * Potentially fatal interation

Fatal reactions have occurred in patients taking sildenafil and nitrates, so sildenafil should not be used in patients taking any type of nitrates (Table 2). Patients who have taken sildenafil and who are treated by paramedics or emergency medical technicians or who present to urgent visit or the emergency department should not be given intravenous nitroglycerin or sodium nitroprusside (Nitropress(R)), a medication which is sometimes used to treat hypertensive emergencies.