Phosphodiesterase-5 inhibitors (PDE-5 inhibitors) for erection problems


Generic Name Brand Name
sildenafil Viagra
tadalafil Cialis
vardenafil Levitra

Phosphodiesterase-5 inhibitors (PDE-5 inhibitors) are taken at least an hour before you plan to be sexually active. PDE-5 inhibitors will result in an erection only if you are sexually stimulated.

How It Works

During an erection, blood fills tissue in the penis, causing it to enlarge and become stiff. The PDE-5 inhibitors relax smooth muscle, allowing the penis to fill with blood.

Why It Is Used

PDE-5 inhibitors can be used when an erection problem (erectile dysfunction) is caused by:

  • Diabetes .
  • High blood pressure .
  • Spinal cord injury or other problems affecting nerve function.
  • Prostate surgery.
  • Side effects of medicines.
  • Emotional or psychological causes.

How Well It Works

All PDE-5 inhibitors are very effective in treating erection problems, no matter what is causing the erection problem. The three kinds of PDE-5 inhibitors (sildenafil [Viagra], tadalafil [Cialis], and vardenafil [Levitra]) have not been compared to each other in medical studies. Viagra is the oldest PDE-5 inhibitor and has been studied the most. Its side effects and long-term effects are well known. Levitra and Cialis are newer.

How well the PDE-5 inhibitors work depends on the person taking it and how much he takes. But these medicines seem to work in about 8 out of 10 men who use them for erection problems.1

PDE-5 inhibitors should be taken at least an hour before you plan to be sexually active.

One study found that tadalafil (Cialis), called "the weekend pill," enhanced the ability to have erections for 24 to 36 hours after taking it.2 Sildenafil (Viagra) and vardenafil (Levitra) usually enable a man to get an erection at any time for about 4 hours after taking it.

Sildenafil (Viagra) does not work as well as it would otherwise if you eat a high-fat meal around the time you take it, so many doctors recommend you take it on an empty stomach. Vardenafil (Levitra) may be slightly less effective if you eat a high-fat meal, but a moderate-fat meal does not reduce its effectiveness; tadalafil (Cialis) works without regard to what you eat.3

Side Effects

Do not take PDE-5 inhibitors if you are taking any medicines that contains nitrates, such as nitroglycerin. This combination can lower blood pressure dangerously, possibly leading to a stroke, a heart attack, or death. If you are taking a medicines called an alpha-blocker—used to treat high blood pressure or an enlarged prostate—check with your health professional before you take a PDE-5 medicines.

Other side effects are fairly uncommon when taking PDE-5 inhibitors. They include:

  • Headache.
  • Skin flushing.
  • Indigestion.
  • Nasal congestion.

Some men taking a PDE-5 inhibitor find that the medicine affects their vision for a few hours after they take it, usually by causing a slight bluish tinge to their vision. A few men become more sensitive to light. These effects go away in a few hours.

Some men taking PDE-5 inhibitors have had sudden hearing loss, usually only in one ear. This loss of hearing may be related to the medicine. The U.S. Food and Drug Administration (FDA) advises any man taking a PDE-5 inhibitor who has sudden hearing loss to stop taking the medicine and call a doctor immediately. The hearing loss may be reversible.

Sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) may be linked to a rare type of vision loss. If you experience sudden vision loss or vision-related problems while taking these drugs, the FDA advises you to talk to your doctor and seek medical care immediately. If you already have eye disease or vision problems (such as cataracts, glaucoma, or retinopathy), it is important for you to speak with your eye doctor (ophthalmologist) before you start taking any PDE-5 inhibitors.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Health experts have debated the use of PDE-5 inhibitors in men with heart disease, because deaths have been reported in men who used sildenafil (Viagra). The 1999 American College of Cardiology/American Heart Association (ACC/AHA) Expert Consensus Document noted that PDE-5 inhibitors may be dangerous for people who:4

  • Have coronary artery disease (CAD).
  • Have heart failure and low blood pressure.
  • Are taking many different drugs for high blood pressure.

But several studies have reported that some men with heart problems may be able to take PDE-5 inhibitors safely.

  • One study found no evidence of increased risk of heart attack or CAD in men who use sildenafil (Viagra).5
  • Another study in men with CAD reported that sildenafil (Viagra) does not lead to heart attack and that heart attacks and other cardiovascular problems reported after taking Viagra may be related more to the physical activity of intercourse than to the medicine.6
  • A study of 35 men found that sildenafil (Viagra) is safe for men with moderate heart failure.7

Sexual activity is exercise. If you have a heart condition and have not been sexually active for a while, talk with your health professional to make sure you can safely engage in sexual activity.

PDE-5 inhibitors are not prescribed for anyone who may take nitroglycerin in an emergency.

Tell your health professional if you are using PDE-5 inhibitors and are going to have a test for heart disease (such as a stress treadmill test, cardiac catheterization, stress thallium, or stress echocardiography). Do not take sildenafil (Viagra) or vardenafil (Levitra) for 24 hours before the test. Do not take tadalafil (Cialis) for at least 48 hours before the test. Then if you develop a problem during the test, it will be safe for you to use nitrate-containing medicines such as nitroglycerin.

When considering PDE-5 inhibitors for erection problems, it is important to include your partner in your discussions.

If you take any medicines, discuss PDE-5 inhibitors with your health professional before using them.

PDE-5 inhibitors can be prescribed by any doctor. You do not have to see a doctor who specializes in sexual health. PDE-5 inhibitors are also available on the Internet; if you obtain the medicine through this route, you should discuss its use with your doctor.

PDE-5 inhibitors may affect fertility. If you are trying to have a child, you may want to ask your doctor about how this medicine can affect your chances of conceiving.

Sildenafil (Viagra) costs $8 to $10 per pill, and not all insurance plans will cover the cost of the medicine. Most insurance plans that do cover Viagra will approve only a limited supply.

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  1. Lue TF, Broderick GA (2007). Evaluation and nonsurgical management of erectile dysfunction and premature ejaculation. In AJ Wein, ed., Campbell-Walsh Urology, 9th ed., vol. 1, pp. 750–787. Philadelphia: Saunders Elsevier.
  2. Porst H, et al. (2003). Efficacy of tadalafil for the treatment of erectile dysfunction at 24 and 36 hours after dosing: A randomized controlled trial. Urology, 62(1): 121–125.
  3. Seftel AD, et al. (2004). Erectile dysfunction: Etiology, evaluation, and treatment options. Medical Clinics of North America, 88(2): 387–416.
  4. Cheitlin MD, et al. (1999). Use of sildenafil (Viagra) in patients with cardiovascular disease. ACC/AHA expert consensus document. Circulation, 99(1): 168–177.
  5. Shakir SAW, et al. (2001). Cardiovascular events in users of sildenafil: Results from first phase of prescription monitoring in England. BMJ, 322(7287): 651–652.
  6. Arruda-Olson AM, et al. (2002). Cardiovascular effects of sildenafil during exercise in men with known or probable coronary artery disease. JAMA, 287(6): 719–725.
  7. Webster LJ, et al. (2004). Use of sildenafil for safe improvement of erectile function and quality of life in men with New York Heart Association classes II and III congestive heart failure. Archives of Internal Medicine, 164(5): 514–520.

Last Updated: May 21, 2008

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