Oral Medications (PDE5 Inhibitors):

Three medicines taken by mouth are approved for the treatment of erectile dysfunction:

• Sildenafil (Viagra)
• Vardenafil (Levitra)
• Tadalafil (Cialis)

These drugs all work equally well. All three are known as phosphodiesterase-5 (PDE5) inhibitors. By blocking the PDE-5 enzyme, these drugs help the smooth muscles of the penis to relax and increase blood flow.

PDE5 inhibitors are generally the first choice of treatment for erectile dysfunction.

Candidates for PDE5 Inhibitors

PDE5 inhibitors are a good choice for men at any age who are in good health and who do not have conditions that preclude taking them.

However, PDE5 inhibitors are not suitable for everyone. Men who take nitrate drugs for angina, or certain types of alpha-blockers for high blood pressure and benign prostatic hyperplasia, should not take PDE5 inhibitors. The PDE5 inhibitors are less effective in men with diabetes and in men who have been treated for prostate cancer.

Men with the following conditions should not take PDE5 inhibitors without the recommendation of their doctors and even then should use them with caution:

• Severe heart disease, such as unstable angina, a recent heart attack, or arrhythmias. Men with heart disease may benefit from an exercise test to determine whether resuming sexual activity increases their risk of a heart attack.
• Recent history of stroke
• Hypotension (very low blood pressure)
• Uncontrolled hypertension (high blood pressure)
• Uncontrolled diabetes
• Severe heart failure
• Retinitis pigmentosa. (With this genetic disease, people do not produce phosphodiesterase-5 and do not respond to PDE5 inhibitors.)

Administration and Effect

PDE5 inhibitors work only when the man experiences some sexual arousal. They are generally effective within 15 - 45 minutes. Sildenafil should be taken on an empty stomach; vardenafil and tadalafil may be taken with or without food. The effects of these drugs may last for several hours, and tadalafil may last for up to 36 hours. PDE5 inhibitors should not be used more than once a day.

Success rates increase with the number of attempts, so a man should not be discouraged if the drug does not work at first.

PDE5 inhibitors can also be used in combination with testosterone replacement therapy for men with hypogonadism (low testosterone levels).

Side Effects

Common side effects of PDE inhibitors include flushing, upset stomach, headache, nasal congestion, back pain, and dizziness.

Effects on the Heart. There have been reports of fatal heart attacks in a small percentage of men taking sildenafil (Viagra). Viagra can cause sudden and dangerous drops in blood pressure when the drug is taken with nitrate drugs, such as nitroglycerine, which are used for angina. No one taking nitrates, including amyl nitrate, should take sildenafil or any other PDE5 inhibitors.

Intercourse itself involves an increase in physical exertion and a small risk of heart attack for patients with known heart disease or those at risk.

Visual Effects. About 2.5% of men who take these drugs develop vision problems that include seeing a blue haze, temporary increased brightness, and even temporary vision loss in a few cases. The effect is usually temporary, lasting a few minutes to several hours. Men at risk for eye problems who take PDE5 inhibitors regularly should have frequent eye examinations with an ophthalmologist. Men should also see an eye doctor if visual problems last more than a few hours.

In a few cases, these drugs have been associated with partial vision loss. The vision loss was caused by non-arteritic anterior ischemic optic neuropathy (NAION), a condition that occurs from poor blood flow to optic nerves. However, doctors note that erectile dysfunction is itself linked to the same vascular problems that cause NAION. Patients who suffer from diabetes, high blood pressure, and heart disease are at higher risk for erectile dysfunction as well as other vascular problems such as NAION. Information concerning vision loss has been added to the labels of these drugs, but the risk of blindness appears small. Still, patients who use this medication and experience a sudden loss of vision should immediately stop taking the drug and contact their doctor.

Hearing Loss. A small number of men have experienced sudden hearing loss in one ear, sometimes accompanied by ringing in the ears and dizziness. If you have this symptom, immediately contact your doctor.

Seizures. There have been a few reports of seizures in men taking sildenafil. These are rare occurrences and it is not clear if there is any causal association.

Risk of Priapism. PDE5 inhibitors pose a very low risk for priapism in most men. (Priapism is sustained, painful, and unwanted erection.) Exceptions are young men with normal erectile function.

Interactions with Other Drugs. In addition to serious interactions with nitrates, PDE5 inhibitors may also interact with certain antibiotics, (such as erythromycin), and acid blockers, such as cimetidine (Tagamet). Patients should tell their doctor about any other medications they are taking.