Administration and Effect. PDE inhibitors work only when the man experiences some sexual arousal. They are generally effective within 30 to 120 minutes when taken on an empty stomach. Sildenafil should be taken on an empty stomach; vardenafil and tadalafil may be taken with or without food. One study suggested that crushing a Viagra tablet and letting it dissolve under the tongue may speed up its actions. Its effects may last for several hours. PDE 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. One study suggested that it should be tried at least eight times using the appropriate dose. In such cases, success rates are over 80%.
PDE5 inhibitors can also be used in combination with testosterone replacement therapy, but this combination may cause a number of side effects. A small study in the Journal of Urology found that combination therapy of sildenafil and testosterone gel may help restore sexual function in men with low testosterone levels who do not respond to sildenafil alone.
Side Effects and Other Limitations. Common side effects of PDE inhibitors include flushing, gastrointestinal distress, headache, nasal congestion, back pain, and dizziness.
Effects on the Heart. There were early reports of fatal heart attacks in a small percentage of men taking sildenafil (Viagra). Viagra can cause drops in blood pressure that can be sudden and possibly dangerous when the drug is taken with nitrate drugs, such as nitroglycerine, which are used for angina. Such effects have been fatal in some men. Other effects on the heart and blood vessels are not wholly known. For example, although some studies report improved blood flow to the heart, a 2001 study reported that the drug may excite the nerves associated with heart function. Nevertheless the most recent studies have not found a higher risk from PDE5 inhibitors for adverse heart events in men with heart disease who are not taking nitrates. In fact, some evidence suggests it may be safe for men with congestive heart failure who have the physical capacity for sexual intercourse. The bottom line is that no one taking nitrates, including the recreational drug amyl nitrate, should take sildenafil or any other PDE inhibitors. Caution is still warranted for men with severe heart disease, all evidence is reassuring on its safety for the heart.
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