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Sildenafil is a medication used to treat erectile dysfunction (ED), pulmonary arterial hypertension (PAH), and high-altitude pulmonary edema (HAPE). It works to treat these conditions by relaxing blood vessels. Side effects of the medication can include headache, dizziness, blurred vision, and low blood pressure. Patients with heart disease, liver dysfunction, or renal impairment should use caution in taking the drug because they could experience severe side effects.
The mechanism of action of sildenafil is to inhibit an enzyme called phosphodiesterase, which usually helps speed up various reactions within cells. When this enzyme is inhibited, levels of a chemical species called nitric oxide increase. This chemical helps promote the relaxation of blood vessels in different parts of the body.
The pharmaceutical company Pfizer® initially developed sildenafil to treat high blood pressure. When the drug was tested in clinical trials, some male patients reported an interesting side effect. They had an increase in the frequency and strength of penile erections. Pfizer® decided to test the drug as a treatment for ED, and eventually marketed the drug under the brand name Viagra®.
The main use of sildenafil is treat patients with erectile dysfunction. Men can take a pill containing the medication 30 minutes to four hours before the time of desired sexual intercourse. The medication works by increasing blood flow to the penis.
Another use of sildenafil is to treat patients with a condition called pulmonary arterial hypertension. People with this disease suffer from a lack of blood flow to the lungs, and develop problems with fatigue and shortness of breath. In some patients, taking the medication can increase the amount of blood the lungs receive, and they experience fewer symptoms. When used to treat PAH, the drug is prescribed under the brand name Revatio®.
Recently, some investigators have suggested that sildenafil can be effective in treating patients with high-altitude pulmonary edema, a condition that causes fluid to collect in the lungs of some people ascending to high altitudes. The disease could be considered a severe form of altitude sickness. Different researchers have used the medication to treat HAPE, and have also given the medication to prevent the development of this condition.
Side effects of sildenafil can include headache, flushing, dizziness, blurred vision, and abdominal pain. The medication should not be taken with nitrates, which are drugs used to treat chest pain, because the combination could cause a dangerous drop in blood pressure. Patients who have erections for longer than four hours should go to the emergency room because this condition could result in damage to the penis.
Although many patients are able to take sildenafil without problems, some patients are not good candidates for treatment with this medication. It should not be given to patients who have had a recent heart attack or stroke. Underlying conditions such as unusually low blood pressure, abnormal liver function, or renal impairment could increase patients' risks for severe side effects, and the drug should be used with caution in these people.