Viagra, the branded product of sildenafil, is prescription medication classified as a phosphodiesterase-5 enzyme inhibitor. It used for the treatment of erectile dysfunction. The medication does not directly cause an erection and the patient requires sexual stimulation.
Dosage
The recommended dose is 25 to 50 mg taken about one hour before sexual activity. According to the "Drug Information Handbook," the medication may be taken anywhere from 30 minutes to four hours before sexual activity.
Actions of Viagra
Viagra inhibits the phosphodiesterase-5 enzyme, which results in the relaxation in the muscles of the penis and allows the inflow of blood; this will lead to an erection.
Side Effects
Headache is one of the most common side effects occurring in up to 46 percent of patients. Facial flushing, abdominal pain, nasal congestion and dizziness are common side effects, as well. "Pharmacotherapy: A Pathophysiologic Approach" states that up to 10 percent pf patients can experience an increased sensitivity to light, blurred vision or loss of blue-green color discrimination.
Drug Interactions
Viagra increases the effect of nitrates, such as nitroglycerin or isosorbide mononitrate and is contraindicated in those patients. Other medications that may interact with Viagra include phenytoin, diclofenac, azole antifungals and carbamazepine.
Warnings
Patients who have or are currently on medications that lower blood pressure should use Viagra with caution. Physicians should also use caution in patients with cardiovascular disease, peptic ulcer disease or bleeding disorders.
References
- "Drug Information Handbook"; Charles F. Lacy, Lora L. Armstrong, et al.; 2007
- "Pharmacotherapy: A Pathophysiologic Approach"; Josep T. Dipiro, Robert L. Talbert., et al.; 2008
