Sildenafil is a prescription medication manufactured by Pfizer. It is available as Viagra and Revatio. Sildenafil is a phosphdiesterase-5 (PDE-5) inhibitor, used primarily to treat erectile dysfunction (ED). Other PDE-5 inhibitors include the prescription medications tadalafil and vardenafil. All PDE-5 inhibitors have similar side effects—headache, flushing, upset stomach, dizziness and back pain. They should only be used cautiously if you have kidney or liver problems. If you take a nitrate or alpha-blocker for high blood pressure, any of the PDE-5 inhibitors can cause a sudden drop in blood pressure.
Viagra, or sildenafil citrate, is an oral therapy for erectile dysfunction. ED is a common medical condition, affecting about 52 percent of men between the ages of 40 and 70 years. Viagra is a blue, diamond-shaped tablet. It comes in doses of 25 mg, 50 mg and 100 mg, to be taken up to once daily. The usual recommended dose is 50 mg, to be taken one hour before sexual activity. You should not take Viagra if sexual activity is inadvisable due to an underlying cardiovascular condition. There are potential drug interactions with nitrates, alpha-blockers, anti-hypertensives, cimetidine, erythromycin and other CYP3a4 inhibitors and protease inhibitors.
Sildenafil citrate is also available as Revatio, for the treatment of pulmonary arterial hypertension (PAH). According to the FDA, PAH is a rare, aggressive disease that left untreated has an average survival of less than three years. Symptoms of PAH include fatigue, difficulty breathing on exertion, dizziness, peripheral edema and abdominal distension. Revatio is used to improve exercise ability and to slow progression of PAH. It is usually taken orally, 20 mg three times a day spaced four to six hours apart. It is a white, round tablet. Revatio is also available in an injectable formulation. The dose is 10 mg three times per day as a bolus IV injection.
Other PDE-5 Inhibitors
Two other PDE-5 inhibitors are available for the treatment of ED. Tadalafil (Cialis) is manufactured by Eli Lilly. Two formulations of Cialis are available. It can be taken "as needed" at doses of 5, 10 or 20 mg, used up to once a day. Or the "Once Daily" formulation at 2.5 or 5 mg. "Once Daily" is intended for men who anticipate sexual activity two or more times per week. It is effective for up to 36 hours.
Vardenafil hydrochloride is produced by GSK/Schering. Two forms are available. Levitra is taken orally at a dose of 2.5, 5, 10, or 20 mg. The usual starting dose is 10 mg. It should not be taken more than once a day. Staxyn, new in 2010, is an orally disintegrating tablet. The dose is 10 mg, taken 60 minutes before sexual activity, up to once per day.
Illegal Drugs with PDE-5 Inhibitors
Many dietary supplements are marketed as natural treatments for erectile dysfunction, or to enhance sexual performance. After conducting a chemical analysis, the FDA found that several of them contained PDE-5 inhibitors—like sildenafil, tadalafil or vardenafil—that were not listed on the label. The FDA warns you not to take Zimaxx, Libidus, Neophase, Nasutra, Vigor-25, Actra-Rx or 4EVERON. Though marketed online, they are in fact illegal drugs. They have not been approved by the FDA and there is no guarantee of their safety, effectiveness or purity. These supplements may be especially dangerous if you take nitrates, alpha-blockers or other anti-hypertensive medications. Your blood pressure could suddenly drop to an unsafe level and you could feel dizzy, faint or even have a heart attack or stroke.