In March 1998, the FDA approved Viagra for clinical use after several years of supervised drug trials on 1,500 men. Further trials bring the total research experience to over 3,000 men. In the first six months after the drug's release, the Center for Sexual Function at Lahey Hospital & Medical Center evaluated 714 men using the Viagra.
Viagra increases the activity of a chemical in the penis called nitric oxide, which creates erections. This action must coincide with sexual activity (foreplay is needed). The maximum blood levels occur in 60 minutes. Sexual activity should start from 30 minutes to six hours after taking the pill. A high-fat meal will decrease the amount of medication absorbed into the blood, thus decreasing the effectiveness. Viagra works better if taken one hour before or two and a half hours after eating.
Viagra comes in 25-mg, 50-mg and 100-mg tablets. The typical starting dose is 50 mgs. For patients who have liver disease, kidney disease or who take certain medications, 25 mgs is used. If the starting dosage does not work after several attempts and there are no side effects experienced, the dosage can be increased, but only up to 100 mgs, as the incidence of side effects goes up with the increase in dosage.
Patients who take nitroglycerin or who have it at home as either tablets or patches should not take Viagra, as the combination may cause a marked lowering of blood pressure. Patients with low blood pressure may put themselves at even greater risk. Other medications may increase the side effects of Viagra, and even some commonly used medications–such as cimetidine (Tagamet) or erythromycin tablets that treat fungal infections–may also cause problems. A careful risk history should be taken before Viagra is dispensed. In 400 apparently Viagra-related deaths reviewed by the FDA, it was discovered that some patients died from combining Viagra with nitroglycerin while most of the others died as a result of expending energy on sexual intercourse. Very few died as a result of the Viagra itself. Patients on alpha-blockers (e.g., Hytrin, Cardura, Flomax) for an enlarged prostate should not take the two drugs within four to six hours of each other. Side effects of Viagra have been mild in most patients involved with clinical trials. Long-term effects of the drug are not known. Common side effects are headache, hot flashes or facial reddening (70 percent), acid indigestion or regurgitation, and nasal congestion (7.3 percent). Less commonly, there can be sensitivity to light or distortion of blue-green color discrimination. The success of Viagra in our experience has been good–almost 82 percent higher than that stated in research trials. We feel that this is because other medical issues are addressed concurrently. Viagra works quite well, even in men with performance anxiety. There are some categories of medical conditions that have poorer results, due to nerve damage as a result of diabetic neuropathy or from prostate surgery. Approximately 9 percent of the patients we've seen have conditions that might put them at risk for complications. Interestingly, about 15 percent of patients preferred to consider other treatment modalities due to a fear of side effects from this new category of medications. In our early experience evaluating more than 700 patients, no serious problems were encountered. Viagra is not indicated as an enhancer in men with normal sexual function.
Lahey's Center for Sexual Function participated in the first female clinical study with Viagra. Results indicated that the drug may not help with libido problems, but it may enhance lubrication in orgasmic response. Viagra may be given off label, as long as women understand that it is not officially approved (so insurance won't pay for it) and safety data is limited.