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Drugs That Interact With Viagra

By Dave Dixon ; Updated August 14, 2017

Viagra, chemically known as sildenafil, is a prescription medication used for treating erectile dysfunction. Men with erectile dysfunction have inadequate blood flow to the penis, making it difficult to form and sustain an erection. Viagra relaxes the muscle around the penis, which increases blood flow. An erection becomes possible when the individual is sexually stimulated. The potential for drug interactions is high because of how Viagra works and because it is metabolized in the liver.

Nitrates

Nitrates are a class of prescription medications indicated for the treatment of chest pain or angina in people with heart disease. Examples of nitrates include isosorbide dinitrate, isosorbide mononitrate and nitroglycerin. These medications cause blood vessel dilation similar to Viagra. Concomitant use of Viagra and nitrates may cause an unsafe drop in blood pressure. The use of blood pressure lowering medications further increases this risk. Symptoms include dizziness, lightheadedness, fainting and even heart attack or stroke in some cases. For these reasons, it is contraindicated for people on nitrates to take Viagra.

Macrolide Antibiotics

Macrolides are a class of antibiotics used to treat a variety of infections. Examples of macrolide antibiotics are erythromycin, clarithromycin and azithromycin. Macrolides inhibit the enzyme primarily responsible for metabolizing Viagra, resulting in increased concentrations of Viagra in the blood. Limit the Viagra dose to 25mg while on a macrolide antibiotic, or avoid taking Viagra until the antibiotic course is finished. In most cases, there are alternative antibiotics that are equally effective and do not interact with Viagra. Symptoms of excess Viagra levels in the blood include an erection lasting more than four hours, visual disturbances, chest pain or temporary loss of consciousness.

Protease Inhibitors

Protease inhibitors are antivirals used to treat human immunodeficiency virus or HIV. Viagra is generally contraindicated for use in patients taking protease inhibitors. The total dose of Viagra cannot exceed 25mg in a 48-hour period if Viagra is used while taking a protease inhibitor. Protease inhibitors increase Viagra blood levels potentially causing erections lasting more than four hours, visual disturbances, chest pain or temporary loss of consciousness. Consult with the physician prescribing the protease inhibitor before taking Viagra.

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