Viagra (sildenafil)

VIAGRA (sildenafil) – a phosphidiesterase-5 (PDE-5) inhibitor drug commonly used to treat erectile dysfunction in men. The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum.

FDA approved uses: Viagra is indicated as for the treatment of erectile dysfunction.

Available dosage forms: Tablets – 25, 50, 100 mg.

Usual dosage: The recommended initial dose is 50 mg taken, as needed, approximately 1 hour before sexual activity. However, Viagra may be taken anywhere from 4 hours to 0.5 hour before sexual activity. Based on effectiveness and toleration, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. Maximum frequency is once per day.

Contraindications: Patients with known hypersensitivity to sildenafil or to any excipients used in the formulation. Viagra is contraindicated in patients using organic nitrates (e.g. nitroglycerine) either regularly or intermittently in any form.

Special warnings: Severe hypotension and death have been reported with concomitant organic nitrate use. Avoid use of Viagra with organic nitrates. Priapism, sometimes requiring medical intervention has also been reported. Visual disturbances, usually mild and transient predominantly color tinge but occasionally blurred vision, has been reported. Caution should be used in the following patient types: Patients who have suffered a myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months; Patients with resting hypotension (BP <90/50) or hypertension (BP >170/110); Patients with cardiac failure or coronary artery disease causing unstable angina; Patients with retinitis pigmentosa (a minority of these patients have genetic disorders of retinal phosphodiesterases); Patients with sickle cell or related anemias.

Adverse reactions (side effects) of these medications: The most common side effects of Viagra include headache, flushing, dyspepsia, nasal congestion, urinary tract infection, abnormal vision, diarrhea, dizziness and rash. Other adverse events reported include arthritis, arthrosis, myalgia, angina, AV block, migraine, syncope, tachycardia, back pain, flu syndrome, and arthralgia.

Common drug interactions: Bocepravir, HIV protease inhibitors, nitrates, telaprevir, azole antifungals, clarithromycin, conivaptan, crizotinib, delapridine, erythromycins, fluvoxamine, imatinib, nefazodone, pazopanib, rufinamide, telithromycin and yohimbine have all been reported to have actual or theoretical interactions with Viagra.

Special instructions for patients: Take this medication exactly as directed by physician. Read the official Medication Guide before starting Viagra and when you receive new refills. Viagra must never be used by men who are taking medicines that. Contact physician or seek medical help for an erection lasting longer than 4 hours. If you experience sudden decrease or loss of vision, stop taking PDE5 inhibitors, including Viagra, and call a doctor right away.

Full prescribing information may be found at the manufacturer‘s official website Viagra.com or at the U.S. Food and Drug Administration’s website at Viagra Info at Drugs@FDA

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