Pharmacologic Class: Phosphodiesterase (PDE)-5 inhibitor
ACTIONS AND USES: Sildenafil acts by relaxing smooth muscles in the corpora cavernosa, thus allowing increased blood flow into the penis. The increased blood flow results in a firmer and longer lasting erection in about 70% of men taking the drug. The onset of action is relatively rapid, less than 1 hour, and its effects last up to 4 hours. Sildenafil blocks the enzyme phosphodiesterase-5. Sildenafil is also used for the treatment of pulmonary arterial hypertension. Blocking phosphodiesterase-5 in pulmonary vascular smooth muscle causes vasodilation and reduction in arterial hypertension. The drug improves exercise capacity in these patients. An off-label indication for sildenafil is the treatment of Raynaud’s phenomenon resistant to vasodilator therapy.
ADMINISTRATION ALERTS: Avoid administration of sildenafil with meals, especially high-fat meals, because absorption is decreased. Avoid grapefruit juice when administering sildenafil.
ADVERSE EFFECTS: Sildenafil is well tolerated and adverse effects are usually transient and mild. Common adverse effects include headache, dizziness, flushing, rash, and nasal
congestion. The most serious adverse effect, hypotension, occurs in patients concurrently taking organic nitrates for angina and can result in myocardial infarction (MI) and sudden cardiac death. Sildenafil can produce blurred vision, increased sensitivity to light, or changes in color perception. Priapism, a sustained erection lasting longer than 6 hours, has been reported with sildenafil use and this may lead to permanent damage to penile tissues. Contraindications: Sildenafil is contraindicated in patients taking nitrates and in those with hypersensitivity to the drug. These drugs are contraindicated in patients with severe cardiovascular disease, recent MI, stroke, heart failure, dysrhythmias, and in the presence of anatomic deformities of the penis.
INTERACTIONS: Drug–Drug: Cimetidine, erythromycin, and ketoconazole will increase serum levels of sildenafil and necessitate lower drug doses. Use with nitrates will result in hypotension. Protease inhibitors (ritonavir, amprenavir, others) will cause increased sildenafil levels, which may lead to toxicity. Rifampin may decrease sildenafil levels, leading to decreased effectiveness.
Herbal/Food: Administration of sildenafil with high-fat meals decreases the absorption of the drug. Grapefruit juice increases the plasma concentrations of sildenafil and may cause adverse effects.
Treatment of Overdose: There is no specific treatment for overdose.
RELATED;
1. BENIGN PROSTATIC HYPERPLASIA
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