Sildenafil citrate, the active compound in Viagra, inhibits an enzyme called phosphodiesterase-5 (PDE5). This inhibition increases blood flow to the penis, facilitating an erection. Understanding this mechanism is key to appreciating its effects and potential side effects.
Pharmacokinetics and Metabolism
Oral administration results in peak plasma concentrations within 30-120 minutes. Sildenafil is primarily metabolized by the liver, with a half-life of approximately 4 hours. This relatively short half-life contributes to the predictable duration of its effects. Renal excretion accounts for a significant portion of elimination. Dosage adjustments are needed for individuals with hepatic or renal impairment.
Common Side Effects
Headache, flushing, and nasal congestion are the most frequently reported side effects. These are usually mild and transient. More serious, though less common, side effects include vision changes (blurred vision, blue tinge), hypotension, and heart problems. Consult a physician immediately if you experience any concerning symptoms.
Drug Interactions
Nitrates, used to treat angina, should be avoided with sildenafil due to the risk of severe hypotension. Also, caution is advised when combining it with alpha-blockers (used for hypertension) or certain antifungal medications. A doctor can provide detailed guidance on potential interactions based on your specific medications.
Contraindications
Individuals with severe cardiovascular disease, uncontrolled hypertension, recent stroke or myocardial infarction, and those with a known hypersensitivity to sildenafil should not use this medication. Additionally, those with retinitis pigmentosa should exercise extreme caution. Always inform your doctor of your complete medical history.
