Sildenafil

Sildenafil, a phosphodiesterase-5 (PDE5) inhibitor, is primarily indicated for the treatment of erectile dysfunction by enhancing nitric oxide-mediated vasodilation in the corpus cavernosum, leading to improved erectile function, rapid onset within 14 minutes in some patients, and efficacy even in challenging subpopulations such as those with diabetes or post-prostatectomy.¹,² It is also FDA-approved for pulmonary arterial hypertension (PAH, WHO Group I) in adults to improve exercise capacity, delay clinical worsening—particularly when added to epoprostenol—and reduce pulmonary arterial pressures, with demonstrated benefits in pediatric patients aged 1-17 years for primary PAH or that associated with congenital heart disease.¹,³ Additional evidence supports hemodynamic improvements like reduced systolic blood pressure and enhanced exercise performance in cardiovascular and pulmonary diseases, alongside symptom relief such as decreased breathlessness and fatigue.¹,³

Sildenafil commonly causes mild, short-lived side effects such as headache, flushing, heartburn or indigestion, nasal congestion, nausea, diarrhea, dizziness, and vision changes like blurred or color-tinged sight.⁴,⁵,⁶ Serious side effects requiring immediate medical attention include sudden vision or hearing loss, chest pain, prolonged or painful erection (priapism) lasting over 4 hours, severe dizziness or fainting, and signs of allergic reaction like rash, swelling, or breathing difficulty.⁴,⁷,⁸ Key safety considerations involve avoiding use with nitrates for chest pain due to risk of severe low blood pressure, discussing cardiovascular risks especially with pre-existing heart conditions, and noting higher doses increase side effect likelihood.⁴,⁵,⁹ Patients with recent heart attack, stroke, or certain eye conditions should consult a doctor, as rare events like non-arteritic anterior ischemic optic neuropathy (NAION) have been reported.⁴,⁷ Most side effects resolve without intervention, but persistent or severe symptoms warrant prompt medical evaluation.⁶,⁸

Sildenafil is a selective inhibitor of phosphodiesterase type 5 (PDE5), an enzyme responsible for degrading cyclic guanosine monophosphate (cGMP).¹,¹⁰,¹¹ During sexual stimulation, nitric oxide (NO) release activates guanylate cyclase, increasing cGMP levels in the corpus cavernosum, which promotes smooth muscle relaxation and vasodilation to facilitate erection; sildenafil enhances this by preventing cGMP breakdown, allowing its accumulation.¹⁰,¹¹,¹² This leads to cGMP-dependent protein kinase activation, decreasing intracellular calcium, deactivating myosin light chain kinase, and causing prolonged smooth muscle relaxation.¹⁰,¹¹ In pulmonary arterial hypertension, the same mechanism relaxes pulmonary vascular smooth muscle, reducing blood pressure.¹,¹⁰ Sildenafil requires sexual stimulation or NO release to be effective, as it has no direct relaxant effect.¹¹,¹²