Sildenafil

Generic Name: Sildenafil
Common Brand Names: Viagra, Revatio

Introduction

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It was originally developed for the treatment of hypertension but is more commonly known for its use in treating ED.

Conditions of Use (Indications)

1. Erectile Dysfunction: Sildenafil is primarily used for the treatment of erectile dysfunction in men.
2. Pulmonary Arterial Hypertension: It is used under the brand name Revatio for managing pulmonary hypertension to improve exercise capacity and reduce symptoms.

Mechanism of Action

Sildenafil works by inhibiting the enzyme PDE5, which is responsible for the breakdown of cyclic GMP (cGMP) in the corpus cavernosum of the penis. The increase in cGMP levels leads to smooth muscle relaxation and vasodilation, which improves blood flow and results in an erection in the presence of sexual stimulation. In the lungs, sildenafil reduces pulmonary vascular resistance by relaxing vascular smooth muscle.

Side Effects

1. Common:

• Headache, flushing, dyspepsia (indigestion), and nasal congestion.
• Visual disturbances, including blue-tinted vision or light sensitivity.

2. Serious:

• Priapism (prolonged erection), which requires urgent medical attention.
• Sudden vision loss or hearing loss.
• Myocardial infarction (heart attack), particularly in those with pre-existing cardiovascular disease.

Harmful Interactions

1. Nitrates: Concurrent use of sildenafil with nitrates (e.g., nitroglycerin) can cause a dangerous drop in blood pressure.
2. Alpha-blockers: Sildenafil may potentiate the blood-pressure-lowering effects of alpha-blockers (used for hypertension or benign prostatic hyperplasia).
3. CYP3A4 Inhibitors: Drugs like ketoconazole and erythromycin may increase sildenafil levels, increasing the risk of side effects.

Contraindications

1. Concurrent use with nitrates or nitric oxide donors.
2. Severe cardiovascular disorders, including recent myocardial infarction, stroke, or unstable angina.
3. Known hypersensitivity to sildenafil or any of its components.

Latest References

1. D’Amico, G., et al. (2023). “The Efficacy and Safety of Sildenafil in Erectile Dysfunction.” Journal of Urology, DOI: 10.1016/j.juro.2023.05.016.
2. American College of Cardiology (ACC). (2022). “Phosphodiesterase-5 Inhibitors in Cardiovascular Disease.” ACC Guidelines.