Sildenafil: Effects, Dosage and Side Effects
Sildenafil is a prescription medication used to treat erectile dysfunction and pulmonary arterial hypertension. It works by relaxing blood vessels and improving blood flow.
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Sildenafil is a prescription medication used to treat erectile dysfunction and pulmonary arterial hypertension. It works by relaxing blood vessels and improving blood flow.
What is Sildenafil?
Sildenafil is an active pharmaceutical ingredient belonging to the class of phosphodiesterase type 5 (PDE-5) inhibitors. Originally developed for cardiovascular conditions, it is now primarily used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It is widely known under the brand names Viagra (for erectile dysfunction) and Revatio (for PAH).
Indications
Sildenafil is approved for the following medical conditions:
- Erectile dysfunction: The inability to achieve or maintain an erection sufficient for satisfactory sexual activity.
- Pulmonary arterial hypertension (PAH): Abnormally high blood pressure in the arteries of the lungs, which strains the heart and reduces exercise capacity.
Mechanism of Action
Sildenafil selectively inhibits the enzyme phosphodiesterase type 5 (PDE-5), which is found in the smooth muscle of blood vessel walls. By blocking this enzyme, sildenafil prevents the breakdown of cyclic guanosine monophosphate (cGMP). Elevated cGMP levels cause relaxation of smooth muscle cells in blood vessel walls, leading to vasodilation (widening of blood vessels). In erectile dysfunction, this increases blood flow into the penile erectile tissue, facilitating an erection. In PAH, it reduces pulmonary vascular resistance and relieves strain on the right side of the heart.
Dosage
The appropriate dosage of sildenafil depends on the condition being treated and should always be determined by a physician:
- Erectile dysfunction: The standard dose is 50 mg, taken approximately 30 to 60 minutes before sexual activity. The dose may be adjusted to 25 mg or increased to a maximum of 100 mg based on efficacy and tolerability. It should not be taken more than once per day.
- Pulmonary arterial hypertension: Typically 20 mg three times daily, evenly spaced throughout the day.
Sildenafil can be taken with or without food, although high-fat meals may delay its onset of action.
Side Effects
Like all medications, sildenafil can cause side effects. Commonly reported side effects include:
- Headache
- Facial flushing
- Indigestion (dyspepsia)
- Nasal congestion
- Visual disturbances (e.g., altered color perception, blurred vision)
- Dizziness
Rare but serious side effects may include sudden hearing loss, priapism (a prolonged and painful erection), and severe drops in blood pressure, particularly when taken with nitrates.
Contraindications and Drug Interactions
Sildenafil must not be used:
- In combination with nitrates (e.g., nitroglycerin), as this can cause a dangerous and potentially life-threatening drop in blood pressure.
- In patients with known hypersensitivity to the active substance.
- In patients with severe cardiovascular conditions where sexual activity is inadvisable.
- In patients with severe hepatic impairment.
Significant interactions also exist with other antihypertensive drugs, certain antibiotics (e.g., erythromycin), HIV protease inhibitors, and other PDE-5 inhibitors.
Usage Notes
Sildenafil is a prescription-only medication and should only be taken under medical supervision. Purchasing sildenafil from unregulated online sources carries serious health risks due to counterfeit products. It is important to note that sildenafil does not produce a spontaneous erection -- sexual stimulation is still required for the medication to be effective.
References
- European Medicines Agency (EMA): Summary of Product Characteristics -- Sildenafil, current edition.
- Rosen RC et al. - The Process of Care Model for Evaluation and Treatment of Erectile Dysfunction. International Journal of Impotence Research, 1999.
- Galie N et al. - 2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension. European Heart Journal, 2015.
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