Sildenafil – Potent PDE5 Inhibitor for Erectile Dysfunction and PAH
Sildenafil is the world's first potent, selective, and reversible oral inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE-5). The drug was developed for the pathogenic therapy of erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Its mechanism of action involves blocking the PDE-5 enzyme, which is responsible for the degradation of cGMP in vascular smooth muscle cells. Inhibition of PDE-5 leads to a pronounced accumulation of cGMP, thereby enhancing the relaxant effect of endogenous nitric oxide (NO) on the smooth muscle of the corpus cavernosum and pulmonary vasculature, causing active arteriole dilation and increased local blood flow.
The historical and clinical significance of sildenafil lies in its role as the pioneer of the oral PDE-5 inhibitor class, which revolutionized the field of andrology. Unlike long-acting analogs (such as tadalafil), sildenafil is a short-acting agent with a half-life of approximately 3 to 5 hours, providing a well-predicted therapeutic window of up to 4 to 5 hours. The drug also exhibits a marked ability to reduce resistance in the pulmonary vascular bed and decrease right ventricular workload, which is why it is successfully utilized in cardiology under a distinct trade name. Sildenafil is rapidly absorbed following oral administration, though its bioavailability and onset of action can be significantly delayed when taken with high-fat meals or alcohol.
The drug is administered orally. To manifest a therapeutic effect for erectile dysfunction, the presence of natural sexual stimulation and arousal is an absolute and key prerequisite.
Indications
Sildenafil is indicated for the treatment of adult patients with the following pathological conditions:
- Erectile Dysfunction: treatment of erectile disturbances, defined as the inability to achieve or maintain a penile erection sufficient for satisfactory sexual performance.
- Pulmonary Hypertension (PAH): pathogenic therapy for pulmonary arterial hypertension (including primary PAH and PAH associated with connective tissue disease) to improve exercise capacity.
Dosage and administration
The dosing regimen of sildenafil is established individually based on clinical indications, efficacy, and patient tolerability.
- For "on-demand" ED therapy: the recommended starting dose is 50 mg, taken approximately 1 hour before anticipated sexual activity. Based on efficacy and tolerability, the dose may be increased to 100 mg or decreased to 25 mg. The maximum recommended dosing frequency is once daily.
- For Pulmonary Arterial Hypertension (PAH): the standard dosage is 20 mg taken three times daily (approximately 6 to 8 hours apart), with or without food.
- Administration Method: tablets are swallowed whole with water. For the fastest onset of action, administration on an empty stomach is recommended.
- Dose Adjustment: in elderly patients (over 65 years of age) and individuals with severe renal or hepatic impairment, the initial dose for ED treatment should be limited to 25 mg.
