Description
Sildenafil (Viagra) is the first clinically used PDE-5 inhibitor and one of the best-researched substances in pharmacology. Pfizer originally discovered the substance as an antihypertensive; the erection-promoting action was observed as an unexpected side effect in Phase 1 studies. Approved in 1998, Sildenafil made ED therapy a mass market.
Per study reports Sildenafil blocks phosphodiesterase type 5 (PDE-5). Like all PDE-5 inhibitors, the substance raises cGMP concentrations in vascular smooth muscle. In the penis this leads to vasodilation of corpus cavernosum arteries with sexual stimulation.
Pharmacokinetics are favorable for an on-demand profile: action begins 30-60 min after oral intake, plasma peak after 60 min, half-life about 3-5 hours. Action typically holds 4-6 hours - shorter than Tadalafil, but longer than some alternatives like Vardenafil.
An important pharmacokinetic property: fatty meals significantly reduce Sildenafil bioavailability (up to 40%). In study settings Sildenafil is therefore dosed at least 1 hour before food or 2 hours after a fatty meal.
In research beyond the ED area, Sildenafil shows interesting applications: pulmonary hypertension (brand name Revatio), altitude sickness prevention, and in some studies performance enhancement in high-altitude hypoxic environments.
Known effects: headache (most common side effect), facial flushing, dyspepsia, nasal congestion, in rare cases blue-green visual disturbance (PDE-6 cross-reaction at the optic nerve).
You can order Sildenafil as oral tablets in one bottle with 100mg per tablet.
This information is for research and educational purposes only. No medical recommendations.
Risks & Safety
Sildenafil sits in the mid range of the risk scale. As the best-researched PDE-5 inhibitor the compound is extensively characterized, but one interaction is serious.
Documented in studies and the literature:
- Nitrate interaction: combination with nitrates or nitric oxide donors is contraindicated due to the blood pressure synergy - the most serious of the known interactions.
- Headache: headache is the most commonly documented side effect.
- Facial flushing and nasal congestion: flushing, nasal congestion and dyspepsia are consistently documented as vasodilatory effects.
- Visual disturbance: in rare cases a blue-green visual disturbance is documented (PDE-6 cross-reaction at the optic nerve).
- Priapism risk: a prolonged painful erection is a documented rare risk of the PDE-5 inhibitor class.
Monitoring via bloodwork is recommended. This classification does not replace medical advice. Risk and responsibility for any actual use lie entirely with the buyer.
Studies
- Oral Sildenafil in the Treatment of Erectile Dysfunction - NEJM 1998, Goldstein et al: Gold-standard approval study of dose-dependent efficacy.
- Assessment of the efficacy and safety of Viagra (sildenafil citrate) in men with erectile dysfunction during long-term treatment - International Journal of Impotence Research 2001, Steers et al: Long-term data from open-label extension studies over 36 to 52 weeks.
- Sildenafil Citrate Therapy for Pulmonary Arterial Hypertension - NEJM 2005, Galie et al: RCT on the off-label application in pulmonary arterial hypertension.
