Sildenafil
Quick Definition
Sildenafil is a short-acting PDE5 inhibitor FDA-approved for erectile dysfunction (Viagra) and pulmonary arterial hypertension (Revatio). Its onset is 30-60 minutes and clinical window is approximately 4 hours, with absorption sensitive to high-fat meals.
In Depth
Sildenafil received FDA approval in 1998 as Viagra for erectile dysfunction, the first oral medication for this indication. It is also approved at lower doses as Revatio for pulmonary arterial hypertension.
Like tadalafil, sildenafil inhibits phosphodiesterase type 5 (PDE5) in penile vascular smooth muscle, enhancing the vasodilatory response to sexual stimulation through cGMP preservation.
The half-life of sildenafil is approximately 4 hours, considerably shorter than tadalafil's 17.5 hours. This produces a clearer medication-on / medication-off window — onset typically 30-60 minutes after dosing, peak effect at 1 hour, clinical window of approximately 4 hours.
Sildenafil's absorption is meaningfully delayed and reduced by high-fat meals. Patients are typically counseled to take sildenafil on an empty stomach or with a light meal for reliable onset.
The side effect profile overlaps substantially with tadalafil: headache, flushing, nasal congestion, dyspepsia. Sildenafil is more associated with visual changes (a blue tint, related to weaker selectivity for PDE5 vs PDE6 in the retina) than tadalafil is. Serious but rare risks include priapism, sudden hearing loss, and NAION.
The contraindication with nitrates is shared and is the highest-priority interaction in this drug class.
Generic sildenafil is widely available at low cost since the patent expired. Generic versions are bioequivalent and clinically equivalent to branded Viagra at the FDA approval standard.
Related Terms
Tadalafil
Tadalafil is a long-acting PDE5 inhibitor FDA-approved for erectile dysfunction (Cialis) and benign prostatic hyperplasia. Its 17.5-hour half-life produces a 24-36 hour clinical window, supporting both on-demand and daily low-dose dosing schedules.
PDE5 Inhibitor
A PDE5 inhibitor is a medication that inhibits the enzyme phosphodiesterase type 5, which degrades cyclic guanosine monophosphate (cGMP) in vascular smooth muscle. The class is FDA-approved for erectile dysfunction and pulmonary arterial hypertension, and includes sildenafil, tadalafil, vardenafil, and avanafil.