Sildenafil
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PDE5 Inhibitor
Sildenafil
Viagra, Revatio
Sildenafil was the first PDE5 inhibitor (FDA-approved 1998) and remains the prototype. Originally developed for angina; repurposed after a famous trial-side-effect observation. Same molecule is marketed as Revatio for pulmonary arterial hypertension at lower individual doses but higher daily totals.
Blood pressure with concurrent antihypertensives or alpha-blockers.
Contraindicated with any nitrate, life-threatening hypotension. Caution with alpha-blockers, separate doses by ≥4 h. The "blue tint" visual side effect comes from PDE6 cross-reactivity in retinal cones.
Avanafil, Tadalafil, Vardenafil
Experience
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Effects
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Pharmacokinetics
Absorption
~40%; reduced by high-fat meals.Distribution
Plasma protein binding ~96%.Metabolism
Hepatic via CYP3A4 (primary), CYP2C9.Elimination
Mainly fecal as metabolites.Interactions
No interactions reported yet.
Monitoring
Patient counseling
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See also
References
Summary
Classes
PDE5 Inhibitor
Common uses
Erectile dysfunction0, Pulmonary arterial hypertension0
Pharmacy
Starting dose
50 mg ~1 h before sexual activity (ED); 20 mg TID (PAH)
Preparations
25, 50, 100 mg tabs (Viagra); 20 mg tabs and 10 mg/mL oral suspension (Revatio)
US FDA Max
100 mg/d (ED); 20 mg TID (PAH)
Pharmacology
Routes
Oral, IV (Revatio)
Onset
30–60 min
Duration
~4 h
Half-life
~4 h
Bioavailability
~40%
Pregnancy
Category B
Legal status
Rx-only in US
Purported mechanism
Selective inhibitor of phosphodiesterase type 5 (PDE5), preventing cGMP breakdown in vascular smooth muscle. In the corpus cavernosum, potentiates the NO/cGMP cascade triggered by sexual stimulation.