Category:PDE5 Inhibitors

Phosphodiesterase type 5 (PDE5) inhibitors block the enzyme that degrades cyclic guanosine monophosphate (cGMP) in vascular smooth muscle. By preserving cGMP signaling downstream of nitric oxide, they enhance vasodilation in the corpus cavernosum (treating erectile dysfunction) and the pulmonary vasculature (treating pulmonary arterial hypertension).

• Sildenafil (Viagra, Revatio) — first-in-class, FDA-approved 1998, half-life ~4 h
• Vardenafil (Levitra, Staxyn) — similar profile to sildenafil
• Tadalafil (Cialis, Adcirca) — long-acting, half-life ~17.5 h ("weekend pill")
• Avanafil (Stendra) — newer, faster onset (~15 min), more selective

• Absolutely contraindicated with any nitrate — life-threatening hypotension
• Caution with alpha-blockers — separate doses by ≥4 h
• Avoid in patients where sexual activity itself is contraindicated by cardiovascular instability
• All metabolized through CYP3A4 — strong inhibitors (azoles, protease inhibitors) raise levels