Tadalafil is a PDE5 inhibitor (phosphodiesterase type 5 inhibitor).
Inhibits PDE5 → prevents breakdown of cGMP → smooth muscle relaxation → vasodilation.
Effects are seen in penile vasculature, pulmonary vasculature, and the bladder neck/prostate.
Indications
Erectile dysfunction (Cialis) — 10–20 mg on-demand or 2.5–5 mg daily.
Longest duration of action among PDE5 inhibitors (~36 hours), earning it the nickname “the weekend pill.”
Benign prostatic hyperplasia (BPH) — 5 mg daily. Relaxes smooth muscle in the bladder neck and prostate, improving urinary flow.
Can treat ED and BPH simultaneously.
Pulmonary arterial hypertension (Adcirca/Alyq) — 40 mg once daily.
Reduces pulmonary vascular resistance and improves exercise capacity.
Contraindications Nitrates (any form) — risk of severe, potentially fatal hypotension
Riociguat (sGC stimulator) — risk of severe, potentially fatal hypotension
Severe hepatic impairment
Recent stroke or MI, or unstable angina
Side effects Headache, flushing, dyspepsia are most common
Back pain and myalgia — unique to tadalafil due to PDE11 inhibition
Visual disturbances-NAION risk, particularly with pre-existing optic nerve disease
Priapism
Drug interactions
Alpha-blockers — additive hypotension; used with caution
Strong CYP3A4 inhibitors (e.g. ketoconazole, ritonavir) — increase tadalafil levels and dose reduction needed
Renal/hepatic dosing Dose adjustment required in moderate renal impairment (CrCl 30–50); avoid in severe renal or hepatic impairment.