Same mechanism as sildenafil but with a 17.5-hour half-life. The 'weekend pill'. Works for ~36 hours. Daily low-dose (2.5-5mg) is widely used for ED, BPH symptoms, and cardiovascular/metabolic effects.
Dose: 2.5-5mg daily for chronic use, or 10-20mg as-needed.
Caveats: Same nitrate interaction as sildenafil. Slightly higher rate of muscle aches and back pain.