- Healthy males between the ages of 18 and 55 years.
- Body Mass Index of 18 to 30 kg/m2, and a total body weight >50 kg (110 lbs).
- Smoking in excess of the equivalent of 5 cigarettes per day.
- Treatment with an experimental drug within 30 days or sildenafil, vardenafil, tadalfil
within 4 days before first study dose.
- Develop blood pressure lowering or experience dizziness, lightheadedness when going
from the laying down position to standing position.