Q: Beside Erectile Dysfunction (ED) and Pulmonary Hypertension (PAH), Sildenafil is an acceptable treatment in which condition?

Answer: Altitude sickness

The phosphodiesterase 5 (PDE-5) inhibitors (both, sildenafil and tadalafil) have effectively shown to prevent hypoxic pulmonary hypertension. They have used for the prevention as well as treatment of high-altitude pulmonary edema occur in altitude sickness. Different doses have been described for sildenafil, from a single dose of 50 or 100 mg just prior to exposure for acute ascent, to 40 mg three times a day while at high altitude. For tadalafil, 10 mg every 12 hours is the described dose.

References: 

1. Richalet JP, Gratadour P, Robach P, et al. (2005). "Sildenafil inhibits altitude-induced hypoxemia and pulmonary hypertension". Am. J. Respir. Crit. Care Med. 171 (3): 275–81.

2.Perimenis P (2005). "Sildenafil for the treatment of altitude-induced hypoxaemia". Expert Opin Pharmacother 6 (5): 835–7. 

3.  Fagenholz PJ, Gutman JA, Murray AF, Harris NS (2007). "Treatment of high altitude pulmonary edema at 4240 m in Nepal". High Alt. Med. Biol. 8 (2): 139–46.

4. Ghofrani HA, Reichenberger F, Kohstall MG, et al. Sildenafil increased exercise capacity during hypoxia at low altitudes and at Mount Everest base camp: a randomized, double-blind, placebo-controlled crossover trial. Ann Intern Med 2004; 141:169.