Sildenafil has the potential to improve hemodynamics and exercise capacity for up to 12 months in children with Pulmonary arterial hypertension (PAH), and this medication can be compounded as a stable oral suspension.

Circulation. 2005 Jun 21;111(24):3274-80
Beneficial effect of oral sildenafil therapy on childhood pulmonary arterial hypertension: twelve-month clinical trial of a single-drug, open-label, pilot study.
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Am J Health Syst Pharm. 2006 Feb 1;63(3):254-7
Extemporaneous sildenafil citrate oral suspensions for the treatment of pulmonary hypertension in children.
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