Which medication is primarily used to treat pulmonary arterial hypertension?

Epoprostenol is a synthetic form of prostacyclin, which is a potent vasodilator specifically effective for treating pulmonary arterial hypertension (PAH). It works by relaxing the blood vessels in the lungs and improving blood flow, thereby reducing the high blood pressure in the pulmonary arteries. This action is crucial for patients with PAH as it alleviates symptoms such as shortness of breath and improves exercise capacity.

In addition to its vasodilatory effects, epoprostenol also inhibits platelet aggregation, which can be beneficial in this patient population. It is administered intravenously due to its very short half-life, requiring continuous infusion in clinical settings.

The other medications mentioned do not primarily address PAH. Misoprostol is used primarily for gastric protection and inducing labor, alprostadil is mainly used for erectile dysfunction and maintaining patent ductus arteriosus in neonates, and febuxostat is a treatment for gout and hyperuricemia. Thus, the specific action of epoprostenol in pulmonary arterial hypertension makes it the correct choice in this context.