Among the most commonly used therapies to treat pulmonary arterial hypertension (PAH) are the prostanoids. Epoprostenol, a relatively effective therapy for PAH, has its limitations, which are largely attributable to its pharmacokinetic properties and its requirement for intravenous administration. The development of an equally effective oral prostanoid would be an important advance in the PAH armamentarium. An early generation oral prostanoid, beraprost, was previously demonstrated to have modest, transient clinical benefits, but at the cost of a high proportion of intolerable side effects. TRK-100STP is a newer generation oral prostanoid currently under clinical investigation.