Prostacyclin and its analogues (prostanoids) are potent vasodilators, and exhibit antithrombotic, antiproliferative and anti-inflammatory properties. Pulmonary arterial hypertension (PAH) is characterised by vasoconstriction, thrombosis and proliferation, and is associated with reduced synthesis of endogenous prostacyclin. This provides a strong rationale for the use of prostanoids to treat PAH, a concept that is now supported by more than two decades of clinical research and experience.

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... nous and subcutaneous prostanoids have clearly demonstrated efficacy in severe PAH, but adverse events related to the drug delivery system, systemic side-effects and tachyphylaxis have driven research into alternative prostanoid treatments. Iloprost is administered by inhalation, and thus avoids most of the systemic side-effects associated with i.v. or subcutaneous prostanoid infusion. Two randomised controlled 12-week trials in patients with PAH have demonstrated efficacy and a favourable safety profile for iloprost as monotherapy (the AIR trial) and in combination with oral bosentan (STEP). Open-label uncontrolled long-term studies of inhaled iloprost therapy indicate that this treatment may improve long-term outcomes in PAH.