Pharmaceutical formulations are described for use in the treatment of pulmonary arterial hypertension (PAH). The formulations comprise polymeric nanoparticles encapsulated within crosslinked polymeric hydrogel microparticles, wherein the polymeric nanoparticles carry a therapeutic agent suitable for treatment of PAH loaded within them (for example, prostacyclin synthetic analogs, PPAR β agonists and NO donors). Preferred formulations are inhalable, dry powder pharmaceutical formulations, which are able to swell on administration to the lungs of a patient.