Background: Subcutaneous treprostinil has dose-dependent beneficial effects in patients with severe pulmonary arterial hypertension, but adverse effects like infusion site pain can lead to treatment discontinuation. Objectives: The objective of this study was to evaluate safety, tolerability and clinical effects of a rapid up-titration dosing regimen of subcutaneous treprostinil using proactive infusion site pain management. Methods: Effects of rapid up-titration dosing regimen on tolerability and clinical parameters were evaluated in this 16-week, open-label multi-centre study. Results: Thirty-nine patients with idiopathic or heritable pulmonary arterial hypertension on stable treatment with oral pulmonary arterial hypertension-approved drugs (90% on dual combination therapy) were included. Patients achieved a median treprostinil dosage of 35.7 ng/kg/min after 16 weeks. A good overall safety profile was demonstrated with 3 patients (8%) withdrawing due to infusion site pain, which occurred in 97% of patients. After 16 weeks, median 6-min walking distance, cardiac index, pulmonary vascular resistance, and tricuspid annular plane systolic excursion improved. Conclusions: Rapid up-titration of subcutaneous treprostinil was well tolerated, achieving a clinically effective dose associated with improvement of exercise capacity and haemodynamics after 16 weeks. A rapid dose titration regimen and proactive infusion site pain management may improve the handling of this therapy and contribute to better treatment outcome.