The first patient was dosed in a multicenter phase 2 clinical trial testing RT234 for the treatment of pulmonary arterial hypertension (PAH), according to a press release from Respira Therapeutics, Inc., the developers of the treatment.

The start of the trial “is a critical next step in potentially offering patients with PAH an acute treatment to manage their shortness of breath, which prevents them from performing normal daily duties,” Carol Satler, MD, PhD, the president and chief medical officer of Respira, said. 

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RT234 is Respira’s lead drug-device product. It is a first-in-class inhaled therapy that aims to improve exercise tolerance in PAH patients and provide relief from breathlessness and fatigue.

Preclinical studies have shown RT234 has significant safety margins, and in phase 1 clinical studies, it had pharmacokinetic properties consistent with what is expected from an acute medication. 

The trial, called VIPAH-PRN, is an open-label, single-dose study that is evaluating the safety and efficacy of RT234 on exercise parameters as assessed by cardiopulmonary exercise testing in an estimated 40 patients with PAH.

Participants will receive RT234 as single doses administered using an Axial Oscillating Sphere dry powder inhaler.

The primary outcome measures include the incidence and severity of treatment-emergent adverse events and changes in blood pressure, peak oxygen consumption, patient global impression of severity, and duration of exercise.

“Enabling PAH patients to be more active is key to their physical and mental health,” Raymond L. Benza, MD, director of the Division of Cardiovascular Medicine at The Ohio State University Wexner Medical Center in Columbus, said. “Now with the study of RT234, we are examining our ability to boost physical activity when a patient needs it. It’s potentially a great step forward in our battle with this disease.”

The trial is still recruiting participants with PAH aged 18 to 80 years in the United States and Serbia. It is expected to be completed in July 2022.


Respira Therapeutics announces first patient dosed in phase 2b VIPAH-PRN 2b trial of RT234 in patients with pulmonary arterial hypertension (PAH). News release. Respira Therapeutics, Inc.; April 5, 2022. 

Effects of RT234 on exercise parameters accessed by CPET in subjects with PAH. February 12, 2020. Updated June 24, 2021. Accessed April 7, 2022.