Emerging treatments
Imatinib
Imatinib is a tyrosine kinase inhibitor used to treat some types of cancer. It was investigated in a phase 3 clinical trial for the treatment of PAH; it was found to improve exercise capacity and haemodynamics in patients with advanced PAH, but resulted in substantial adverse events, and discontinuations were common.[89] An inhaled formulation of imatinib has been granted orphan drug designation by the FDA, and trials are ongoing.
Tacrolimus
Tacrolimus is a calcineurin inhibitor and immunosuppressant drug in clinical use for the prevention of organ rejection in transplant recipients. In animal models, low-dose tacrolimus activates bone morphogenetic protein receptor type 2 (BMPR2), rescues endothelial dysfunction, and reverses pulmonary hypertension.[90] Low-dose tacrolimus was given to three patients with end-stage PAH on a compassionate basis and led to significant improvements in functional capacity, serological markers, and BMPR2 markers of activity, and decreased hospitalisations.[91] A phase 2a trial showed that low-dose tacrolimus is well tolerated and increases BMPR2 in subsets of PAH patients.[92] A phase 2b efficacy trial is planned.
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