While the 6MWD has been used as an end point in previous drug trials for pulmonary arterial hypertension, Dr. Taichman wrote that improvements in such a variable were “probably too modest to be unequivocally consequential for many patients.” To confirm the benefits – and detriments – of treatments like inhaled treprostinil, it’s time for studies to focus on clinical end points, he stated, including hospitalizations, disease progression, and death.
He also highlighted the disparity between a treatment that led to increased walk distance and decreased clinical worsening yet did not register an improvement in health-related quality of life. He noted that the oft-cited minimal clinically important difference for 6MWD is approximately 30 m – similar to the difference recorded here. That said, he wrote, “prevention of deterioration is not to be ignored, even if it does not make a patient feel better.”
Regarding quality of life, Dr. Tonelli observed that this questionnaire, standard fare in respiratory research, may not have been perfectly suited for this particular study.
“You have to put it in the context of, ‘How good is the questionnaire to capture a difference in this particular disease over a 16-week period?’ ” he said. “It might not be sensitive enough to capture a significant change. The questionnaire was not developed for pulmonary hypertension in interstitial lung disease, of course. It was developed more generically. It may not capture all that you need to show significance.”
The investigators acknowledged the study’s other potential limitations, including a short duration, a notable percentage of patients who discontinued the trial early, and the fact that clinical worsening and exacerbation of disease were investigator reported and not confirmed by an independent committee.
As for next steps in assessing pulmonary hypertension treatments, Dr. Tonelli pointed to the direction of future research. “The other big study that needs to come out in our field, and I believe it’s being worked on, is inhaled treprostinil in pulmonary hypertension due to chronic obstructive pulmonary disease [COPD],” he said. “That’s a major unmet need; the COPD population is larger than the population for interstitial lung disease, and one would wonder whether inhaled treprostinil would benefit those patients as well. At the moment, we have no treatments for that condition. In the future, a COPD study will be needed.”
The study was supported by United Therapeutics. Author disclosures are listed on the New England Journal of Medicine website.