Pandemic Blamed for Failed Trial of Inhaled Antibiotic

Ted Bosworth

July 31, 2023

NEW YORK, New York — When data were combined from two parallel phase 3 bronchiectasis treatment trials, inhaled colistimethate sodium failed to significantly reduce the rate of exacerbations associated with Pseudomonas aeruginosa infection, but the disparity in the findings from the two trials, presented at the 6th World Bronchiectasis & NTM Conference (WBC) 2023, strongly suggest that this therapy is effective after all.

"The totality of the evidence supports a consistent and clinically meaningful benefit [of this therapy] outside of pandemic conditions," reported Charles Haworth, MD, director, Cambridge Centre for Lung Infection, Royal Papworth Hospital, Cambridge, England.

The key phrase is "outside of pandemic conditions," PROMIS I, which was fully enrolled before the COVID-19 pandemic descended, associated the inhaled therapy with highly significant benefits. PROMIS II, which was initiated later and enrolled 40% of its participants during the pandemic, did not.

The difference between these two trials, which were essentially identical, was the timing, according to Haworth. By starting later, PROMIS II caught the onset of the pandemic, which he believes introduced numerous problems that defeated the opportunity to show an advantage for the inhaled antibiotic.

Injectable colistimethate sodium, a decades-old formulation of colistin, is already approved in the US for gram negative infections and is considered helpful even in challenging diseases, such as cystic fibrosis. Positive results from a phase 2 trial with inhaled colistimethate sodium in bronchiectasis patients with P. aeruginosa infection provided the rationale for the phase 3 PROMIS program.

The key entry criterion of PROMIS I and PROMIS II, each with nearly 90 participating study sites, was a history of bronchiectasis and ≥ two P. aeruginosa infections requiring oral therapy or ≥ 1 infection requiring intravenous therapy in the prior 12 months. Patients were randomly assigned to receive colistimethate sodium delivered in the proprietary I-neb nebulizer (CMS I-neb) or a matching placebo.

On the primary endpoint of annualized rate of exacerbations, the figures per year were 0.58 for CMS I-neb and 0.95 for placebo in the PROMIS I trial. This produced a rate ratio of 0.65, signaling a significant 35% (P = .00101) reduction in risk. In PROMIS II, the annualized rates of exacerbation were essentially identical in the experimental and control arms (0.089 vs. 0.088; P = .97).

With "no signal of benefit" in the PROMIS II trial, the numerical advantage of CMS I-neb for the combined data did not reach statistical significance, Haworth reported.

Other endpoints told the same story. For example, the time to first exacerbation was reduced by 41% in PROMIS I (HR, 0.59; P = .0074) but was not reduced significantly (P = .603) in PROMIS II. In PROMIS I, there was a nearly 60% reduction in the risk of severe exacerbations associated with CMS I-neb, but the risk ratio of severe infections was slightly but not significantly higher on CMS I-neb in PROMIS II.

There were signals of benefit in PROMIS II. For example, the reductions in P. aeruginosa density were similar in the two studies (P < .00001 in both), and assessment with the Severe Exacerbations and Quality of Life (SQOL) tool associated CMS I-neb with end-of-study improvement in QOL for the experimental arm in both studies.

While Haworth acknowledged that he recognizes the "issues of post hoc analysis with any data," he argued that there is compelling evidence that the pandemic "severely disrupted the conduct of the trial," obscuring a benefit that would have been otherwise shown.

Besides the dramatic reduction in rates of hospitalization during the pandemic, an obstacle for showing differences in exacerbations, and other COVID-related factors with the potential to skew results, Haworth also provided several sets of objective data to make his point.

Most importantly, Haworth and his coinvestigators conducted a meta-analysis that combined data from the phase 2 trial, data from PROMIS I, and data from the patients enrolled in PROMIS II prior to the COVID pandemic. In this analysis the rate ratio for annualized exacerbations was a "pretty impressive" 0.65 favoring CMS I-neb. Moreover, in contrast to data from the PROMIS II patients enrolled during the COVID pandemic, the other three sets of data were "remarkably consistent."

If PROMIS II data collected from patients enrolled during COVID are compared with the other sets of data, they are "the clear outlier," he asserted.

Many guidelines in Europe, including those from the European Respiratory Society and the British Thoracic Society, already recommend inhaled colistin in patients with bronchiectasis for the treatment of P. aeruginosa. Although Haworth believes that the preponderance of controlled data now argue that CMS I-neb is effective as well as safe (adverse events in the experimental and placebo arms of PROMIS I and II were similar), he is not sure what steps will be taken to confirm a benefit to regulatory authorities. According to Haworth, there are no approved inhaled antibiotics in the United States.

Referring to Zambon, which funded the trials and is developing CMS I-neb, Haworth said, "This will be a company decision. There are some logistical hurdles to doing another trial."

Not least of these hurdles is that clinicians and patients already consider inhalational antibiotics in general and inhaled colistin specifically to be effective for several types of infections, including P. aeruginosa, according to Eva Polverino, MD, PhD, a pulmonologist associated with the Hospital Clinic of Barcelona, Spain. She said that these drugs are already a standard of care in her own country as well as in many other countries in Europe.

"There has been a loss of equipoise needed to conduct a randomized placebo-controlled trial," Polverino said. In her opinion, the US FDA "should start thinking of other pathways to approval." She thinks that enrollment in a placebo-controlled trial is no longer appropriate.

Haworth and Polverino have disclosed no relevant financial relationships.

6th World Bronchiectasis & NTM Conference (WBC) 2023. Presented July 20, 2023.

For more news, follow Medscape on Facebook, Twitter, Instagram, and YouTube.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.