Biologics halved severe asthma attacks in practice, and spirometry exclusions did not predict response

Design

Self-controlled case series within a prospective cohort, plus meta-analysis of 6 trials

Population

480 US adults with severe asthma at 85 subspecialist sites

Primary outcome

Severe exacerbation rate on vs off biologic

Effect

IRR 0.43 (95% CI 0.39–0.48) real world; RR 0.53 (0.47–0.60) in trials

CHRONICLE is a prospective US cohort of adults with severe asthma under subspecialist care. This analysis used a self-controlled case series in 480 patients from 85 sites, comparing exacerbation rates while on and off a biologic, and set it against a meta-analysis of six registration trials.

Biologics reduced severe exacerbations by 57% in practice (IRR 0.43) and by 47% in the trials (RR 0.53). Patients who would have met trial criteria for raised FeNO or eosinophils, minimal smoking history and prior exacerbations benefited more. Exclusions based on COPD, bronchiectasis or FEV1 — which would have kept the most real patients out of trials — did not change the response.

This matters because many patients seen in clinic would never have qualified for the trials that licensed these drugs. For them, the result is reassuring.

The self-controlled design removes fixed differences between patients but can be biased by regression to the mean if biologics start after a run of bad exacerbations. Biologic access in India remains limited by cost.

• Check FeNO, blood eosinophils and exacerbation history when selecting patients for a biologic.
• Do not exclude a patient with severe asthma from a biologic only because of fixed airflow obstruction or coexisting bronchiectasis.
• Record exacerbation rates for a year before and after starting, to judge response.
• Support smoking cessation, since smokers responded less.

Why it matters

It suggests trial eligibility rules based on spirometry may exclude patients who would benefit.

Don't overread it

Subgroup comparisons in an observational design are hypothesis-generating, not proof of who will respond.

The statistics, in plain English

An incidence rate ratio of 0.43 means 57% fewer exacerbations during biologic exposure. A ratio of IRRs of 0.65 for eosinophils means the reduction was about a third greater in patients with raised counts. Self-controlled designs compare each patient with themselves, but can exaggerate benefit if treatment starts at a peak.

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