To examine how rescue medication is defined, reported and accounted for in randomised controlled trials (RCTs) in eczema and asthma populations.
A systematic review of phase II/III RCTs evaluating monoclonal antibodies for treating chronic eczema or asthma. A search of EMBASE, MEDLINE and the Cochrane Central Register of Controlled Trials was conducted to identify eligible RCTs.
Sixty published RCTs were identified, of which 60 (100%) allowed use of rescue medication but only 28 (47%) reported its use. Twenty-seven (45%) articles summarised rescue use by arm, with an average of 25% (95% CI (17%, 36%)) greater use in the placebo arm. Nine (15%) trials undertook an analysis that adjusted the primary treatment effect estimate for rescue medication use, but 8 of these employed a sub-optimal approach using single imputation, including 4 which used ‘last observation carried forward’ after setting post-rescue data to missing.
Rescue medication use in eczema and asthma trials evaluating monoclonal antibodies is often permitted, but not routinely reported. There is evidence of imbalance in rescue use between arms, but few articles attempted to estimate a rescue-adjusted treatment effect. In trials that did, the methods employed were sub-optimal which could introduce bias.

Copyright © 2020. Published by Elsevier Inc.