Placebo responses in randomized controlled trials for systemic therapy in atopic dermatitis: A systematic review and meta-analysis

Atopic dermatitis (AD) has a variable disease course and intermittent triggers, and responses to topical therapy vary, potentially affecting the magnitude of the placebo response in AD trials. To determine the predictors of increased placebo response in randomized controlled trials of AD. We performed a systematic review and meta-analysis of randomized controlled trials for systemic therapy in AD published during 2007-2018. We searched the Cochrane Library, Medline, Embase, Global Resource for EczemA Trials (GREAT), Literature of the Latin American and Caribbean Health Sciences (LILACS), and Scopus. Two authors performed study selection and data extraction. Multivariable mixed models were constructed for Cohen D of Eczema Area and Severity Index (EASI), SCORing Atopic Dermatitis (SCORAD), numeric rating scale (NRS)–itch and visual analog scale (VAS)–itch, and Dermatology Life Quality Index (DLQI). Overall, 64 trials were included. Use of concomitant topical therapy prescriptions, study duration ≥3 months, and fewer treatment arms were associated with an increased placebo response for EASI, NRS- and VAS-itch, and DLQI. For EASI, the placebo response was increased in studies with a higher proportion of male patients, mild-moderate mean baseline EASI scores, and no blinding. For NRS-itch, and VRS-itch, higher placebo responses were associated with higher proportions of male patients and moderate-severe mean itch scores at baseline. Placebo responses can be reduced in clinical trials of systemic therapy in AD by incorporating double- and triple-blinding, balancing the sex distribution of patients, disallowing concomitant use of prescription topical therapy, and having shorter study durations.