Regulatory requirements for claims of mucosal healing in ulcerative colitis (UC) will require demonstration of both endoscopic and histologic healing. 

Quantifying these rates is essential for future drug development.

Dr Jairath and colleagues from Canada reviewed endoscopic and histologic placebo response and remission rates in UC randomised controlled trials, and identified factors influencing these rates.

MEDLINE, EMBASE and the Cochrane Library were searched from inception to 2017 for placebo‐controlled trials of pharmacological interventions for UC. 

Endoscopic and histologic placebo rates were pooled by random effects. 

The research team included 56 induction, and 8 maintenance trials. 

Pooled placebo endoscopic remission and response rates for induction trials were 23%, and 35% respectively, and 20% for maintenance of remission. 

The pooled histologic placebo remission rate was 14% for induction trials. 

The researchers observed high heterogeneity for all outcomes. 

On multivariable meta‐regression, central endoscopy reading was associated with significantly lower endoscopic placebo remission rates. 

On univariable meta‐regression, the team observed that a higher histologic placebo remission was associated with concomitant corticosteroids.

Dr Jairath's team comments, "Placebo endoscopic and histologic rates range from 14% to 35% in UC randomized controlled trials but are highly heterogeneous."

"Outcome standardization may reduce heterogeneity and is needed in this field."