Small Molecules in the Treatment of Acute Severe Ulcerative Colitis: A Review of Current Evidence.

Ulcerative colitis (UC) is an inflammatory bowel disease in which one-quarter of patients are at risk of developing a severe form of the disease known as acute severe UC (ASUC). This condition exposes patients to serious complications, including toxic megacolon, surgical intervention, and even death. The current therapeutic strategy relies on time-dependent, multi-step algorithms that integrate systemic corticosteroids, calcineurin inhibitors, and biologic agents (specifically infliximab) as medical therapy aimed at avoiding colectomy. Despite this approach, a significant proportion of patients fail to respond to either corticosteroids or infliximab and may require alternative therapeutic options if there is no urgent surgical necessity. These alternatives include other biologics or emerging small molecules, although the evidence supporting these treatments remains extremely low, even considering their well-documented and promising efficacy and safety in moderate-to-severe UC. Conversely, it is necessary to investigate whether infliximab can be effectively replaced or surpassed by other approved biological agents and small molecules as first-line therapy after steroid resistance. This review aims to summarise the available evidence on small molecules, specifically Janus kinase inhibitors and sphingosine-1-phosphate receptor modulators.