Shortened preparative fasting before contrast-enhanced CT and acute adverse drug reactions: A real-world observational study of 242,435 examinations.

OBJECTIVES: Although routine fasting before contrast-enhanced CT (CECT) is no longer recommended, evidence remains limited and fasting is still common in practice. We evaluated whether shortened preparatory fasting before CECT affects the incidence of acute iodinated contrast media (ICM)-related adverse drug reactions (ADRs). METHODS: This retrospective observational study included adults who underwent CECT during January-July 2023 (long nil per os [NPO]: 6-h fasting from solids and liquids) and January-July 2024 (short NPO: 3-h fasting from solids with no liquid restriction). Acute ADR incidence was analyzed in all patients, a dual-period cohort (patients undergoing CECT in both periods), and a single-period cohort (patients undergoing CECT in only one period). After inverse probability of treatment weighting, adjusted risk ratios (RRs) for overall and specific acute ADRs (hypersensitivity, physiologic, and emetic reactions) were estimated using log-binomial regression with generalized estimating equations. Aspiration pneumonia incidence was also assessed. RESULTS: A total of 98,519 patients (118,976 examinations) in the long-NPO period and 98,739 patients (123,459 examinations) in the short-NPO period were included. Per-patient ADR incidence was 1.2 % and 1.3 %, respectively. Shortened fasting was not associated with an increased risk of overall ADRs (adjusted RR, 1.04; 95 % CI: 0.97, 1.13; P = 0.26) or hypersensitivity (adjusted RR, 1.03; 95 % CI: 0.94, 1.12), physiologic (adjusted RR, 1.05; 95 % CI: 0.89, 1.25), or emetic reactions (adjusted RR, 1.12; 95 % CI: 0.92, 1.37). No aspiration pneumonia occurred. CONCLUSION: Shortening preparatory fasting was not associated with a statistically detectable increase in acute ICM-related ADRs or aspiration pneumonia. As an observational before-after study, these findings support relaxation of fasting protocols but do not establish equivalence or non-inferiority.