Impact of Timing of Premedication on Mucosal Visibility During Endoscopy: A Randomized Controlled Trial

BACKGROUND: Adequate gastric mucosal visibility (GMV) is essential for high quality upper gastrointestinal (GI) endoscopy. Simethicone and N-acetylcysteine (NAC) are commonly used to improve mucosal visibility, but the optimal timing of administration remains uncertain. OBJECTIVE: This double-blinded randomized controlled trial (RCT) evaluated the optimal interval between premedication (simethicone + NAC) and endoscopy for achieving adequate GMV. DESIGN: In this RCT, adults undergoing elective upper GI endoscopy were randomized to four groups: placebo (Group 1), premedication to endoscopy interval of 10-20 (Group 2), 21-30 (Group 3), or > 30 min (Group 4). GMV was scored in four gastric regions (antrum, distal body, proximal body, fundus) on a 4-point scale (range 4-16). The primary outcome was adequate GMV (total score < 7). Secondary outcomes included median total GMV score, region-wise mucosal visibility scores, lesion detection rate, and predictors of adequate GMV. RESULTS: A total of 1200 adults were randomized to four groups. Adequate GMV was significantly more frequent in Groups 3 (64.7%) and 4 (66.7%) than in placebo (2.7%) or Group 2 (25.0%). Subgroup analysis within Group 4 demonstrated a declining trend after 50 min. ROC analysis suggested an optimal cut-off of 25 min in predicting adequate GMV with area under the curve of 0.80. In region-wise analysis, mean visibility scores were lowest in antrum and distal body. There was no significant difference in the detection of gastric lesions across study groups (p = 0.913). No serious adverse events related to premedication were observed. CONCLUSION: Premedication with simethicone and NAC significantly improves GMV. The improvement becomes optimal at 20-30 min after ingestion and is consistently maintained up to 50 min. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT06581783.