An in vitro and clinical dose-finding study of antifoaming effects of simethicone during colonoscopy

Simethicone is an antifoaming agent frequently added to endoscopic rinse solutions but has recently been implicated as a risk factor for transmission of infections due to the formation of simethicone deposits within scope channels. Since the build-up of residue is likely dose-related, the smallest effective dose of simethicone should be used but there are no data available on the effective dose. Thus, we conducted a dose-finding study in an "in vitro bubble model" to determine the appropriate simethicone dose. Six 100-mL test tubes were filled with a 1% (v/v) solution of kitchen detergent (Fairy®, Procter & Gamble, London, England) in water for irrigation (Baxter®, Sydney, Australia). One test tube served as the control, while different doses of simethicone (Infacol®, Nice Pak, Melbourne, Australia) were added to the other five tubes (0.02, 0.2, 2.0, 20, and 200 mg/100 mL). Oxygen was streamed for 30 s into the test tubes at a rate of 2 L/min. After 10 s, photographs were taken and the visible bubbles were semi-quantitatively rated by independent assessors blinded to the dosing of simethicone. Simethicone at doses of 2 mg/100 mL had no appreciable antifoaming effect, whereas concentrations ≥ 20 mg/100 mL were sufficient to suppress bubble formation. This is substantially lower compared with frequently used doses of up to 200 mg/100 mL. Subsequently, we tested the lower simethicone dose with previously used higher doses, in 1475 and 1340 patients, respectively. We found it to have no impact on polyp detection with a rate of 56.7% (54.2-59.3% [95% CI]) at the lower dose and 56.5% (53.8-59.1% [95% CI]) at the higher dose.