Effects of therapeutic doses of lactulose vs. polyethylene glycol on isotopic colonic transit

BACKGROUND: Lactulose and polyethylene glycol are osmotic agents used to treat idiopathic chronic constipation. AIM: To compare the effects of low doses of lactulose and PEG 4000 on transit time measured by scintigraphy in normal subjects. METHODS: For 5 days, 10 healthy subjects received either 10 g b.d. of lactulose or PEG 4000 in a randomized, double-blind, crossover study. On the evening of day 4, they took a capsule containing Amberlite resin pellets labelled with (111)In. On day 5, after a 1000 kcal test meal labelled with 99 Tcm, gastric, small bowel and colonic transits were measured. RESULTS: Gastric emptying and small bowel transit time were not different. Ascending colon emptying curve was significantly accelerated with lactulose in comparison with polyethylene glycol (P = 0.001) and, respectively, 50 +/- 18% vs. 35 +/- 18% of the radioactivity had left the ascending colon at the end of the study (P < 0.05). The descending colon filling curves, variations in the geometric centre and numbers of scintigraphic movements were not different. CONCLUSIONS: In healthy subjects, in comparison to PEG 4000, usual therapeutic doses of lactulose significantly accelerate ascending colon emptying. This result supports a stimulating motor effect of colonic fermentation of lactulose.