Quantitative, noninvasive assessment of antidiarrheal actions of codeine using an experimental model of diarrhea in man.

Enteric coating of a capsule has been used to deliver a bolus of radioisotope to the ileocecal region. This has allowed quantitative assessment of regional colonic transit in a group of healthy subjects whose proximal colonic transit was accelerated by lactulose 20 ml thrice daily. In this experimental model of diarrhea, codeine delayed transit from mouth to terminal ileum and also delayed transit through the ascending colon from 5.3 +/- 2.5 hr to 7.4 +/- 2.5 hr, N = 11, P < 0.05. Furthermore, codeine delayed whole colon transit, as assessed by geometric center analysis, which showed the delay to be most marked in the right colon with little effect noted in the left colon. In addition, codeine significantly reduced the number of retrograde movements observed and reduced the colonic response to eating. The antidiarrheal effect of codeine appears to be due to a combination of delayed mouth-cecum transit plus an additional delay in the ascending colon. This colonic delay may be partially explained by a reduction in postprandial propulsive movements that were seen in this model of diarrhea.