A new approach to characterize whole-gut transit in infants with use of a nonabsorbable intestinal marker.

To characterize mouth to anus transit of intestinal contents, polyethylene glycol (PEG) was given as an intestinal marker to 11 healthy infants, and daily fecal collections were analyzed for PEG concentration per unit of dry stool weight for 9-15 d. Fecal PEG excretion followed first-order kinetics. Thus, half-life (t1/2) and volume of distribution (Vd) of PEG in the gut could be computed for each of seven infants who received continuous daily PEG doses and t1/2 only for four infants who received a single PEG dose. t1/2 of PEG in the gut was 0.99 +/- 0.48 d (means +/- SD). Vd for PEG in the gut was 18.74 +/- 15.38 g of fecal dry weight. We propose that whole-gut transit be expressed in terms of t1/2 and Vd of intestinal contents because these may better characterize the changes in intestinal transit that occur with disease or dietary modifications.