Clinical Question: Is polyethylene glycol (PEG) 3350 or lactulose a better treatment for children with functional constipation?

Setting: Outpatient (specialty)

Study Design: Randomized controlled trial (double-blinded)

Allocation: Concealed

Synopsis: In this study, investigators compared two osmotic laxatives, lactulose and PEG 3350, in children six months to 15 years of age who met two of the following four criteria: (1) fewer than three bowel movements per week; (2) encopresis more than once a week; (3) large amounts of stool (enough to clog the toilet) every one to four weeks; and (4) palpable abdominal or rectal mass. Children with an organic cause for constipation, such as Hirschsprung’s disease, were excluded.

Before randomization, all children underwent an untreated one-week run-in period, during which symptoms were recorded and use of oral laxatives was not allowed. They received one enema per day for three days at the end of the week to clear any stool in the rectum. Children six months to six years of age were randomly assigned to receive 6 g of lactulose or 2.95 g of PEG 3350 per day; children six to 15 years of age received 12 g of lactulose or 5.9 g of PEG 3350 per day. After one week, treatment effect was assessed. The dosage was increased by one dose per day if symptoms persisted or was cut in half if the child was having diarrhea. A stimulant laxative also was given if the symptoms had not improved from baseline.

Patients were evaluated again at two, four, and eight weeks, at which time the dosage could be adjusted. The primary outcome, evaluated using per-protocol analysis, was treatment success at eight weeks, defined as at least three bowel movements per week and encopresis no more than once every two weeks. Although per-protocol analysis is less robust than intention-to-treat analysis, in this case only four of 50 patients in the PEG 3350 group and five of 50 patients in the lactulose group withdrew prematurely, making bias unlikely.

At the end of the eight-week study, the frequency of stools increased similarly in both groups from fewer than three to approximately seven per week. The frequency of encopresis decreased from more than once per day at intake to approximately three times per week in both groups. The end point of treatment success was achieved more often in the PEG 3350 group (56 versus 29 percent;P = .02; number needed to treat = four). Treatment was successful more often in girls, in children with less than one year of symptoms before enrollment, and in those with less encopresis at enrollment. PEG 3350 was somewhat better tolerated than lactulose in regard to side effects such as abdominal pain, pain at defecation, and straining at defecation, but children disliked the taste of PEG 3350 more than the taste of lactulose.

Bottom Line: PEG 3350 and lactulose increase stool frequency and decrease encopresis in children with functional constipation. Overall treatment success (using a somewhat arbitrary measure defined by the researchers) was more likely in the PEG 3350 group and, other than its taste, PEG 3350 was somewhat better tolerated than lactulose. (Level of Evidence: 1b)