DiPalma, J.A., Cleveland, M.B., McGowan, J., & Herrera, J.L. (2007b). A randomized, multi-centered, placebo-controlled trial of polyethylene glycol laxative for chronic treatment of chronic constipation. American Journal of Gastroenterology, 102, 1436–1441.

To compare the safety and efficacy of polyethylene glycol (PEG) versus placebo over a six-month treatment period in patients with chronic constipation.

PEG 3350 (Miralax^®) laxative 17 g or placebo was administered daily for six months. Patients were randomly assigned in a 2:1 ratio to PEG or placebo. This was a subjects mixed study. Medication was administered in 8 oz of juice or another beverage. Bisacodyl 10 mg (5 mg tablets) was used as rescue medication for severe discomfort related to constipation. Fiber was prohibited. Other nonconstipating medications were allowed.

• The study reported on a sample of 204 patients in the treatment group and 100 patients in the placebo group.
• Mean patient age was 53 years (range 20 to 92).
• The older adult subgroup comprised patients aged 65 years or older (n = 75).
• The sample comprised 258 women (85%).
• The sample was 84% Caucasian, 13% African American, and 3% Hispanic or Latino.
• Average duration of constipation was 23 years.
• Patients were included in the study if they had a three-month history of fewer than three bowel movements (BMs) per week when not taking laxatives and one or more remaining Rome symptom criteria. Patients also had an average of three or fewer satisfactory BMs per week during the 14-day observational period after eligibility criteria were met.
• Patients were excluded if they had loose stools, sufficient criteria for irritable bowel syndrome, and currently were being or previously had been treated with PEG.

50 centers in the United States

This was a double-blind, placebo-controlled, parallel, randomized controlled trial.

• During the 14-day observational period and qualification period, baseline constipation status was confirmed.
• During the treatment period, data were collected through an interactive voice response system daily to record BM experiences. Patients answered daily and weekly questions (e.g., number of BMs, straining, lumpy or hard stools, evacuation complete, satisfaction, cramping) on a Likert-type scale from 0 (none) to 4 (extreme).
• Amount of gas was rated on a Likert-type scale from 0 (no gas) to 4 (extreme gas).

• Of 609 patients screened, 300 did not meet criteria or failed the 14-day observational period. Of the remaining patients, 306 enrolled and were randomized, and 2 were excluded. A total of 175 patients completed the study.
• Primary analysis was based on intention to treat (ITT).
• Efficacy of the primary variable, treatment success, was defined as relief of modified Rome criteria for constipation for 50% or more of a patient's treatment weeks. The PEG group achieved significant benefit (p < 0.001) versus placebo in 11 of 12 primary and secondary measures.
• The total sample had a 41% difference in treatment response (52% in the PEG group versus 11% in the placebo group, p < 0.001).
• The older adult group had a 46% difference favoring PEG.
• The treatment group had more total BMs per week.
• Total compliance with study medication was higher than 86%.
• Patient withdrawal was equivalent for each reason category, except lack of efficacy; twice as many patients in the placebo group withdrew secondary to lack of efficacy.

PEG is safe and effective in management of constipation in adults and older adults for up to six months.

The study focused on chronic constipation and lacked focus on cancer or opioid-induced constipation.