What is the role of laxatives in IBS?
When constipation associated with IBS does not improve with fiber, low-dose laxatives can improve bowel function. Osmotic laxatives should be tried first as they tend to be gentler and cause fewer side effects such as cramps and diarrhea. Although effective at improving bowel function, osmotic laxatives such as polyethylene glycol do not improve abdominal symptoms, including abdominal pain. In a recent study, patients with IBS-C were randomized to either polyethylene glycol or placebo for 28 days. Although both groups showed an increase in the mean weekly number of spontaneous bowel movements (SBMs) from baseline, the polyethylene glycol group had a statistically significant improvement (4.40 ± 2.581) as compared with placebo (3.11 ± 1.937). However, there was no difference in abdominal discomfort or pain with polyethylene glycol as compared with placebo.
It should be remembered that patients with constipation should be evaluated for pelvic floor dyssynergia, because many of these patients may respond to biofeedback therapy, a technique that retrains patients to relax their pelvic floor muscles when attempting defecation.