A comparison of bowel preparations for flexible sigmoidoscopy: oral magnesium citrate combined with oral bisacodyl, one hypertonic phosphate enema, or two hypertonic phosphate enemas

Am J Gastroenterol. 1999 Aug;94(8):2122-7. doi: 10.1111/j.1572-0241.1999.01308.x.


Objective: Magnesium citrate with hypertonic enemas or oral bisacodyl provides superior preparation quality for sigmoidoscopy over enemas alone. We compared three magnesium citrate sigmoidoscopy preparations in a randomized, single-blind, controlled trial.

Methods: Two hundred and ninety-one adults scheduled for routine sigmoidoscopy were randomly assigned to receive one of three preparations containing oral magnesium citrate (296 cc) taken the night before the procedure in combination with the following: 1) oral bisacodyl (10 mg), given with the magnesium citrate the night before the procedure; 2) one hypertonic phosphate enema 1 h before the procedure; or 3) two hypertonic phosphate enemas, given singly at 2 and 1 h before the procedure. Endoscopists rated preparation quality, procedure duration, and depth of endoscopic insertion. Patients assessed preparation comfort and overall satisfaction.

Results: Preparation quality was rated as excellent or good for 80.6% in the bisacodyl group, 88.7% in the one-enema group, and 85.1% in the two-enema group (p = 0.30). Patients reported the oral bisacodyl regimen was better tolerated (p = 0.032). Although the three regimens were comparable in most side effects, the bisacodyl preparation was associated with more diarrhea (p = 0.0003). Mean procedure duration, mean insertion depth, and prevalence of diverticula and polyps were similar in all groups. Fewer than 4% of patients required repeat procedures due to poor preparation quality.

Conclusions: There was no statistical difference between the quality of the three bowel preparations. Patients considered an oral bisacodyl and magnesium citrate regimen more easily tolerated, though it was associated with more diarrhea.

Publication types

  • Clinical Trial
  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Administration, Oral
  • Adult
  • Aged
  • Bisacodyl / administration & dosage*
  • Cathartics*
  • Citric Acid / administration & dosage*
  • Colonic Polyps / diagnosis
  • Female
  • Humans
  • Male
  • Middle Aged
  • Organometallic Compounds / administration & dosage*
  • Phosphates / administration & dosage*
  • Sigmoidoscopy*
  • Single-Blind Method


  • Cathartics
  • Organometallic Compounds
  • Phosphates
  • Bisacodyl
  • Citric Acid
  • magnesium citrate
  • sodium phosphate