Low-volume oral colonoscopy bowel preparation: sodium phosphate and magnesium citrate

Low-volume oral colonoscopy preparations are easier to tolerate and are gaining popularity at the expense of large-volume lavage solutions. The aims of this two-part study were to compare two oral colonoscopy bowel preparations, sodium phosphate (NaP) and magnesium citrate (Mg), and to assess the effects of timing and dilution of NaP.

Part 1 included 300 ambulatory patients randomized to receive NaP or Mg on the day before colonoscopy. Patients completed a questionnaire before colonoscopy. The endoscopist, blinded to the type of bowel preparation, rated bowel cleansing and recorded the presence of any rectosigmoid aphthous ulcers. In part 2, a total of 297 patients received NaP diluted into 3 doses 10 minutes apart the evening before and the morning of the day of colonoscopy. This group was compared with the group in part 1 that received NaP in two separate single doses entirely the day before colonoscopy.

NaP and Mg were well tolerated. When preparations were taken the day before colonoscopy, Mg achieved better bowel cleansing (p < 0.001). Taking NaP entirely the day before colonoscopy resulted in poor right colon cleansing (27%). In contrast, taking NaP the evening before and morning of colonoscopy improved cleansing in the right colon (p < 0.001). Vomiting occurred less frequently with dilution of NaP. Rectosigmoid aphthous ulcers occurred more often with NaP (5.5%) than Mg (1%), p < 0.01. For patients who, according to questionnaire, had received a previous bowel preparation, NaP and Mg were both preferred over large-volume lavage solutions, whereas NaP was preferred over Mg.

When taken entirely the day before colonoscopy, Mg is superior to NaP. Taking NaP the evening before and morning of colonoscopy improved bowel cleansing compared with taking it entirely the day before. Dilution of NaP reduces vomiting. NaP induces rectosigmoid aphthous ulcers more often than Mg.