Bowel Preparation for CT Colonography: Blinded Comparison of Magnesium Citrate and Sodium Phosphate for Catharsis 1

Department of Radiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Ave, G3/310 CSC MC 3252, Madison, WI 53792-3252, USA.
Radiology (Impact Factor: 6.87). 01/2010; 254(1):138-44. DOI: 10.1148/radiol.09090398
Source: PubMed


To compare colonic cleansing and fluid retention of double-dose magnesium citrate with those of single-dose sodium phosphate in patients undergoing computed tomographic (CT) colonography.
This retrospective HIPAA-compliant clinical study had institutional review board approval; informed consent was waived. The study included 118 consecutive patients given single-dose sodium phosphate for bowel catharsis and 115 consecutive patients at risk for phosphate nephropathy, who were instead given double-dose magnesium citrate. The bowel preparation regimen was otherwise identical. Four-point scales were used to assess residual stool and fluid in the six colonic segments, and attenuation of residual fluid was measured. An a priori power analysis was performed, and unpaired t tests with Welch correction were used to compare the two groups on stool and fluid scores and fluid attenuation.
Both cathartic regimens offered excellent colon cleansing, with no significant difference for residual stool in any of the six segments. Stool scores of 1 or 2 (ie, no residual stool or residual stool <5 mm) were recorded in 88.6% (627 of 708) of colonic segments in the sodium phosphate group and in 88.1% (608 of 690) in the magnesium citrate group. No clinically important differences were seen in residual fluid scores in any of the six segments, with the only significant difference seen in the sigmoid colon (2.17 for sodium phosphate vs 2.44 for magnesium citrate; P< 0.01). Fluid attenuation was significantly different between magnesium citrate and sodium phosphate groups (790 HU +/- 216 vs 978 HU +/- 160; P <.001).
Both sodium phosphate and magnesium citrate provided excellent colon cleansing for CT colonography. Residual stool and fluid were similar in both groups, and fluid attenuation values were closer to optimal in the magnesium citrate group. Since bowel preparation provided by both cathartics was comparable, magnesium citrate should be considered for CT colonography, particularly in patients at risk for phosphate nephropathy.

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    • "Likewise, in the CTC group, all false-positive patients (n = 2) and patients with poor bowel preparation (n = 3) had been prepared with magnesium citrate. Magnesium citrate has a less potent cathartic effect than sodium phosphate or PEG, and a double dose of magnesium citrate (592 mL) was required to achieve the same level of colon cleansing as 45 mL of sodium phosphate in one study (35). Nevertheless, we only used a moderate amount of magnesium citrate in our patients, since it should be used with caution in patients with renal impairment, even if it is safer than sodium phosphate, which should not be used in patients with decreased renal function (15, 36-39). "
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