A Prospective Audit of Tolerability, Mucosal Cleansing Efficacy and Mucosal Abnormalities Associated With Standard Orally Administered Colon Cleansing Preparations for Colonoscopy

There are several published trials of different colon cleansing agents for colonoscopy (which is the investigation of choice for visualisation of the colonic mucosa) which compare different regimens. However, a recent published meta-analysis has shown that most audits and studies were underpowered with poor study design and so no consensus on the most effective preparation exists1. 10-20% of failed colonoscopy is attributable to inadequate bowel cleansing which has a negative impact on the detection of potential malignant lesions in the colon3 as well as requiring the patient to attend again for further colonoscopy after repeated colon cleansing which also impacts on waiting lists and healthcare costs.

Colon cleansing preparations can be broadly classified into three groups. Osmotic laxatives such as sodium phosphate (NaP) increase colon water content by attracting extracellular fluid efflux through the bowel wall. Polyethylene glycol (PEG) laxatives are high molecular weight non-absorbable polymers that are administered in a dilute electrolyte solution, this is retained in the colon where it acts as a bowel cleanser without any significant fluid exchange across the colonic mucosa. The third group are stimulant laxatives such as senna or sodium picosulphate which work primarily by enhancing smooth muscle contractility and also they may increase bowel water content.

Previous published audits and studies comparing different types of colon cleansing preparations have been limited by small sample size with only 5 published papers having over 100 patients in each arm of the study. These 5 studies suggest that NaP may be better than PEG but the recent meta-analysis failed to show this, primarily due to the large number of smaller studies showing PEG was better than NaP. Interpretation of the studies is limited by inconsistent and poorly defined measures of efficacy outcome. Most studies have used a subjective endoscopists assessment of the overall quality of the bowel preparation making comparisons between studies impossible. Recently a calibrated externally validated outcome assessment tool has been developed to objectively quantify the quality of bowel preparation4, but no randomised published study has yet utilised this tool.

In the absence of clear difference in efficacy between preparations then patient tolerability is likely to be an important distinguishing feature when selecting a treatment. Data on tolerability outcomes is limited but there is some evidence that PEG solutions are less well tolerated due to the volume of liquid required to drink. This is an area where further study is needed.

The ability of a colonic cleansing preparation to clean the colon effectively also must be balanced by its ability to not induce changes in the lining of the bowel itself. Ulceration and inflammation of the colon has been shown to occur in 3-24% of patients using NaP compared with 1-2% in those receiving PEG. Such findings can be mistaken for inflammatory bowel disease such as Crohns or put down to drug induced changes such as non steroidal anti inflammatory agents (NSAIDs). However, these studies have been either non randomised5 or underpowered to detect real differences.