Colonoscopy: Understanding bowel preparation products

A colonoscopy is a test where a health professional examines the colon (also often referred to as the large intestine or the large bowel). A colonoscope is a thin, flexible telescope that is around the same thickness as a little finger. It is passed through the anus and into the colon, and can be pushed all the way round the colon as far as the caecum (where the small and large intestine meet). It contains fibre-optic channels which allow light to shine down so the operator can see inside your colon and it also has a 'side channel' down which devices can pass. These can be manipulated by the operator: for example, they may wish to take a small sample (biopsy) from the inside lining of the colon by using a thin 'grabbing' instrument which is passed down a side channel.

Who has a colonoscopy?

A colonoscopy is often recommended for individuals who are bleeding from the anus, are experiencing pain in their lower abdomen or have persistent diarrhoea.

A colonoscopy may confirm or rule out a number of illnesses such as cancer of the colon, polyps of the colon, Crohn’s disease, diverticula, or ulcerative colitis.

How is the bowel prepared for a colonoscopy?

In order for the operator of the colonoscope to have a clear view of the bowel, it must be empty. As such, all patients going through the procedure must follow a special diet and take a laxative before the test takes place. The recommended diet is low-residue, designed to reduce the amount of fibre in the body to minimize the amount of solid waste in the colon and rectum.

What products are available for bowel preparation?

The two major classes of bowel preparation are polyethylene glycol solutions and sodium phosphate preparations. Both are taken as an oral solution, with patients often given the solution in powder form and asked to take it within the 48 hours before the colonoscopy commences. Taking a bowel preparation laxative can cause a number of different side effects such as dizziness, headaches and feeling light headed, as well as significant diarrhoea. As such, patients are asked to remain close to a toilet throughout the period in which they are taking a preparation, as well as the 24hrs following the examination when leakage/excessive gas is also common.

Does any safety data exist for these products?

There are a number of systematic reviews of bowel preparation products, primarily concerned with their safety, efficacy, and tolerability. Many of these studies were undertaken in response to poor uptake of colonoscopy screening, with many patients stating that going through the process of preparing their bowels as one of the most significant deterrents for going ahead with the procedure.  

A systematic review undertaken in 2006, reviewing patient tolerance of polyethylene glycol and sodium phosphate preparations, found there to be no significant differences in efficacy although sodium phosphate was better tolerated in the 82 studies that were considered for analysis. The review also considered the tolerability of sodium picosulphate/magnesium citrate, another commonly prescribed preparation, although no clear benefits compared to other treatment preparations was established. Whilst sodium phosphate is better tolerated, a number of case series have highlighted that in a number of comparative studies it is also associated with the highest risk of clinically significant electrolyte disturbances. The systematic review was quick to highlight the methodological weaknesses of many of the studies that it used to draw conclusion, and stated that better study design and the introduction of new solutions that combined both better efficacy and tolerability would be crucial for allowing accurate future comparisons to be made.

Another systematic review, carried out by a group of gastroenterologists in the United States in 2004, investigated the relationship between low quality bowel preparation and its relationship with polyp detection rate (also known as adenoma detection rate). The study found that detection rates were not significantly different between intermediate-quality and high-quality bowel preparation, although low-dose bowel preparations often resulted in the need for repeat colonoscopies due to an inability to adequately view and detect all polyps >5mm. The study highlights the importance of both the type of bowel preparation used and patient adherence throughout the preparation process.

Further studies investigating other preparatory techniques, such as dietary modifications, have largely found them to be inadequate on their own for the purposes of colonoscopy but they are a beneficial adjunct to laxatives and improve the likelihood of an effective high-quality preparation.

Many of the systematic reviews, whilst considering the comparative benefits of each preparation, also stress the importance of understanding individual patient capabilities and tolerance levels when selecting the most appropriate colonic cleansing agent.

Is any medication or preparation administered after a colonoscopy? 

There are not usually any medicines taken after a colonoscopy, although occasionally some painkillers may be recommended by your health professional if you continue to feel certain discomfort. As excessive bowel movements are quite common after a colonoscopy, some patients are also advised to use petroleum jelly or similar barrier/lubricant around their anus if they are experiencing significant soreness in the area.

References

1. Trevisani L, Zelante A, Sartori S (2014) Colonoscopy, pain and fears: Is it an indissoluble trinomial? World J Gastro Endosc 16:6(6):227-33
2. Belsey J, Epstein O, Heresbach D (2006) Systematic review: oral bowel preparation for colonoscopy Ali Pharm Thera 15:25(4):373-84
3. Ainley EJ, Winwood PJ, Begley JP (2005) Measurement of serum electrolytes and phosphate after sodium phosphate colonoscopy bowel preparation: an evaluation Dig Dis Sci 50(7):1319-23
4. Clark BT, Rustagi T, Laine L (2014) What level of bowel prep quality requires early repeat colonoscopy: systematic review and meta-analysis of the impact of preparation quality on adenoma detection rate Am J Gastroenterol 109(11):1714-23
5. Lim YJ, Hong SJ (2014) What is the best strategy for successful bowel preparation under special conditions? World J Gastroenterol 21:20(11):2741-5