Colonoscopy is one of the most common procedures performed by gastroenterologists, and adequate bowel preparation is paramount to improving patient outcomes. However, patients often hesitate to undergo colonoscopy because of concerns that they will not be able to tolerate the taste or the volume of the bowel preparation, which can be up to 4 liters for some formulations.

Importance of Adequate Bowel Prep

From the perspective of the gastroenterologist, adequate bowel prep is crucial in screening colonoscopy, for which it is used to detect cancerous and precancerous lesions, and in diagnostic colonoscopy, such as that performed because of bleeding or diarrhea. Up to 25% of patients undergoing colonoscopy may have an inadequate prep, which may lead to missed lesions, longer procedure times, and an increased risk of complications.1

When comparing inpatients with outpatients, inadequate prep typically occurs more frequently in hospitalized patients, which can lead to a delay in diagnosis, increased hospital costs, and an extended length of stay for these patients.2 Regardless of patient setting, inadequate prep also affects quality indicators for gastroenterologists, including adenoma detection rate and cecal intubation rate, which are directly associated with patient outcomes and are increasingly tied to overall costs and reimbursement.2

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Risk Factors for Inadequate Prep

Several risk factors for inadequate prep are important to identify in patients undergoing colonoscopy. These include prior inadequate prep, chronic constipation, chronic opioid use, male sex, increased body mass index (BMI), cirrhosis, history of Parkinson disease or diabetes, and positive fecal occult blood test (FOBT).3,4 Some gastroenterologists will choose to have these at-risk patients follow a split-dose or same-day-dose bowel preparation to help improve the quality of the prep.4

When evaluating a patient for colonoscopy, a thorough medication reconciliation should always be completed. Specifically, medications that may slow colonic motility (eg, opioids, anticholinergics) or indicate a history of some of the risk factors noted above should be identified and addressed in advance of the colonoscopy.

New Formulation Needed

Because of the significant impact bowel preparation for colonoscopy has on patients and gastroenterologists, developing medications or methods to improve its adequacy is an area of great research interest. Patients often ask their gastroenterologist if there is a tablet version of the prep because of their previous experiences or what they have heard about large-volume preparations. With few tablet-only preps available, some patients may defer undergoing a colonoscopy.

Recently, a new oral sulfate tablet (OST) formulation was developed and approved by the US Food and Drug Administration (FDA) for use in colonoscopy preparation.5 A key study supporting this approval was recently published by Di Palma and colleagues in the American Journal of Gastroenterology.6  

This new OST formulation contains sodium and magnesium sulfate salts with potassium chloride. The patient must ingest 24 tablets, with an expected output of about 3 liters of diarrhea. In this study, the OST formulation was compared with a traditional polyethylene glycol with ascorbate preparation (PEG-EA), both of which were given using a split-dosing regimen. Patients receiving OSTs were required to consume a fair amount of liquid, with each 12-tablet dose taken with a minimum of 16 ounces of water followed by an additional 32 ounces with each dose.

Study Results

Physicians performing the colonoscopies were blinded to patients’ prep and scored each colon segment (proximal, mid, distal) on a 4-point scale: excellent, good, fair, or poor. Excellent and good were considered successful while fair and poor were considered failures.

A total of 548 patients were included from 22 study centers within the United States in the final statistical analysis. It is important to note that this was a noninferiority study. The OST group had similar rates of success (92.4%) when compared with PEG-EA (89.3%). The OST group did have significantly higher rates of excellent preps when compared to PEG-EA (66.2% vs 57.0%; P =.034).

In general, there was no statistically significant difference in prep scores between the OST and PEG-EA groups in each segment (proximal, mid, and distal). However, there were more excellent preps in the proximal colon segment with OST compared with PEG-EA (63.7% vs 55.1%; P =.034). This statistically significant difference was not observed in the mid and distal colon where the rates of excellent prep were not statistically significantly different. 

Positive Outcomes

From a quality indicator standpoint, there was no statistically significant difference in secondary procedure outcomes such as adenoma detection rate or cecal intubation rate and procedure duration between the 2 groups. Patients who were considered “hard to prep” (eg, prior failed colonoscopy, opioid use, history of constipation, and BMI ≥35) had similar rates of prep efficacy between groups (OST, 89.6% vs PEG-EA, 82.7%).

A similar number of patients in each group reported adverse events (OST, 27.4% vs PEG-EA, 27.7%; P =NS). There were no statistically significant differences between the groups in any type of unsolicited adverse event (eg, gastrointestinal, infectious). However, patients in the PEG-EA group were more likely to report no nausea and vomiting compared with OST for solicited symptoms. Any differences between the groups in laboratory abnormalities were considered mild and clinically insignificant by the authors.

Patients were also asked to complete a preference questionnaire, which demonstrated that those using the OST prep had a significantly better experience consuming the prep as well as overall experience. This result was based on the OST prep being more likely to be rated as easy or very easy to complete. The authors concluded that OST was noninferior to PEG-EA and had significantly more excellent preps, including of the proximal colon.

Limitations and Warnings

Unfortunately this study did not use a bowel preparation scale such as the Boston Bowel Preparation Scale (BBPS), which has become a more standardized scale used in the literature. Using the BBPS might have made the results more generalizable to both past and future studies. Also, the prep preference questionnaire used in this study has not been formally validated.

This new OST prep should not be confused with a previously available prep using a sodium phosphate-based prep that was associated with excessive phosphate absorption and nephrocalcinosis.7 It had a higher tablet burden of between 32 and 40 tablets. This prep is rarely used anymore based on these potential adverse events and carries an FDA black box warning for permanent impairment of renal function.7

This degree of renal dysfunction was not reported in the OST study and would hypothetically be less likely based on its components. If OST becomes routinely used, it will be important to collect postmarketing data to determine if any serious renal dysfunction is observed in patients.

Tips for Success

When evaluating a patient for a colonoscopy, it is critical to have screening questions aimed at identifying patients at high risk for an inadequate prep. These types of questionnaires are especially important when evaluating patients for direct-access colonoscopies, in which formal preprocedural visits may be bypassed.

In addition to using a split-dosing regimen, prep tolerance can also be improved by pretreating patients with antiemetics such as ondansetron, chilling the prep for several hours before starting, using flavorings (but not red or purple ones, which can be mistaken for blood), and using a low-residue (low-fiber) diet for several days leading up to the colonoscopy.

Regardless of the type of bowel prep used for colonoscopy, education and patient navigation throughout the process cannot be overemphasized.8 Many practices are using apps and/or videos that can be downloaded by patients and reviewed before their procedure.

Finally, although the new OST preparation may sound exciting to patients, it is important to emphasize that a relatively large amount of liquid must still be ingested.


1. Harewood GC, Sharma VK, de Garmo P. Impact of colonoscopy preparation quality on detection of suspected colonic neoplasia. Gastrointest Endosc. 2003;58(1):76-79. doi:10.1067/mge.2003.294

2. Rex DK, Imperiale TF, Latinovich DR, Bratcher LL. Impact of bowel preparation on efficiency and cost of colonoscopy. Am J Gastroenterol. 2002;97(7):1696-1700. doi:10.1111/j.1572-0241.2002.05827.x

3. Hassan C, Fuccio L, Bruno M, et al. A predictive model identifies patients most likely to have inadequate bowel preparation for colonoscopy. Clin Gastroenterol Hepatol. 2012;10(5):501-506. doi:10.1016/j.cgh.2011.12.037

4. Rex DK. Optimal bowel preparation–a practical guide for clinicians. Nat Rev Gastroenterol Hepatol. 2014;11(7):419-425. doi:10.1038/nrgastro.2014.35

5. Sutab® (sodium sulfate, magnesium sulfate, and potassium chloride) tablets. [Highlights of prescribing information.] Holbrook, MA: Braintree Laboratories; 2020.

6. Di Palma JA, Bhandari R, Cleveland MV, et al. A safety and efficacy comparison of a new sulfate-based tablet bowel preparation versus a PEG and ascorbate comparator in adult subjects undergoing colonoscopy. Am J Gastroenterol. Published online November 6, 2020. doi:10.14309/ajg.0000000000001020

7. Osmoprep (sodium phosphate monobasic monohydrate and sodium phosphate dibasic anhydrous) tablets. [Highlights of prescribing information.] Bridgewater, NJ: Salix Pharmaceuticals; 2018.

8. Millien VO, Mansour NM. Bowel preparation for colonoscopy in 2020: a look at the past, present and future. Curr Gastroenterol Rep. 2020;22(6):28. doi:10.1007/s11894-020-00764-4.