US Pharm. 2013;38(12):30-34.
ABSTRACT: According to the U.S. Preventive Services Task Force,
endoscopic screening for colorectal cancer has the potential to save
thousands of lives each year. To maximize the diagnostic accuracy of a
colonoscopy, it is crucial that the patient be prepared for the
screening procedure. Two factors limiting the success of colonoscopy
preparations are patient compliance and tolerability. Bowel preparations
currently available for colonoscopy include compounds such as
polyethylene glycol and sodium phosphate. Despite the emergence of newer
alternatives, there is still no ideal preparation for colonoscopy.
Community pharmacists can educate patients, address their concerns, and
offer them individualized recommendations in order to improve the rates
of successful bowel cleansing for colonoscopy.
Colorectal cancer (CRC) is the second leading cause of cancer-related
deaths in the United States and the third most common cancer in both
men and women.1 The 5-year survival rate for patients whose
CRC is diagnosed early (stage I) is greater than 90%, supporting the
importance of early detection in reducing mortality.2
The U.S. Preventive Services Task Force has stated that endoscopic
screening for CRC can potentially save thousands of lives annually.3
It is essential, therefore, that patients be prepared for their
screening procedure in order to maximize its diagnostic accuracy.
According to the American Society for Gastrointestinal Endoscopy,
colonoscopy is considered the gold standard for CRC screening.4
Inadequate bowel cleansing is responsible for nearly one-third of
incomplete procedures, resulting in a reduced rate of polyp and adenoma
detection.5 The accuracy of colonoscopy results relies
heavily upon the selection of an appropriate bowel-preparation regimen,
along with strict adherence to administration. This review will address
the various bowel preparations used for colonoscopy and identify
strategies for improving patient compliance and tolerability, two
factors that limit the success of bowel preparations.
Traditional Bowel Preparations
Bowel preparations used for colonoscopy generally contain a
hyperosmotic, isosmotic, or stimulant, or a combination of these agents.
Factors that should be considered when a regimen is being selected
include coexisting conditions, concomitant medications, age, and patient
preference. The most commonly dispensed bowel preparations are
polyethylene glycol (PEG) and sodium phosphate (NaP). Poor tolerability
of these traditional agents has triggered the development of newer
agents, such as SUPREP, Suclear, and Prepopik.
PEG-Based Preparations: PEG-based preparations
are isosmotic, nonabsorbable electrolyte solutions that cleanse the
bowel through cathartic effects resulting from ingestion of a large
fluid volume. Several PEG-based preparations are available, each
differing in aspects such as dose volume, electrolyte content, and
flavor (e.g., GoLYTELY, Colyte, PEG-3350, NuLYTELY, Trilyte). Decreased
tolerance of, and compliance with, older PEG-based solutions is commonly
attributed to unpleasant taste. Newer sulfate-free, PEG-based products
(e.g., NuLYTELY, Trilyte) have been developed to improve palatability.6 In addition, standard PEG-based preparations are now available with flavor enhancers to improve tolerability.7
Tolerability and compliance are also influenced by the large volume
of fluid required for ingestion. For conventional dosing, traditional
PEG-based preparations should be reconstituted with water to 4 L and
consumed as 8 oz every 10 minutes until finished or rectal fluids are
clear.8 As an alternative, split dosing has successfully addressed volume-related challenges while improving efficacy (TABLE 1).9-13
Split-dose regimens generally recommend the ingestion of 2 L the
evening before colonoscopy, followed by 2 L the next morning. The second
dose, taken approximately 5 hours before the procedure, minimizes the
buildup of thick intestinal secretions in the colon, resulting in
improved polyp detection.6,12,14
Low-volume 2-L PEG preparations such as HalfLytely (which includes
bisacodyl) and MoviPrep (which contains ascorbic acid) are also
alternatives to full-volume regimens. The additional ingredients act
synergistically, with PEG causing a reduction in volume without
compromising safety and efficacy.10 With HalfLytely, after
the bisacodyl tablets are taken, the patient should wait for a bowel
movement to occur, or at least 6 hours, before consuming the PEG
solution.15 MoviPrep may be given as either a one-dose
regimen the evening before colonoscopy or a split-dose regimen of 1 L
followed by 0.5 L of clear liquid the evening before, then repeated the
Most PEG-based solutions contain electrolytes, thereby preventing
shifts in fluid and electrolytes. Some providers recommend
MiraLAX—PEG-3350 containing no electrolytes—as a more tolerable
alternative to the full-volume regimens. Although widely used in
practice, MiraLAX as a bowel preparation is an off-label use. As a bowel
preparation, MiraLAX should be mixed with 2 L of clear liquid or a
sports drink and consumed as 8 oz every 10 minutes the evening before
the procedure.17 In theory, the lack of electrolyte
supplementation increases the risk of electrolyte imbalances.
Nevertheless, MiraLAX has been administered as one-dose and split-dose
regimens. The split-dose regimen was found to be less efficacious for
bowel cleansing compared with split-dose PEG.18,19
Overall, the efficacy and tolerability of PEG-based preparations are
generally considered inferior to those of NaP preparations. Conversely,
compared with NaP, PEG-based products are thought to be a safer
alternative for patients at risk for developing complications secondary
to fluid and electrolyte imbalances (e.g., patients with renal failure,
liver failure, or congestive heart failure [CHF]). In addition,
PEG-based solutions do not appear to alter the cells of the colonic
mucosa, making it an effective option for patients with suspected
inflammatory bowel disease.20
NaP Preparation: NaP was originally developed to avoid the large-volume ingestion associated with PEG preparations.17
NaP works as a hyperosmotic laxative, drawing water into the lumen of
the colon to stimulate peristalsis and catharsis. Until 2008, when the
FDA issued a black box warning, Fleet Phospho-soda was a commonly used
OTC NaP preparation for bowel cleansing. Because of the increased risk
of acute phosphate nephropathy (APN), which may result in permanent
renal impairment, this solution is no longer available on the U.S.
market, according to the manufacturer (oral communication, August 2013).8,21 Currently,
only tablet formulations of NaP (Visicol, OsmoPrep) are available in
the U.S. The main difference between Visicol and OsmoPrep is the
presence or absence of microcrystalline cellulose (MCC).8,22,23
This insoluble, inactive compound is thought to produce a residue that
theoretically may reduce visualization of the colonic mucosa during
colonoscopy.24 Visicol contains MCC and requires the
ingestion of 40 tablets to complete the regimen; OsmoPrep, which is
MCC-free, requires 32 tablets (TABLE 1).
A common misconception about NaP products is that hydration is not
necessary. As with the solution, the tablets induce cathartic effects
and must be taken with 4 L of clear liquid to maintain adequate
hydration and prevent serious adverse effects (AEs), such as fluid and
electrolyte imbalances.22,23,25 Additionally, these tablet formulations carry the risk of APN and should be monitored accordingly.
In general, NaP products are considered more effective and tolerable
than full-volume PEG products, but they may be less safe, particularly
in patients with kidney disease, CHF, advanced liver disease, or a
Magnesium Citrate: Although not FDA-approved as a
bowel preparation, magnesium citrate is a hyperosmotic laxative that
has long been a component of bowel-cleansing regimens. In addition to
drawing fluid into the colon and increasing motility, magnesium citrate
also stimulates the release of cholecystokinin, leading to intestinal
accumulation of fluid and electrolytes and eventual evacuation of the
Magnesium citrate typically is not used as monotherapy for bowel
cleansing. It is frequently administered with bisacodyl and has been
used as an adjunct to low-volume PEG for colonoscopy preparation.
Patients with abdominal pain or hemorrhage or renal dysfunction should
avoid its use. Although they are considered less tolerable than NaP
products, regimens containing magnesium citrate are generally well
tolerated. For this reason, along with its relative affordability,
magnesium citrate may be considered an alternative for appropriate
Newer Bowel Preparations
Over the last several years, three new products have been
FDA-approved for use in colonoscopy preparation. These agents were
developed to better address the challenge of improving tolerability
while maintaining efficacy. Caution should be exercised in patients with
a history of arrhythmias, seizures, renal impairment, significant
gastrointestinal (GI) disease, impaired gag reflex, regurgitation or
aspiration, and fluid or electrolyte imbalances.27-29
Oral Sulfate Solution (SUPREP): SUPREP is a low-volume
osmotic laxative containing a combination of poorly absorbed sulfate
salts (sodium sulfate, potassium sulfate, magnesium sulfate). These
salts draw water into the lumen of the GI tract to promote cathartic
To decrease GI AEs, including vomiting, the manufacturer recommends
administering SUPREP as a split-dose regimen. On the evening before the
procedure, the first 16-oz bottle should be consumed, followed by 32 oz
of water, over 1 hour. On the morning of the procedure, at least 2 hours
prior to the procedure, the regimen is repeated with the second 16-oz
Clinical trials evaluating both one-dose and split-dose regimens have
demonstrated similar efficacy and safety compared with PEG
preparations. SUPREP, therefore, may be an alternative, particularly in
patients unable to tolerate PEG.30
Sodium Picosulfate Preparation (Prepopik): Prepopik
(sodium picosulfate, magnesium hydroxide, anhydrous citric acid) is a
10-oz preparation that combines a stimulant laxative with an osmotic
laxative, making it the lowest-volume preparation currently available in
the U.S. Sodium picosulfate is a prodrug that is hydrolyzed and
activated by colonic bacteria to produce peristalsis. Magnesium
hydroxide and anhydrous citric acid react with water to form magnesium
citrate, further promoting a laxative effect.8,28
Prepopik is contraindicated in patients with severely reduced renal
function. Prior or current use of antibiotics may decrease the
preparation’s efficacy because of the conversion of sodium picosulfate
to its active metabolite by colonic bacteria, so evaluation is necessary
in this case.28
When one-dose regimens of low-volume PEG-3350 plus bisacodyl tablets
were compared with Prepopik, both preparations were equally effective
for bowel cleansing. In a comparison of split-dose regimens, Prepopik
had slightly superior efficacy. Tolerability was also improved with
Prepopik. Bowel preparations containing this combination have
been studied and used extensively outside the U.S. and have achieved
similar results, further supporting this preparation’s role as an
Combination Osmotic Laxative (Suclear): Suclear (sodium
sulfate, potassium sulfate, and magnesium sulfate; PEG-3350, sodium
chloride, sodium bicarbonate, potassium chloride), the latest bowel
preparation approved by the FDA (January 2013), combines the osmotic
effects of oral sulfates and PEG to induce cathartic effects in the GI
Split-dose administration of Suclear is preferred. On the evening
before the procedure, the 6-oz bottle of oral sulfate solution should be
diluted and consumed, followed by 32 oz of water, over 2 hours. On the
morning of the procedure, the 2-L jug of PEG should be reconstituted and
consumed at a rate of 16 oz every 20 minutes, to be completed 2 hours
In two different studies comparing one-dose regimens and split-dose
regimens of low-volume PEG-3350, with or without bisacodyl tablets, the
proportion of successful colon cleansing was similar between groups.
Suclear may be considered an alternative bowel preparation.29
Before the widespread use of PEG, the enema was an important
component of bowel preparation. The increased discomfort and lack of
improvement in the quality of bowel cleansing have minimized the
popularity of this agent. The enema appears to maintain its role as an
adjunct in patients who present for colonoscopy with inadequate bowel
The need to ingest a large volume of fluid has been one of the
greatest challenges in successful administration of bowel preparations.
Laxatives such as senna, bisacodyl, and magnesium citrate have been used
for their additive cathartic effects, reducing the volume of PEG
required for cleansing.
GI symptoms such as nausea, bloating, and gas also limit the
tolerability of bowel preparations. These symptoms can be alleviated
with use of adjunct agents. Metoclopramide has been shown to reduce the
occurrence of nausea and bloating. Simethicone can reduce bloating and
gas, and it also may be used to eliminate foam formation and improve
visualization for colonoscopy screenings.14,24,26
Education and Counseling
Patient education regarding preparation, administration, and AE
management reduces the rates of missed polyps (up to 48%), procedure
complications, and repeat colonoscopies.10,32,33 Community
pharmacists can play a key role in ensuring that patients are prepared
for colonoscopy. Information on topics such as timing, concomitant
medications, diet, improving tolerability, and hydration is helpful for
successful bowel preparation.
For optimal colonic cleansing, at least a portion of the bowel
preparation must be ingested within 6 to 8 hours of the procedure. To
ensure optimal visualization of the colon, patients must precisely
follow the instructions provided by their healthcare professional (HCP)
or the manufacturer.34
Patients should review their current medication list with their HCP.
For patients taking antithrombotic agents, the risks and benefits of
interrupting therapy should be weighed. OTC medications with bleeding
risk (e.g., aspirin, other nonsteroidal anti-inflammatory drugs) are
generally safe to continue, but should be reviewed with the HCP.
Patients taking diabetic medications, particularly insulin, may need to
adjust the dose when completing a bowel-preparation regimen. All other
prescription medications generally can be continued, unless otherwise
advised. Patients taking diuretics, ACE inhibitors, or angiotensin
receptor blockers should use NaP-containing regimens with caution. OTC
bulk-forming laxatives (e.g., Metamucil, Citrucel), as well as iron and
iron-containing products (e.g., multivitamins), should be avoided 5 days
before the procedure.26
In general, for 2 to 3 days prior to a colonoscopy (range 1-5 days,
depending upon HCP instructions), patients are advised to adhere to a
low-residue diet, limiting intake of fiber and other indigestible foods.
Patients should also maintain a clear liquid diet starting 24 hours
before the procedure. Red or purple liquids, alcohol, and milk or
milk-based fluids should be avoided. In general, nothing should be
ingested 2 hours prior to the procedure.26,34,35
Suggestions addressing taste and volume have been developed to
improve the tolerability of bowel preparations. Pharmacists can work
with HCPs to suggest split-dose regimens, lower-volume preparations, and
the use of adjunctive agents to address concerns regarding fluid
volume. To improve taste, patients can chill the solutions, use a straw
to bypass the taste buds, or add flavor (e.g., the included flavor
packets, clear sugar-free powder mixes, or lemon juice). Sucking on
fresh lemon or lime slices or rubbing them on the tongue may also
improve palatability, as citrus appears to best mask the saltiness of
Because of the significant fluid and electrolyte imbalance that can
result from bowel-cleansing regimens, adequate hydration throughout the
preparation period is essential. Patients should be advised to consume
at least 64 oz (approximately 2 L) of clear liquid on the day before the
colonoscopy. Clear fluids may be consumed for up to 2 hours prior to
the procedure. A minimum of 32 oz of fluid should be consumed within 8
hours after the colonoscopy to prevent any complications.25
Patients also should be counseled about common AEs (e.g., diarrhea,
nausea, bloating) and the need to stay at home or near a restroom
because of the frequent bowel movements triggered by the preparation.
After ingestion, the expected onset of action is approximately 1 hour
for PEG-based bowel preparations and 3 to 6 hours for NaP preparations.8 Patients may experience anal irritation, which can be alleviated by using wet wipes or petrolatum.26
Over the past three decades, the number of adults screened for CRC in the U.S. has increased significantly.2 The
diagnostic accuracy of colonoscopy is limited by inadequate bowel
cleansing, often because of poor patient compliance and tolerability.
Despite the development of newer bowel preparations, there continues to
be no ideal regimen. Adjunctive strategies may be used to improve
screening visualization, palatability, and GI AEs. Community pharmacists
can be a valuable resource in ensuring a successful colonoscopy.
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