Monday Pharmaceutical Mystery: March 16


How can this patient better tolerate polyethylene glycol (PEG)-electrolyte lavage solution?

A middle-aged man comes into the pharmacy with a half-filled jug of polyethylene glycol (PEG)-electrolyte lavage solution. He asks to speak with the pharmacist. You approach the counter, and he says he is trying to prepare for a routine colonoscopy, but he is unable to drink the entire bottle of PEG's in order to prepare for the test tomorrow. He can only consume about half of the bottle, and then he starts vomiting if he tries to drink any more. He asks you for some helpful recommendations.

The man says that this is the third attempt to drink the bowel prep. He had to cancel his prior 2 tests because of the nausea and vomiting. He says it is a routine screening, and he does not have any bowel disease to his knowledge. The medications he takes are on file:

  • cetiriizne 10mg qd for allergies,
  • pantoprazol 40mg qd for GERD
  • pravastatin 40mg qhs for cholesterol
  • gabapentin 300mg tid for arthritis

Mystery: Is there anything this gentleman can do so he does not have to cancel his test for the third time?

Solution: Yes, there are several options involving mag-citrate, bisacodyl (Dulcolax), polyethylene glycol 3350 (Miralax) mixed with a clear electrolyte replacement beverage (Gatorade), and variations of large volume PEG's. Fortunately, this patient has no comorbidity that could limit his options. However, since he has already consumed half of the jug, the easiest regimen is to go with the split dose method. Split-dose refers to administration of half of the colon cleansing agent the evening prior to the colonoscopy, and the second half the morning of the colonoscopy.

It is recommended that patients consume their morning dose 5 hours prior to the procedure. For patients with early morning procedures, this may require that the patient take the morning dose as early as 2 a.m. This is consistent with American Society for Anesthesiology guidelines that state prior to a sedated procedure, patients should fast for a minimum of 2 hours following clear liquid ingestion or 6 hours for a light meal.1

In meta-analyses of randomized trials of split-dose preparation versus single dose evening before dosing, patients who received a split-dose preparation were more likely to have an adequate preparation, and they were less likely to discontinue the preparation due to less nausea and vomiting.2,3


  • American Society of Anesthesiologists Task Force on Sedation and Analgesia by Non-Anesthesiologists. Practice guidelines for sedation and analgesia by non-anesthesiologists. Anesthesiology 2002; 96:1004.
  • Bucci C, Rotondano G, Hassan C, et al. Optimal bowel cleansing for colonoscopy: split the dose! A series of meta-analyses of controlled studies. Gastrointest Endosc 2014; 80:566
  • Kilgore TW, Abdinoor AA, Szary NM, et al. Bowel preparation with split-dose polyethylene glycol before colonoscopy: a meta-analysis of randomized controlled trials. Gastrointest Endosc 2011; 73:124

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