PEG-Sports Drink Bowel Prep: Physiology of Electrolyte Imbalance: Presidential Poster

Abstract

Introduction: The ideal colonoscopy preparation (prep) should be proven safe and effective. Substantial review of prep marketing applications by Health Authorities assures an evidence basis that is not available for unapproved preps such as PEG-Sports Drink (PEG-SD). As SDs were designed to replace electrolytes lost from perspiration, not from diarrhea, it is not surprising that PEG-SD has been associated with severe electrolyte deficiencies, seizures, death and diminished efficacy. Therefore, we examined some of the fundamental pharmacodynamic aspects of PEG-SD as compared to an FDA-approved prep, OSS (SUPREP). Methods: Healthy men (< 50 yoa) were restricted to clinic on ad-libitum liquid diet. Some received 10 mg of bisacodyl in the afternoon, 119 g of PEG-3350 in 0.95L of SD in the evening and a second dose of PEG-SD in the morning. Others received OSS as split dose prep without bisacodyl. Blood, urine and feces were collected for balance studies; surrogate markers were total stool volume and final bowel movement (BM) % solids Results: The Table shows that PEG-SD produced statistically significant higher stool solids, smaller stool volumes and greater shifts in fluid and electrolyte balance compared to OSS. PEG-SD subjects had statistically significant losses of Na, K and Mg compared to OSS. After OSS, cations did not significantly change from zero. Remarkably, both gastric absorption and urinary excretion of water were 2L greater after PEG-SD. Stool osmolarity was more than 2X higher after PEG-SD, The first BM after OSS was significantly sooner (40 min) versus 83 min with PEG-SD. Conclusion: Unlike balanced OSS, PEG-SD significantly disturbs water and electrolyte physiology and produces low volume, poorly cleansed stool. The wide variability of stool volume and solids suggest that PEG-SD will have sub-optimal bowel cleansing. Together these may underlie the electrolyte abnormalities and lower efficacy seen with PEG-SD. The inadequate levels of electrolytes in PEG-SD favor hypervolemia and hyponatremia. Such changes in young healthy volunteers may be worsened in older patients undergoing colonoscopy with certain co-morbidities and concomitant medications. The sugars in PEG-SD may slow gastric emptying and delay the first BM. Also, they appear to reach the colon, increase stool osmolality above the reference range and may increase combustible gas. Evidence-based physiological safety measures should discourage the use of un-approved bowel preps when safer, more effective alternatives exist.Table 1: Stool and Balance after PEG-SD or OSS