The effect of stimulant laxatives and polyethylene glycol-electrolyte lavage solution for colonoscopy preparation on serum electrolytes and hemodynamics.

We have previously shown that magnesium citrate or bisacodyl before polyethylene glycol electrolyte lavage solution (PEG-ELS) improves colonoscopy preparation. Patients prefer this to preparation with full-volume PEG-ELS alone. However, such combinations might cause undesirable changes in hemodynamics or serum electrolytes. This study examined the effects of these combinations on heart rate, blood pressure, and serum electrolytes. We randomized 68 consecutive patients undergoing colonoscopy to one of three preparations. Group 1 received 4 L of PEG-ELS, group 2 received 2 L of PEG-ELS with 20 mg bisacodyl, and group 3 received 2 L of PEG-ELS preceded by 296 mL of magnesium citrate. Heart rate, blood pressure, and serum electrolytes were measured before starting the preparation and immediately before colonoscopy. Mean serum magnesium fell by 0.01 mg/dL and 0.11 mg/dL in groups 1 and 2, respectively, and rose by 0.06 mg/dL in group 3 (p = 0.044). There were no other significant changes. Statistically significant changes in serum magnesium after preparation with PEG-ELS and a stimulant laxative are minor and probably of no clinical relevance. Two liters of PEG-ELS with a stimulant laxative is safe and effective for colonoscopy.