Management of Sulfonylureas for Colonoscopy
Yes, sulfonylureas must be held on the day of colonoscopy and the night before if fasting is required for bowel preparation, due to significant hypoglycemia risk when patients are NPO.
Rationale for Holding Sulfonylureas
Sulfonylureas stimulate insulin secretion independent of glucose levels, creating substantial hypoglycemia risk when patients cannot eat during bowel preparation and the fasting period before colonoscopy 1.
The fasting period for colonoscopy extends beyond the typical overnight fast because patients begin clear liquids the day before the procedure and complete bowel preparation at least 2 hours before the scheduled time 2, 3.
Older adults and patients with impaired renal function face amplified hypoglycemia risk because sulfonylureas and their active metabolites accumulate with reduced kidney function, and aging impairs counter-regulatory responses to low blood glucose 1.
Specific Timing Protocol
Hold sulfonylureas starting the evening before colonoscopy when the patient transitions to clear liquids only (typically after the first bowel preparation dose around 6-8 PM the night before) 3, 4.
Do not administer the morning dose on the day of the procedure, as patients will be NPO except for clear liquids until 2 hours before colonoscopy 2, 4.
For split-dose bowel preparation regimens (the strongly recommended approach), the second preparation dose is taken 4-6 hours before the procedure and completed at least 2 hours prior, meaning patients have minimal to no caloric intake during this entire window 2, 3.
Contrast with Other Diabetes Medications
GLP-1 receptor agonists require a 7-day discontinuation before colonoscopy due to delayed gastric emptying that compromises bowel preparation quality and increases aspiration risk 1.
DPP-4 inhibitors do not require discontinuation because they are glucose-dependent and carry minimal hypoglycemia risk during fasting 1.
Metformin can typically be continued through colonoscopy preparation in patients with normal renal function, as it does not cause hypoglycemia when used as monotherapy 1.
Glucose Monitoring During Discontinuation
Check blood glucose levels more frequently (at minimum before each meal and at bedtime) during the period when sulfonylureas are held, as glycemic control will be affected 1.
Patients should have access to glucose tablets or another rapid-acting carbohydrate source in case hypoglycemia occurs despite holding the medication, particularly if they have been on long-acting sulfonylureas 1.
Post-Procedure Resumption
Resume sulfonylureas after the colonoscopy once normal eating has been established and the patient can tolerate a full meal 1.
Ensure adequate hydration before restarting the medication, as dehydration from bowel preparation can affect drug clearance and increase hypoglycemia risk 1.
Common Pitfalls to Avoid
Do not instruct patients to take "half doses" of sulfonylureas during preparation—the hypoglycemia risk remains substantial even with reduced doses when patients are fasting 1.
Do not assume that short-acting sulfonylureas are safe to continue—all sulfonylureas carry hypoglycemia risk during prolonged fasting, though long-acting agents (glyburide, glimepiride) pose the highest risk 1.
Failing to provide clear written instructions about medication holds is a major cause of adverse events; both verbal and written education must explicitly state which diabetes medications to hold and when 2, 3.