Glyburide
glibenclamide — DiaBeta, Glynase PresTab
Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Type 2 diabetes mellitus — adjunct to diet and exercise | Adults | Monotherapy or combination with other oral agents / insulin | FDA Approved |
Glyburide is approved exclusively for type 2 diabetes management as an adjunct to lifestyle modification. It works by stimulating endogenous insulin secretion from functioning pancreatic beta cells and is therefore ineffective in type 1 diabetes or diabetic ketoacidosis. Current ADA guidelines (2023) position sulfonylureas as viable second-line options when metformin is insufficient or contraindicated, though they note that agents other than glyburide may be preferred within the sulfonylurea class due to hypoglycemia risk considerations.
Gestational diabetes mellitus: Glyburide has been studied as an alternative to insulin for glycemic management during pregnancy. While some institutions use it selectively, most major guidelines recommend insulin as first-line pharmacotherapy in pregnancy. Evidence quality: Moderate (multiple RCTs, but concerns regarding neonatal hypoglycemia and macrosomia persist).
Neonatal diabetes (specific KCNJ11/ABCC8 mutations): Investigational use in neonates with activating potassium channel mutations responsive to sulfonylurea therapy. Evidence quality: Low (case series and small studies).
Dosing
Regular (Non-Micronized) Tablets — DiaBeta
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| T2DM — treatment-naive, initial monotherapy | 2.5–5 mg once daily | 1.25–20 mg/day | 20 mg/day | Give with breakfast; increase by ≤2.5 mg/day at weekly intervals Doses >10 mg/day may be split BID |
| T2DM — hypoglycemia-prone patients (elderly, debilitated, malnourished) | 1.25 mg once daily | 1.25–10 mg/day | 20 mg/day | Conservative titration; avoid maximum doses in frail patients ADA recommends avoiding glyburide in elderly (2023) |
| T2DM — switching from another oral sulfonylurea | 2.5–5 mg once daily | Titrate per response | 20 mg/day | No transition period needed (except from chlorpropamide) If switching from chlorpropamide, observe closely for 2 weeks due to overlapping effects |
| T2DM — transitioning from insulin (<20 units/day) | 2.5–5 mg once daily | Titrate per response | 20 mg/day | Discontinue insulin; start glyburide directly FDA PI |
| T2DM — transitioning from insulin (20–40 units/day) | 5 mg once daily | Titrate per response | 20 mg/day | Discontinue insulin; begin glyburide as sole agent FDA PI |
| T2DM — transitioning from insulin (>40 units/day) | 5 mg once daily | Titrate per response | 20 mg/day | Reduce insulin by 50%; start glyburide concurrently; taper insulin gradually as glyburide dose increases Increase glyburide by 1.25–2.5 mg/day |
| T2DM — renal impairment (CrCl ≥30 mL/min) | 1.25 mg once daily | Conservative titration | Use lower end of range | Elevated drug levels increase hypoglycemia risk; active metabolites accumulate Consider alternatives if CrCl <30 mL/min |
Micronized Tablets — Glynase PresTab
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| T2DM — initial monotherapy | 1.5–3 mg once daily | 0.75–12 mg/day | 12 mg/day | Not bioequivalent to regular tablets; do not substitute mg-for-mg Titrate by ≤1.5 mg/day at weekly intervals |
| T2DM — hypoglycemia-prone patients | 0.75 mg once daily | Conservative titration | 12 mg/day | Extra caution in elderly, debilitated, or hepatically impaired patients |
Micronized glyburide tablets (Glynase) are NOT bioequivalent to regular tablets (DiaBeta). The micronized formulation has improved particle size and bioavailability, meaning lower milligram doses achieve comparable blood levels. Patients must be retitrated if switching between formulations. A rough conversion is micronized 3 mg ≈ regular 5 mg, but individualized dose adjustment based on blood glucose response is essential.
Pharmacology
Mechanism of Action
Glyburide exerts its glucose-lowering effect primarily by binding to the sulfonylurea receptor 1 (SUR1) subunit of ATP-sensitive potassium (KATP) channels on pancreatic beta cells. This binding closes the channel, which depolarizes the cell membrane and triggers voltage-gated calcium channel opening. The subsequent influx of calcium ions stimulates insulin granule exocytosis. Glyburide has uniquely high affinity for SUR1 and dissociates slowly from the receptor, which contributes to its prolonged duration of action and higher hypoglycemia risk relative to other sulfonylureas. Beyond direct insulinotropic effects, chronic glyburide therapy also enhances peripheral insulin sensitivity and reduces basal hepatic glucose output, though the relative contribution of these extrapancreatic actions is debated.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Significant absorption within 1 h; Tmax ~4 h (regular), ~2–3 h (micronized); BCS Class II (low solubility, high permeability) | Variable bioavailability between formulations; take with breakfast to improve consistency and reduce fasting hypoglycemia risk |
| Distribution | Vd ~0.155 L/kg; >99% protein bound (albumin, non-ionic binding) | Non-ionic protein binding means lower displacement risk from acidic drugs compared to first-generation sulfonylureas; crosses placenta |
| Metabolism | Hepatic via CYP2C9 (major) and CYP3A4; two metabolites: 4-trans-hydroxy (1/400th potency) and 3-cis-hydroxy (1/40th potency) | CYP2C9 inhibitors can raise glyburide levels; metabolites are weakly active but may contribute in renal impairment |
| Elimination | Terminal t½ ~10 h (parent + metabolites); excreted as metabolites: ~50% renal, ~50% biliary | Dual excretory pathway is unique among sulfonylureas; prolonged effect persists ~24 h, allowing once-daily dosing; renal or hepatic impairment can extend action |
Side Effects
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Hypoglycemia (all severity) | 20–40% | Most common adverse effect; meta-analysis (Gangji et al., 2007) showed 52% higher risk vs other secretagogues overall and 83% higher risk vs other sulfonylureas specifically; dose-dependent and worsened by missed meals, excessive exercise, or renal impairment |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Nausea | 1–3% | Dose-related; may improve with dose reduction or taking consistently with food |
| Epigastric fullness / heartburn | 1–2% | GI effects collectively affect ~1–2% of patients; typically self-limiting |
| Diarrhea | 1–2% | Consider dose reduction if persistent |
| Weight gain | ~2–5% | Average gain ~2–3 kg (approximately 5 lbs over several months); insulin-mediated lipogenesis; less pronounced than with some other secretagogues per ADA review |
| Dizziness / headache | 1–3% | Often related to blood glucose fluctuations rather than a direct drug effect |
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Severe hypoglycemia (loss of consciousness, seizure, requiring assistance) | ~1–5% | Any time; higher risk during first weeks and with dose changes | Administer IV dextrose or IM glucagon; hospitalize and monitor for 24–72 h due to prolonged drug action; dose reduction or discontinuation |
| Cholestatic jaundice / hepatitis | Rare (<0.1%) | Weeks to months after initiation | Discontinue immediately; monitor LFTs; hepatitis may progress to liver failure if not recognized |
| Hemolytic anemia (especially with G6PD deficiency) | Rare | Variable; may occur at any time | Discontinue glyburide; treat anemia; use a non-sulfonylurea alternative; screen for G6PD deficiency before initiation in at-risk populations |
| Hyponatremia / SIADH | Very rare | Weeks to months | Check serum sodium; discontinue if confirmed; fluid restriction as needed |
| Blood dyscrasias (agranulocytosis, thrombocytopenia, aplastic anemia) | Very rare | Weeks to months | Obtain CBC; discontinue glyburide; refer to hematology if indicated |
| Severe allergic reaction (angioedema, vasculitis) | Very rare | Days to weeks after initiation | Discontinue permanently; treat reaction; cross-sensitivity with other sulfonylureas possible |
| Reason for Discontinuation | Incidence | Context |
|---|---|---|
| Recurrent hypoglycemia | <1% | More common in elderly and renally impaired patients |
| GI adverse effects | <2% | Nausea, vomiting, or diarrhea severe enough to warrant stopping |
| Hepatotoxicity | Rare | Idiosyncratic; requires immediate discontinuation when detected |
Because glyburide has a prolonged duration of action (~24 hours), hypoglycemic episodes can be sustained and severe, lasting 4–10 days in some neonatal or elderly cases. Mild episodes should be treated with 15–20 g of fast-acting carbohydrate (glucose tablets, juice) and rechecked in 15 minutes. Severe episodes (altered consciousness, seizure) require IV dextrose and prolonged monitoring — a single correction may not be sufficient. Always consider whether the patient is appropriate for a shorter-acting sulfonylurea (e.g., glipizide, glimepiride) or an alternative drug class entirely.
Drug Interactions
Glyburide is metabolized primarily by CYP2C9 and to a lesser extent by CYP3A4. It is also a substrate of organic anion transporting polypeptide 1B1 (OATP1B1) and breast cancer resistance protein (BCRP). Its >99% protein binding is predominantly non-ionic, which reduces but does not eliminate the risk of protein displacement interactions. Key clinically significant interactions are detailed below.
Several drug classes can antagonize glyburide’s glucose-lowering effect by causing hyperglycemia. These include thiazide diuretics, corticosteroids, thyroid hormones, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blockers, isoniazid, and phenothiazines. When starting or stopping any of these agents in a patient on glyburide, blood glucose should be monitored more closely and the glyburide dose adjusted as needed (FDA PI).
Monitoring
-
Blood Glucose (Fasting & Pre-Prandial)
Baseline, then regularly during titration
Routine Self-monitoring of blood glucose is essential during dose titration and whenever clinical circumstances change (new illness, altered diet, new interacting drug). Target fasting glucose per individualized HbA1c goals. -
HbA1c
Baseline, then every 3–6 months
Routine Assess glycemic control and need for therapy intensification or de-intensification. Individualize targets (typically <7% per ADA; more relaxed in elderly/frail patients). -
Renal Function (Creatinine, eGFR)
Baseline, then at least annually
Routine Declining renal function elevates glyburide and metabolite levels, increasing hypoglycemia risk. Consider switching to a shorter-acting sulfonylurea or alternative class if eGFR falls significantly. -
Hepatic Function (LFTs)
Baseline; repeat if symptoms arise
Trigger-Based Cholestatic hepatitis is an idiosyncratic reaction. Obtain LFTs if the patient develops jaundice, dark urine, right upper quadrant pain, or unexplained fatigue. Discontinue if confirmed. -
Complete Blood Count
As clinically indicated
Trigger-Based Blood dyscrasias (agranulocytosis, thrombocytopenia, hemolytic anemia) are rare but serious. Obtain CBC if unexplained fever, sore throat, bruising, or pallor occurs. -
Serum Sodium
If symptoms of hyponatremia develop
Trigger-Based SIADH is a very rare complication. Check sodium if the patient presents with confusion, nausea, headache, or seizures that cannot be attributed to hypoglycemia alone. -
Body Weight
Every visit
Routine Weight gain is expected with sulfonylurea therapy. Persistent weight gain should prompt reassessment of the treatment plan and consideration of weight-neutral or weight-loss agents.
Contraindications & Cautions
Absolute Contraindications
- Type 1 diabetes mellitus — glyburide requires functioning beta cells and is ineffective in insulin-dependent disease
- Diabetic ketoacidosis (DKA) — requires insulin therapy, not oral sulfonylureas
- Known hypersensitivity to glyburide or any component of the formulation
- Concomitant bosentan use — contraindicated due to hepatotoxicity risk and mutual interference (FDA PI)
Relative Contraindications (Specialist Input Recommended)
- Severe renal impairment (eGFR <30 mL/min) — marked accumulation of active metabolites; use alternative agents with safer renal profiles
- Severe hepatic disease — impaired metabolism prolongs drug action and diminishes gluconeogenic reserve, compounding hypoglycemia risk
- G6PD deficiency — risk of hemolytic anemia; a non-sulfonylurea alternative should be considered; if glyburide must be used, baseline G6PD testing and close hematologic monitoring are needed
- Elderly patients (≥65 years) — ADA 2023 guidelines recommend avoiding glyburide in older adults due to the high risk of prolonged severe hypoglycemia; shorter-acting sulfonylureas or other classes preferred
Use with Caution
- Moderate renal impairment (eGFR 30–60 mL/min) — conservative dosing and more frequent glucose monitoring
- Debilitated, malnourished, or alcohol-misusing patients — depleted glycogen stores heighten hypoglycemia severity
- Adrenal or pituitary insufficiency — impaired counter-regulatory hormones increase hypoglycemia susceptibility
- Patients taking beta-blockers — may mask sympathetic hypoglycemia warning signs
- Acute illness, surgery, or trauma — temporary transition to insulin may be necessary; restart glyburide when stable
The University Group Diabetes Program (UGDP) reported that patients treated with tolbutamide (a first-generation sulfonylurea) for 5–8 years had a cardiovascular mortality rate approximately 2.5 times higher than patients treated with diet alone. While this study involved tolbutamide specifically, the FDA considers that this warning may apply to glyburide and other members of the sulfonylurea class given their similar mechanisms. Patients should be informed of the potential risks and benefits of glyburide therapy and of alternative treatment options. More recent observational data (Gangji et al., 2007 meta-analysis) did not find an increased risk of cardiovascular events or death with glyburide compared to other secretagogues.
Patient Counselling
Purpose of Therapy
Glyburide helps control blood sugar levels in type 2 diabetes by stimulating the pancreas to release more of the body’s own insulin. It works best when combined with a consistent meal plan and regular physical activity. It does not cure diabetes but helps prevent long-term complications such as kidney damage, vision loss, and nerve problems when blood sugar is well controlled.
How to Take
Take glyburide with breakfast or the first main meal of the day. If your doctor prescribes a twice-daily dose, take the second dose with the evening meal. Swallow tablets whole. Never skip meals after taking glyburide, as this significantly increases the risk of low blood sugar. If you are also taking colesevelam (a cholesterol medication), take glyburide at least 4 hours before it.
Sources
- Glyburide (DiaBeta) Tablets USP — FDA-Approved Prescribing Information. Sanofi-Aventis. Revised 2017. FDA Label (PDF) Primary regulatory source for dosing, pharmacokinetics, contraindications, and adverse reactions for regular (non-micronized) glyburide tablets.
- Glyburide Micronized Tablets (Glynase PresTab) — FDA-Approved Prescribing Information. Pfizer. Revised 2011. FDA Label (PDF) Prescribing information for the micronized formulation; documents bioavailability differences from regular tablets and adjusted dosing.
- Glyburide and Metformin Hydrochloride (Glucovance) Tablets — FDA-Approved Prescribing Information. Revised 2018. FDA Label (PDF) Combination product label providing additional pharmacokinetic and clinical trial data for glyburide.
- UK Prospective Diabetes Study (UKPDS) Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet. 1998;352(9131):837–853. DOI Landmark trial demonstrating microvascular benefit of intensive glucose control with sulfonylureas including glyburide in newly diagnosed type 2 diabetes.
- Gangji AS, Cukierman T, Gerstein HC, Goldsmith CH, Clase CM. A systematic review and meta-analysis of hypoglycemia and cardiovascular events: a comparison of glyburide with other secretagogues and with insulin. Diabetes Care. 2007;30(2):389–394. DOI Meta-analysis showing 52–83% higher hypoglycemia risk with glyburide compared to other sulfonylureas and secretagogues; no increased cardiovascular event risk.
- Langer O, Conway DL, Berkus MD, Xenakis EM, Gonzales O. A comparison of glyburide and insulin in women with gestational diabetes mellitus. N Engl J Med. 2000;343(16):1134–1138. DOI Key RCT evaluating glyburide versus insulin in gestational diabetes; established initial evidence for off-label use in pregnancy.
- ElSayed NA, Aleppo G, Aroda VR, et al. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes — 2023. Diabetes Care. 2023;46(Suppl 1):S140–S157. DOI ADA 2023 Standards of Care positioning sulfonylureas as second-line therapy; recommends avoiding glyburide in elderly due to hypoglycemia risk.
- Garber AJ, Handelsman Y, Grunberger G, et al. Consensus Statement by the American Association of Clinical Endocrinologists and American College of Endocrinology on the Comprehensive Type 2 Diabetes Management Algorithm — 2019 Executive Summary. Endocr Pract. 2019;25(1):69–100. DOI AACE/ACE consensus noting that if a sulfonylurea is chosen, agents other than glyburide are generally preferred.
- Feldman JM. Glyburide: a second-generation sulfonylurea hypoglycemic agent. History, chemistry, metabolism, pharmacokinetics, clinical use and adverse effects. Pharmacotherapy. 1985;5(2):43–62. DOI Comprehensive early review of glyburide pharmacology, metabolism via CYP2C9/3A4, and adverse effect profile.
- Ashcroft FM, Gribble FM. ATP-sensitive K+ channels and insulin secretion: their role in health and disease. Diabetologia. 1999;42(8):903–919. DOI Foundational review of K-ATP channel physiology explaining the molecular target of sulfonylureas including glyburide.
- Antal EJ, Harkness JE, Batts DH, Stevenson JG, Albert KS, Welling PG. Pharmacokinetics of glyburide. Am J Med. 1985;79(3B):44–52. DOI Defines the two-compartment PK model, 99% albumin binding, and dual biliary-renal excretion pathway.
- Pearson JG, Antal EJ, Raehl CL, et al. Pharmacokinetic disposition of 14C-glyburide in patients with varying renal function. Clin Pharmacol Ther. 1986;39(3):318–324. DOI Demonstrates that glyburide half-life is not significantly altered until CrCl falls below ~30 mL/min; informs renal dose adjustment thresholds.
- Hardin MD, Jacobs TF. Glyburide. In: StatPearls. Treasure Island, FL: StatPearls Publishing; 2023. NCBI Bookshelf Concise clinical review covering indications, mechanism, adverse effects, and monitoring with current ADA guideline integration.