Sulfonylureas

Why this poison is interesting

Sulfonylureas are metformin's mirror image. They share a clinic and a diagnosis and almost nothing else in overdose: where metformin causes a lactic acidosis and not hypoglycaemia, a sulfonylurea causes profound hypoglycaemia and not acidosis. And the hypoglycaemia is the difficult kind — delayed, recurrent and resistant to glucose alone — because the drug is not supplying insulin, it is making the patient supply their own.¹³

• The poison is endogenous insulin. Sulfonylureas close the ATP-sensitive potassium channel on the pancreatic beta cell, the final common step the body itself uses to release insulin. The result is sustained, glucose-independent insulin secretion — the patient's own hormone, turned on and left on.¹³ Established
• Glucose alone is a trap. Giving dextrose raises the blood sugar, which is exactly the stimulus a primed beta cell responds to, so a bolus can provoke a further surge of insulin and a rebound hypoglycaemia.²³ Glucose resuscitates the brain but can perpetuate the cycle.
• The antidote switches the insulin off. Octreotide suppresses beta-cell insulin release, so it treats the cause rather than chasing the consequence — which is why a sulfonylurea overdose has a mechanism-directed antidote and metformin does not.²³

A sulfonylurea overdose is a hormone problem wearing a drug's name: stop thinking about the tablet and start thinking about the insulin it keeps releasing.

The toxic principle

There is one toxic principle — glucose-independent insulin release — and its three clinical consequences (delay, recurrence, and resistance to glucose alone) all follow from it.

• The drug closes the beta-cell potassium channel. Sulfonylureas bind the SUR1 subunit of the ATP-sensitive potassium channel and hold it shut; the cell depolarises, calcium enters, and insulin is released — the physiological secretory pathway, driven pharmacologically and independent of the blood glucose.¹³ Established
• So the hypoglycaemia is insulin-mediated and sustained. Because the stimulus is the drug, not a meal, insulin keeps being released even as the glucose falls — the normal off-switch is overridden.¹³ Severe reactions include coma, convulsions and other neurological disorders.¹
• And glucose can feed it. A rising glucose is itself a secretory stimulus, so correcting the sugar with dextrose can provoke more insulin and a rebound low — the reason glucose alone often fails to hold.²³ Established

Toxicokinetics

Metabolism and the metabolites

Sulfonylureas are handled by the liver, and for most of the modern agents the metabolites are inactive — gliclazide's are not detected in plasma and almost none of the drug leaves unchanged.¹ The clinically important exception is the older agents whose metabolites are themselves hypoglycaemic and are cleared by the kidney, so that the duration of toxicity depends on both the drug and renal function.

What changes the answer

• Which agent was taken — long-acting drugs and those with active metabolites cause longer, deeper hypoglycaemia.¹ Established
• Renal function — impaired clearance of active metabolites prolongs the danger for the agents that have them.¹ Inferred
• Age and size — a single tablet can drive a small child's pancreas for many hours, so paediatric ingestion is treated cautiously.²
• Co-ingestants and starvation — anything that limits the patient's own glucose reserves deepens the hypoglycaemia.

Elimination and accumulation

Sulfonylureas are cleared by hepatic metabolism, with the kidney mattering for the agents whose metabolites are active. Because they are highly protein-bound, there is no extracorporeal shortcut — the body must metabolise and excrete the drug, and the treatment has to hold the patient safe for however long that takes.

The EXTRIP position

EXTRIP has not assessed the sulfonylureas — they are absent from the workgroup's list of reviewed poisons.⁴ That absence is coherent rather than a gap: the agents are strongly protein-bound, the label states dialysis is of no benefit,¹ and there is an effective pharmacological antidote, so extracorporeal removal has neither plausibility nor a role to fill.

• Removal is not the strategy — high protein binding makes dialysis futile,¹ so unlike metformin there is no machine to remove the drug.
• Suppression is the strategy — octreotide stops the insulin release while the body clears the drug, and glucose keeps the brain supplied in the meantime.²³
• Time is the other variable — the patient must be kept safe across the drug's full duration of action, which is why a long-acting agent demands a longer observation than the first correction suggests.¹

Target organs — and why those

Timeline of effects

A sulfonylurea timeline is defined by delay and recurrence. Hypoglycaemia may not appear for hours, and once it does it returns after each correction until the drug is gone — so the shape of the illness is a series of dips, not a single event.

What the mechanism predicts at the bedside

Why glucose alone is not enough — and can backfire

Because the hypoglycaemia is driven by the patient's own insulin and a rising glucose is itself a secretory stimulus, a dextrose bolus can provoke another surge of insulin and a rebound low.²³ Glucose is essential to protect the brain, but used alone it treats the symptom while feeding the mechanism — which is why it so often fails to hold and why the definitive move is to switch the insulin off. Established

Why octreotide is a real antidote, not a tonic

Octreotide suppresses beta-cell insulin secretion, acting directly on the release the sulfonylurea is driving.²³ It addresses the defined lesion — glucose-independent hyperinsulinism — rather than its consequence, which is the hallmark of a mechanism-directed antidote. The paediatric NPDS series showed it reduced hypoglycaemic episodes and raised the lowest glucose, with most children needing only one dose;² a toxicology review concluded there is sufficient animal and human evidence to recommend octreotide with supplemental dextrose for sulfonylurea-induced hypoglycaemia.³ Established

Why dialysis has no role

Sulfonylureas are strongly protein-bound — gliclazide about 95% — so very little drug is free to be removed, and the label states plainly that dialysis is of no benefit.¹ This is the exact inverse of metformin, whose negligible binding makes it readily dialysable, and it is why the two diabetic overdoses demand opposite strategies: remove the one, suppress the other.

Why the observation outlasts the first correction

The drug keeps releasing insulin for as long as it is present, and its half-life (and any active metabolite) can be long.¹ So the period of danger is the drug's duration, not the time to the first normal glucose — and a discharge timed to the latter is a discharge into a recurrence.

The antidote, from the poison's side

A sulfonylurea overdose has a true mechanism-directed antidote, and it works one step downstream of the drug. Octreotide does not remove the sulfonylurea or block its channel; it suppresses the insulin release the drug is provoking, turning off the output rather than the input.

• Octreotide suppresses the sulfonylurea-driven insulin, breaking the cycle of recurrent hypoglycaemia at its source.²³ It is the treatment the mechanism predicts, and it reduces both the number of hypoglycaemic episodes and the glucose requirement.² Established
• Glucose protects the brain but does not fix the cause, and can re-stimulate insulin if used alone;²³ the two are complementary — dextrose to keep the patient safe now, octreotide to stop the insulin that keeps pulling the glucose down.
• Dialysis does nothing, because the drug is too highly protein-bound to remove.¹ There is no extracorporeal option to fall back on, which makes the antidote and time the whole of the definitive treatment.
• The endpoint is the drug's clearance, not a single normal reading — octreotide and glucose hold the line until the sulfonylurea has been metabolised and excreted.¹

Critical appraisal

1. The endogenous-insulin mechanism is well established and clinically load-bearing.¹³ It explains the delay, the recurrence, the glucose trap and the choice of octreotide, and the inappropriately high insulin and C-peptide confirm it at the bench. This is the firmest ground on the page.
2. The glucose-rebound phenomenon is mechanistically sound and clinically observed Established — a rising glucose is a known secretory stimulus, and the recurrent dips after dextrose boluses are the everyday expression of it.²³ It is the single most useful counter-intuitive fact here.
3. The octreotide evidence is real but not high-tier. The strongest single study cited is a retrospective NPDS series in children,² supported by a narrative toxicology review that also weighs animal and case data.³ The direction of effect is consistent and the mechanism is sound, but these are not large randomised trials, and the page presents octreotide as well-founded rather than definitively proven. Inferred
4. Gliclazide is an exemplar, and the class is heterogeneous. The kinetics quoted are gliclazide's;¹ agents such as glibenclamide have active, renally-cleared metabolites that make hypoglycaemia longer and deeper, so the page's duration figures are representative, not universal. An auditor should read the kinetics as 'gliclazide, and more for some'.
5. The EXTRIP absence is argued, not assumed.⁴ High protein binding, an explicit statement that dialysis does not help, and an effective antidote together make extracorporeal treatment implausible, so the workgroup's silence is coherent — the same reasoning the library applies to other non-dialysable poisons.
6. The no-hypoglycaemia contrast with metformin is the organising device and is accurate, but it is a teaching frame: the two drugs are not opposites in nature, only in the dominant face of their overdose. The page uses the contrast to fix attention on the right number for each, not to claim a deeper symmetry.

References

1. 1
   Diamicron 80 mg Tablets (gliclazide) — Summary of Product Characteristics, Servier. emc product 1150. §4.9 and §5.2 fetched and read in full. Source of the statement that sulfonylurea overdose causes hypoglycaemia with severe reactions including coma and convulsions, that hypoglycaemic coma is treated with concentrated then dilute intravenous glucose, that dialysis is of no benefit because of the strong protein binding, the approximately 95% protein binding, the 2–6 h peak, the ~19 L volume of distribution, the absence of active metabolites in plasma with <1% excreted unchanged, and the 10–12 h elimination half-life. Verified 13 Sep 2026.
2. 2
   Dougherty PP, Lee SC, Lung D, Klein-Schwartz W. Evaluation of the use and safety of octreotide as antidotal therapy for sulfonylurea overdose in children. Pediatr Emerg Care 2013;29(3):292–5. PubMed 23426239. Retrospective National Poison Data System series of 121 children under six. Source of the reduction in hypoglycaemic episodes (median 2.0 before treatment to 0.0 after), the higher lowest blood glucose after octreotide, and the finding that 73% required only a single dose with no documented adverse effects. Verified 13 Sep 2026 from the abstract.
3. 3
   Glatstein M, Scolnik D, Bentur Y. Octreotide for the treatment of sulfonylurea poisoning. J Med Toxicol 2010;6(2):199–206. PubMed 20352540. Narrative review of animal studies, case reports, case series and controlled trials. Source of the conclusion that there is sufficient evidence to recommend octreotide with supplemental dextrose for sulfonylurea-induced hypoglycaemia, and of the account of octreotide suppressing beta-cell insulin release. Verified 13 Sep 2026 from the abstract.
4. 4
   EXTRIP Workgroup — recommendations index. extrip-workgroup.org/recommendations. Consulted 13 Sep 2026 to confirm that the sulfonylureas are not among the poisons the workgroup has assessed — they do not appear on the published list of reviewed agents. Cited here for that absence, which is coherent with the drugs' high protein binding and the availability of an effective antidote.
5. 5
   TOXBASE — gliclazide; sulfonylureas. National Poisons Information Service. toxbase.org (NHS login required. NPIS: 0344 892 0111. The authoritative UK source for glucose regimens, octreotide indications and dosing, and observation and discharge criteria. Login-gated, so not quoted here.)