๐ก Key point: Glucagon is life-saving in severe hypoglycaemia and beta-blocker or calcium channel blocker toxicity.
However, it will not work in malnourished or cachectic patients with depleted hepatic glycogen - such patients require IV glucose instead.
- Glucagon is a 29โamino acid polypeptide hormone secreted by pancreatic ฮฑ-cells.
- It raises blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis.
- Also exerts potent inotropic and chronotropic effects on the heart independent of ฮฒ-adrenergic receptors - hence its use in beta-blocker and calcium channel blocker overdose.
โ๏ธ Mode of Action
- Binds to glucagon Gs-protein-coupled receptors โ increases intracellular cAMP.
- In hepatocytes: stimulates glycogen breakdown and glucose release into the bloodstream.
- In the heart: increases cAMP directly (bypassing ฮฒ-receptors), enhancing contractility and heart rate even when ฮฒ-receptors are blocked.
- Short half-life (8โ18 minutes); effect transient unless supported by glucose or infusion.
๐ฏ Indications
- Severe hypoglycaemia (when IV access is delayed or impossible).
- ฮฒ-blocker overdose causing bradycardia or hypotension.
- Calcium channel blocker overdose causing myocardial depression or cardiogenic shock.
๐ Indications and Doses
| Name / Indication | Starting Dose | Frequency / Notes | Route |
|---|
| Hypoglycaemia (Adults & Children โฅ25kg) |
1 mg (1 unit) stat |
May repeat after 15 min if needed; give oral or IV glucose as soon as possible to replenish stores. |
IM / SC / IV |
| Severe Hypoglycaemia (Children <25kg) |
0.5 mg stat |
Repeat if necessary; ensure follow-up carbohydrate intake once conscious. |
IM / SC / IV |
| ฮฒ-blocker / CCB toxicity (Cardiogenic shock) |
Initial 2โ10 mg IV bolus in 5% glucose (protect airway - risk of vomiting) |
Follow with continuous IV infusion at 50 ยตg/kg/hour (typically 1โ5 mg/hour).
๐ฌ AHA guidance: One case series documented improvement with IV glucagon (3 mg bolus โ infusion 3 mg/h) in drug-induced bradycardia unresponsive to atropine. |
IV bolus then infusion |
โ ๏ธ Contraindications
- Phaeochromocytoma - glucagon can precipitate hypertensive crisis due to catecholamine release.
- Cachexia or malnutrition - ineffective if hepatic glycogen depleted.
- Insulinoma - may exacerbate hypoglycaemia via paradoxical insulin release.
๐ฅ Side Effects
- Nausea and vomiting (common) - protect airway if unconscious.
- Transient hyperglycaemia and mild hypokalaemia.
- Occasional hypotension, dizziness, or headache.
- Rare: allergic reaction or rash at injection site.
๐ง Teaching Point
Glucagon illustrates how hormone-based physiology is leveraged in emergency medicine.
In hypoglycaemia, it mobilises hepatic glycogen reserves to restore glucose; in ฮฒ-blocker and CCB overdose, it restores cardiac contractility via a cAMP-mediated mechanism independent of adrenergic receptors.
Understanding these distinct mechanisms helps explain why glucagon succeeds when adrenaline and atropine may fail - and why it fails when hepatic glycogen is depleted.
๐ References
