Makindo Medical Notes

💡 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.

📘 About: Always check the BNF link here

• Glucagon is a 29–amino acid polypeptide hormone secreted by pancreatic α-cells.
• It raises blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis.
• Also exerts potent inotropic and chronotropic effects on the heart independent of β-adrenergic receptors — hence its use in beta-blocker and calcium channel blocker overdose.

⚙️ Mode of Action

• Binds to glucagon Gs-protein-coupled receptors → increases intracellular cAMP.
• In hepatocytes: stimulates glycogen breakdown and glucose release into the bloodstream.
• In the heart: increases cAMP directly (bypassing β-receptors), enhancing contractility and heart rate even when β-receptors are blocked.
• Short half-life (8–18 minutes); effect transient unless supported by glucose or infusion.

🎯 Indications

• Severe hypoglycaemia (when IV access is delayed or impossible).
• β-blocker overdose causing bradycardia or hypotension.
• Calcium channel blocker overdose causing myocardial depression or cardiogenic shock.

💊 Indications and Doses

⚠️ 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.

💥 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.

🧠 Teaching Point

Glucagon illustrates how hormone-based physiology is leveraged in emergency medicine. In hypoglycaemia, it mobilises hepatic glycogen reserves to restore glucose; in β-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.

📚 References

• BNF: Glucagon
• Resuscitation Council UK 2021 Guidelines
• AHA Case Series: Glucagon in β-blocker Overdose