The information provided in this article is intended for educational purposes only and is aimed at healthcare professionals. While every effort has been made to ensure the accuracy and completeness of the information presented, it is not a substitute for professional medical advice, diagnosis, or treatment. Medical professionals should rely on their clinical expertise and judgement when interpreting and applying the information. The authors and publishers of this article are not liable for any errors or omissions or for any outcomes related to the use of this information. Always consult relevant guidelines, standards, and peer-reviewed sources for comprehensive and up-to-date information.
Description
Glucagon is not only a hormone involved in glucose metabolism but also serves as an effective antidote in cases of severe beta-blocker overdose. Beta-blockers are medications that reduce heart rate, blood pressure, and myocardial contractility, and an overdose can lead to life-threatening bradycardia, hypotension, and cardiogenic shock. Glucagon helps to counteract these effects due to its unique mechanism of action that bypasses the beta-adrenergic receptor pathway.
Mechanism of Action
In the context of beta-blocker overdose, glucagon works by activating adenylate cyclase via glucagon receptors on cardiac cells, independent of beta-adrenergic receptors. This activation increases intracellular cyclic AMP (cAMP) levels, which in turn enhances calcium influx into the cardiac cells. The increased intracellular calcium helps to improve myocardial contractility and heart rate, thereby reversing the negative inotropic and chronotropic effects of beta-blockers.
Side Effects
Common side effects when used as an antidote include:
- Nausea and vomiting
- Hyperglycaemia
- Hypokalaemia
- Allergic reactions (rare)
- Tachycardia and hypertension (especially in patients with preexisting cardiac conditions)
Indications
As an antidote, glucagon is indicated for:
- Severe beta-blocker overdose with symptomatic bradycardia, hypotension, or cardiogenic shock.
- Calcium channel blocker overdose (as an off-label use), given its similar ability to increase intracellular cAMP and counteract myocardial depression.
Contraindications
Absolute
- Pheochromocytoma: Risk of precipitating a hypertensive crisis due to catecholamine release.
- Insulinoma: Risk of causing severe hypoglycemia due to excessive insulin release.
Relative
- Hypersensitivity to glucagon or its components.
- Preexisting cardiovascular diseases that may be exacerbated by glucagon’s effects on heart rate and contractility.
Dosage
Adult
- In cases of beta-blocker overdose, the initial dose of glucagon is typically 3-10 mg administered intravenously over 1-2 minutes. If there is no response, additional doses may be given, or a continuous infusion may be initiated at a rate of 1-5 mg/hour based on the patient’s clinical response.
Paediatrics
- For paediatric patients with beta-blocker overdose, the recommended initial dose is 0.03-0.1 mg/kg (maximum dose of 1 mg) administered intravenously over 1-2 minutes. If there is an inadequate response, additional doses or continuous infusion at a rate of 0.05-0.1 mg/kg/hour may be considered.
Reference
Australian Medicines Handbook. (2024). Glucagon for Beta Blocker Overdose. Available at: AMH Online (Accessed: 13 July 2024).