Calcium (antidote)

#complete #carded

Related FACEM curriculum (2022) learning objectives:

• ME 3.8.1.6(e) Principles of management of toxicological presentations including: Indications for antidotes
• ME 3.8.2.4 Identify the appropriate antidote or antivenom.

Presentations

• Calcium gluconate:
  • 1 g/10 mL vials (0.22 mmol calcium ions/mL).
  • 5 g/50 mL vials (0.22 mmol calcium ions/mL).
• Calcium chloride:
  • 0.74 g/5 mL ampoules (1.01 mmol calcium ions/mL).
  • 1 g/10 mL ampoules or syringes (0.68 mmol calcium ions/mL).

Toxicological Indications

• Calcium channel blocker poisoning.
• Hydrofluoric acid exposure (skin, inhalation, systemic fluorosis).
• Hypocalcaemia due to fluorosis or ethylene glycol poisoning.
• Iatrogenic hypermagnesaemia.
• Hyperkalaemia.

Contraindications

• Hypercalcaemia.
• Digoxin toxicity (controversial).

Mechanism of Action

• Antagonises hyperkalaemia and hypermagnesaemia effects on cardiac conduction and skeletal muscle.
• Restores ionised calcium in hypocalcaemic states to prevent dysrhythmias.
• Binds fluoride ions in hydrofluoric acid poisoning, preventing tissue damage.
• Elevates ionised calcium to counteract calcium channel blocker poisoning.

Pharmacokinetics

• 99% of calcium is in bones.
• Plasma calcium: 50% ionised (active), 50% bound to albumin.
• Plasma calcium is maintained ~2.5 mmol/L via hormonal regulation.

Administration

General

• Monitor patient with resuscitative support available.
• Cardiac monitoring mandatory during calcium salt infusion.

Hypocalcaemia/Hyperkalaemia/Hypermagnesaemia

• 0.5–1 g (5–10 mL) calcium chloride or 1–2 g (10–20 mL) calcium gluconate IV over 5–10 minutes.
• Repeat every 10–15 minutes as required.
• Adjust dosing based on serum calcium levels (avoid hypercalcaemia).

Calcium Channel Blocker Poisoning

• 2 g (20 mL) calcium chloride IV or 6 g (60 mL) calcium gluconate IV over 5–10 minutes.
• Repeat every 20 minutes for up to 3 doses.

Hydrofluoric Acid Skin Exposure

• Topical 2.5% calcium gel for minor burns (apply in glove for hand burns).
• Intradermal calcium gluconate (0.5 mL/cm² using 1 g/10 mL solution) if pain persists.
• Bier's block for finger/hand/forearm burns:
  • Dilute 1 g (10 mL) calcium gluconate in 40 mL normal saline.
  • Administer via intravenous tourniquet; release cuff after 20 minutes.
• Intra-arterial infusion: Dilute 1 g (10 mL) calcium gluconate in 40 mL saline; infuse over 4 hours.

Hydrofluoric Acid Inhalation

• Nebulise 2.5% calcium gluconate solution.

Therapeutic Endpoints

• Hypocalcaemia/Hypermagnesaemia/Hyperkalaemia: Normalisation of serum calcium.
• Calcium channel blocker poisoning: Haemodynamic improvement.
• Hydrofluoric acid exposure: Pain resolution.

Adverse Drug Reactions

• Transient hypercalcaemia (tetany, seizures): Stop calcium administration and check serum calcium.
• Over-rapid administration: Vasodilation, hypotension, dysrhythmias, syncope, cardiac arrest.
  • Manage with resuscitative support.
• Local tissue damage from calcium chloride extravasation.

Specific Considerations

• Pregnancy: No restrictions.
• Paediatric Dose: 1 mL/kg 10% calcium gluconate solution over 5–10 minutes; repeat every 10–15 minutes as needed.

Handy Tips

• QT duration and hypocalcaemia symptoms are better guides than serum calcium for dosing.
• Calcium gluconate is safer for peripheral lines; calcium chloride is preferred via central lines due to extravasation risks.
• Avoid mixing calcium salts with sodium bicarbonate in the same IV line.
• Hydrofluoric acid gel preparation:
  • Mix 10 mL 10% calcium gluconate with 30 mL lubricant gel (e.g., K-Y jelly).
  • Alternative: 3.5 g calcium gluconate powder with 150 mL lubricant gel.
• Do not irrigate eyes with calcium salt solutions to avoid corneal injury.
• Persistent pain after calcium therapy in late hydrofluoric acid burns suggests tissue damage.

Controversies

• Optimal dosing and efficacy of calcium salts in calcium channel blocker poisoning.
• Best route for calcium salt administration in hydrofluoric acid skin burns.