Calcium Gluconate

What It Is

Calcium gluconate is a calcium salt of gluconic acid, available as a 10% solution (100 mg/mL). Each 10 mL ampule contains:

1,000 mg of calcium gluconate
~90-93 mg of elemental calcium (0.22 mmol elemental Ca per mL)

It is the preferred IV calcium formulation over calcium chloride because it is less irritating to veins and can be safely administered through a peripheral IV line - calcium chloride can cause tissue necrosis on extravasation and requires a central line. Both have equivalent efficacy and onset of action.

Mechanism of Action

Directly replenishes serum calcium levels
In hyperkalemia: calcium raises the action potential threshold to a less negative value, restoring the normal 15 mV difference between resting and threshold potentials - this reduces myocyte excitability and stabilizes the myocardium (Brenner and Rector's The Kidney)
In hypermagnesemia: antagonizes the neuromuscular blockade caused by excess magnesium

Indications

Condition	Role
Symptomatic hypocalcemia	First-line IV treatment
Hyperkalemia	First-line cardiac membrane stabilization
Hypermagnesemia	Reverses cardiac/neuromuscular toxicity
Hydrofluoric acid burns	Neutralizes fluoride ions (topical gel or infiltration)
Oxalate poisoning	Antidote - converts oxalate to insoluble calcium oxalate
Cardiac arrest (when due to hyperkalemia/hypocalcemia/hypermagnesemia)	Empiric use

Dosing

Acute symptomatic hypocalcemia (IV):

Initial: 1-2 g (10-20 mL of 10%) in 50 mL D5W over 10-20 minutes
Maintenance infusion: 0.3-1.0 mg elemental Ca/kg/hour
Mild/moderate (asymptomatic): 1-2 g IV every 4 hours without continuous infusion

Hyperkalemia (cardiac stabilization):

10 mL of 10% calcium gluconate IV over 2-3 minutes under continuous ECG monitoring
Onset: 1-3 minutes; Duration: 30-60 minutes
Repeat if no ECG improvement or if changes recur
Caution in digoxin toxicity: infuse slowly (10 mL in 100 mL D5W over 20-30 minutes) to avoid hypercalcemia potentiating digitalis toxicity

Pediatric (severe hyperkalemia): 50-100 mg/kg IV/IO

Symptomatic hypocalcemia (anesthesia): 10-20 mL of 10% at rate of 5 mL/min

(Washington Manual of Medical Therapeutics; Brenner and Rector's The Kidney; Miller's Anesthesia)

Hepatic Metabolism - Clarification

There was historical debate about whether calcium gluconate requires hepatic metabolism to release ionized calcium. In vitro studies and studies in humans (including during the anhepatic stage of liver transplantation) have confirmed that ionized calcium release from calcium gluconate is independent of hepatic metabolism and occurs rapidly - equal to that of calcium chloride. (Brenner and Rector's The Kidney)

Important Cautions

Do NOT mix with phosphates or bicarbonates in the same IV line (precipitates form)
Check serum phosphorus before giving calcium - in severe hyperphosphatemia (>6.5 mg/dL), calcium administration raises the calcium-phosphorus product and can worsen ectopic calcifications; dialysis may be needed first
Treat hypomagnesemia first - hypocalcemia cannot be effectively corrected if magnesium is low
Digoxin users: hypercalcemia potentiates digitalis toxicity - use cautiously and infuse slowly
Monitor serum calcium and ECG during infusion

Oral Calcium Supplements (Comparison)

For chronic/mild hypocalcemia, oral agents are used instead:

Calcium carbonate - 40% elemental calcium
Calcium acetate - 25% elemental calcium
Calcium gluconate - lower elemental calcium content, less commonly used orally
Goal: 1-2 g elemental calcium PO three times daily, given away from meals to maximize absorption and minimize binding with phosphorus

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