Calcium gluconate is the first-line drug for magnesium toxicity rescue. Its core mechanism lies in the "competitive antagonism between calcium and magnesium ions," which rapidly reverses the toxic effects of excess magnesium on the neuromuscular and cardiovascular systems. Clinical application must strictly follow the principles of "first diagnose and classify severity, then administer precise dosing, and conduct dynamic monitoring throughout," with specific guidelines as follows:
I. Core Mechanism of Action: Competitive Antagonism Between Calcium and Magnesium Ions
Excess magnesium ions (serum magnesium > 2.5 mmol/L indicates hypermagnesemia; > 4 mmol/L causes toxic symptoms) inhibit neuromuscular junction transmission (leading to muscle weakness, respiratory depression) and reduce cardiomyocyte excitability (triggering arrhythmia, hypotension). Calcium ions in calcium gluconate compete with magnesium ions for binding to cell membrane receptors (e.g., calcium channels at neuromuscular junctions, calmodulin in cardiomyocytes). Meanwhile, they directly enhance myocardial contractility and restore neuromuscular excitability, achieving "immediate detoxification"—symptoms can be relieved within minutes after intravenous administration. However, sustained maintenance of serum calcium concentration is required to consolidate the antagonistic effect and prevent recurrence of toxicity.
II. Precondition for Clinical Application: Confirming Magnesium Toxicity Diagnosis and Severity
Before medication, magnesium toxicity must be confirmed through "symptoms + serum magnesium testing," and treatment plans formulated based on severity to avoid blind medication:
Mild toxicity: Serum magnesium 2.5–4.0 mmol/L, manifested as nausea, vomiting, fatigue, and diminished tendon reflexes. Close monitoring is the main approach; if the patient has normal renal function, intravenous fluid replacement (e.g., normal saline) can promote magnesium excretion, and calcium gluconate is not urgently needed.
Moderate toxicity: Serum magnesium 4.0–7.0 mmol/L, accompanied by muscle weakness, dyspnea, hypotension, and bradycardia. Intravenous calcium gluconate must be administered immediately to quickly relieve core toxic symptoms and prevent disease progression.
Severe toxicity: Serum magnesium > 7.0 mmol/L, associated with respiratory paralysis, atrioventricular block, or even cardiac arrest. Emergency intravenous push of calcium gluconate is required, combined with respiratory support (e.g., ventilator-assisted ventilation) and blood purification (e.g., hemodialysis to accelerate magnesium ion clearance) to save lives.
III. Specific Medication Regimen: Preparation Selection, Dosage, and Administration Route
Calcium gluconate is mainly administered intravenously (oral absorption is slow and cannot take effect quickly). Dosage must be adjusted according to toxicity severity, and the drug must be diluted with glucose injection to avoid vascular irritation from high concentrations:
1. Common Preparation
The preferred preparation is 10% calcium gluconate injection, with each 10 mL containing 1 g of calcium gluconate (equivalent to 90 mg of calcium, approximately 2.25 mmol). It must be diluted with 5%–10% glucose injection before use.
2. Adult Dosage and Infusion Rate
Moderate Toxicity
Initial dose: Take 10–20 mL of 10% calcium gluconate, dilute with 20–40 mL of 5% glucose injection, and administer via slow intravenous push at a rate not exceeding 2 mL/min (the entire process takes approximately 10–20 minutes).
Subsequent adjustment: If symptoms do not relieve after push (e.g., tendon reflexes not restored, blood pressure still low), an additional 10 mL can be given repeatedly after 30 minutes. The total dose within 24 hours should not exceed 100 mL to prevent excessive calcium accumulation.
Severe Toxicity (Including Risk of Cardiac Arrest)
Emergency rescue: Take 20–30 mL of 10% calcium gluconate, dilute with 10–20 mL of 5% glucose injection, and administer via rapid intravenous push at a rate of 1–2 mL/min (simultaneous ECG monitoring is required to avoid arrhythmia caused by sudden increase in serum calcium).
Maintenance therapy: After symptom relief, switch to 30–50 mL of 10% calcium gluconate added to 500 mL of 5% glucose injection, and administer via intravenous infusion at a rate of 1–2 mL/min for 4–6 hours. Maintain serum calcium at 2.0–2.5 mmol/L (upper limit of normal range).
3. Pediatric Dosage Adjustment
Dosage is calculated by body weight: 20–50 mg/kg per dose (based on calcium gluconate), diluted with 5% glucose injection to 10–20 mL. Intravenous push rate should not exceed 1 mL/min; if necessary, it can be repeated every 4–6 hours. The total dose within 24 hours should not exceed 1 g/kg to avoid kidney damage from excess.
IV. Key Monitoring During Medication: Preventing Complications
During the rescue process with calcium gluconate, dynamic monitoring of the following indicators is required to avoid "overcorrection" leading to hypercalcemia or other risks:
Vital sign monitoring: Monitor heart rate, blood pressure, and respiration every 5–10 minutes. If adult heart rate < 60 beats/min or pediatric heart rate < 80 beats/min, slow down the infusion rate or pause administration; if respiration < 12 breaths/min, check for respiratory depression and initiate ventilator support if necessary.
Serum ion monitoring: Test serum magnesium and serum calcium before medication, 1 hour after medication, and 4 hours after medication. Serum magnesium only needs to be reduced to below 2.5 mmol/L (mild toxicity range), and excessive reduction is unnecessary; serum calcium should be maintained at 2.0–2.5 mmol/L. If serum calcium > 2.75 mmol/L (hypercalcemia), immediately stop medication and use furosemide (to promote calcium excretion).
ECG monitoring: Continuous ECG monitoring is required for severe toxicity or intravenous push. If "QT interval shortening" or "atrioventricular block" (typical manifestations of hypercalcemia) occurs, immediately stop medication to avoid cardiac damage.
V. Contraindications and Precautions: Avoiding Medication Risks
Absolute contraindications: Contraindicated in patients allergic to calcium gluconate, patients with hypercalcemia/hypercalciuria, and patients using cardiac glycosides (e.g., digoxin). For the latter, increased serum calcium enhances cardiac glycoside toxicity, which may induce severe arrhythmia.
Special populations for cautious use: Renal insufficiency patients need dosage reduction (impaired calcium excretion ability may lead to accumulation); elderly patients need slower infusion rate to avoid sudden hypotension; dehydrated patients need fluid replacement before medication to prevent excessive calcium concentration.
Administration contraindications: Intramuscular or subcutaneous injection is prohibited (high-concentration calcium causes local tissue necrosis); intravenous push must not be too fast to avoid sudden increase in serum calcium leading to cardiac arrest.
The core of calcium gluconate for magnesium toxicity rescue is "rapid antagonism + precise dosage control." It is necessary to first classify severity based on symptoms and serum magnesium, then select the corresponding dosage and administration route, and conduct dynamic monitoring of vital signs, serum ions, and ECG throughout the process. Meanwhile, contraindicated populations and improper administration routes should be avoided to achieve effective detoxification while reducing the risk of complications.
