Calcium Salts
Calcium salts are essential mineral supplements used primarily to treat or prevent **hypocalcemia** and as oral phosphorus-binding agents in patients with renal failure. Parenteral calcium is a critical emergency drug used for: * **Documented ionized hypocalcemia** (e.g., eclampsia/puerperal tetany, primary hypoparathyroidism). * **Hyperkalemic cardiotoxicity** (e.g., blocked cats, Addisonian crisis). *Clinical Pearl: Calcium does not lower serum potassium; rather, it raises the threshold potential of the myocardium, restoring the normal resting-to-threshold gap and protecting the heart from fatal arrhythmias.* * **Calcium channel blocker toxicity**. **Clinical Pearl:** It is crucial to distinguish between calcium salts. **Calcium chloride 10%** contains approximately three times the amount of elemental calcium (27.2 mg/mL) compared to **Calcium gluconate 10%** (9.3 mg/mL). Calcium chloride is highly irritating, acidifying, and carries a severe risk of tissue necrosis if extravasated; it should ideally be given via a central line. Calcium gluconate is the preferred salt for peripheral IV administration.
Mechanism: Calcium is an essential intracellular and extracellular cation vital for numerous physiological processes: * **Nervous and Musculoskeletal Function:** Facilitates excitation-contraction coupling in cardiac and smooth muscle, and is required for neurotransmitter release at synaptic clefts. * **Cell Membrane Permeability:** Maintains cell membrane integrity and capillary permeability. * **Enzymatic Reactions:** Acts as a crucial cofactor for various enzymatic reactions and the coagulation cascade. * **Hyperkalemia Antagonism:** In hyperkalemia, elevated resting membrane potentials lead to cardiac conduction blocks. Calcium administration **โ** raises the threshold potential **โ** restores the normal electrical gradient **โ** stabilizes the myocardium.
Dosing by species
- Hypocalcemia ยท 150-250 mg/kg IV slowly to effect ยท IV ยท PRN ยท Intraperitoneal route may also be used. Monitor respirations and cardiac rate and rhythm.
- Hypocalcemia ยท Calcium gluconate 23% injection: 25-50 mL IV slowly, or IM or SC (divided and given in several locations, with massage at sites of injection) ยท IV/IM/SC ยท PRN
- Hypocalcemia ยท 150-250 mg/kg IV slowly to effect ยท IV ยท PRN ยท Dosing extrapolated from sheep guidelines. Intraperitoneal route may also be used.
- Hypocalcemia ยท Calcium gluconate 23% injection: 25-50 mL IV slowly, or IM or SC (divided and given in several locations, with massage at sites of injection) ยท IV/IM/SC ยท PRN ยท Dosing extrapolated from sheep guidelines.
- Hypocalcemia ยท 94-140 mg/kg IV slowly to effect ยท IV ยท PRN ยท Intraperitoneal route may also be used. Monitor respirations and cardiac rate and rhythm.
- Acute hypocalcemia secondary to hypoparathyroidism ยท 10% calcium gluconate injection, give 1-1.5 mL/kg IV slowly over 10-20 minutes. Once controlled, add to IV fluids as slow infusion at 60-90 mg/kg/day (of elemental calcium) [converts to 2.5 mL/kg every 6-8 hours of 10% calcium gluconate]. Oral: initially 50-100 mg/kg/day divided 3-4 times daily of elemental calcium. ยท IV/PO ยท PRN/CRI/Divided ยท Monitor ECG. If bradycardia or Q-T interval shortening occurs, slow rate or temporarily discontinue.
- Hypocalcemia secondary to phosphate enema toxicity or puerperal tetany ยท 10% calcium gluconate injection, give 1-1.5 mL/kg IV slowly over 10-20 minutes. ยท IV ยท PRN ยท Follow guidelines for use of intravenous calcium.
Routes of administration
Contraindications
- Ventricular fibrillation
- Hypercalcemia
Adverse effects
- Hypercalcemia
- GI irritation and/or constipation (oral administration)
- Mild to severe tissue reactions, pyogranulomatous panniculitis, adipocyte mineralization (IM or SC administration)
- Venous irritation (IV administration)
- Hypotension (if given IV too rapidly)
- Cardiac arrhythmias and cardiac arrest (if given IV too rapidly)
Drug interactions
- Calcium Channel Blockers (e.g., diltiazem, verapamil) ยท Intravenous calcium may antagonize the effects of calcium-channel blocking agents.
- Digoxin ยท Patients on digitalis therapy are more apt to develop arrhythmias if receiving IV calcium; use with extreme caution.
- Magnesium (oral) ยท May lead to increased serum magnesium and/or calcium, particularly in patients with renal failure.
- Magnesium Sulfate (parenteral) ยท Parenteral calcium can neutralize the effects of hypermagnesemia or magnesium toxicity secondary to parenteral magnesium sulfate.
- Neuromuscular Blockers (e.g., atracurium, vecuronium, tubocurarine) ยท Parenteral calcium may reverse the effects of nondepolarizing neuromuscular blocking agents; has been reported to prolong or enhance the effects of tubocurarine.
- Tetracyclines, Fluoroquinolones (oral) ยท Oral calcium can reduce the amount of these antibiotics absorbed from the GI tract via chelation; separate dosages by at least two hours.
- Potassium Supplements ยท Patients receiving both parenteral calcium and potassium supplementation may have an increased chance of developing cardiac arrhythmias.
- Thiazide Diuretics ยท Used in conjunction with large doses of calcium may cause hypercalcemia.
- Vitamin A ยท Excessive intake may stimulate calcium loss from bone and cause hypercalcemia.
- Vitamin D ยท Concurrent use of large doses of vitamin D or its analogs may cause enhanced calcium absorption and induce hypercalcemia.
Monitoring
- Serum calcium (total and ionized)
- Serum magnesium, phosphate, and potassium
- Serum PTH (parathormone) if indicated
- Renal function tests
- ECG and heart rate (continuously during IV therapy)
- Urine calcium (if hypercalciuria develops)
Overdose
Oral overdoses of calcium-containing products are unlikely to cause hypercalcemia unless other drugs (e.g., Vitamin D) are given concurrently that enhance absorption. **Hypercalcemia** can occur with parenteral therapy or oral therapy combined with Vitamin D or increased PTH levels. * **Mild hypercalcemia:** Generally resolves without intervention when renal function is adequate. Withhold calcium therapy and Vitamin D analogs. * **Serious hypercalcemia (>12 mg/dL):** Treat by hydrating with IV normal saline and administering a loop diuretic (e.g., **furosemide**) to increase sodium and calcium excretion. Monitor and replace potassium and magnesium as necessary. Monitor ECG. Corticosteroids, calcitonin, and hemodialysis may also be employed.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.