鈣鹽（葡萄糖酸鈣、氯化鈣、乳酸鈣、葡庚糖酸鈣）
鈣鹽是必需的礦物質補充劑，主要用於治療或預防**低血鈣症**，並在腎衰竭患者中作為口服磷結合劑。 注射用鈣劑是一種關鍵的急救藥物，用於： * **確診的游離鈣低下**（例如：產後子癇症/產褥期抽搐、原發性副甲狀腺機能低下）。 * **高血鉀性心臟毒性**（例如：貓下泌尿道阻塞、愛迪生氏症危機）。*臨床要點：鈣劑並不會降低血清鉀離子濃度；相反地，它能提高心肌的閾值電位，恢復正常的靜止至閾值電位差，從而保護心臟免受致命性心律不整的影響。* * **鈣離子通道阻斷劑中毒**。 **臨床要點：** 區分不同的鈣鹽至關重要。**10%氯化鈣 (Calcium chloride)** 所含的元素鈣（27.2 mg/mL）約為 **10%葡萄糖酸鈣 (Calcium gluconate)**（9.3 mg/mL）的三倍。氯化鈣具有高度刺激性和酸化作用，若發生血管外滲漏會導致嚴重的組織壞死；理想情況下應透過中央靜脈導管給藥。葡萄糖酸鈣則是周邊靜脈注射的首選鈣鹽。
作用機制: 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 **→** raises the threshold potential **→** restores the normal electrical gradient **→** stabilizes the myocardium.
各物種劑量
- Hypocalcemia · 150-250 mg/kg IV slowly to effect · IV · PRN · Intraperitoneal route may also be used. Monitor respirations and cardiac rate and rhythm.
- Hypocalcemia · 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) · IV/IM/SC · PRN
- Hypocalcemia · 150-250 mg/kg IV slowly to effect · IV · PRN · Dosing extrapolated from sheep guidelines. Intraperitoneal route may also be used.
- Hypocalcemia · 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) · IV/IM/SC · PRN · Dosing extrapolated from sheep guidelines.
- Hypocalcemia · 94-140 mg/kg IV slowly to effect · IV · PRN · Intraperitoneal route may also be used. Monitor respirations and cardiac rate and rhythm.
- Acute hypocalcemia secondary to hypoparathyroidism · 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. · IV/PO · PRN/CRI/Divided · Monitor ECG. If bradycardia or Q-T interval shortening occurs, slow rate or temporarily discontinue.
- Hypocalcemia secondary to phosphate enema toxicity or puerperal tetany · 10% calcium gluconate injection, give 1-1.5 mL/kg IV slowly over 10-20 minutes. · IV · PRN · Follow guidelines for use of intravenous calcium.
給藥途徑
禁忌症
- Ventricular fibrillation
- Hypercalcemia
不良反應
- 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)
藥物相互作用
- Calcium Channel Blockers (e.g., diltiazem, verapamil) · Intravenous calcium may antagonize the effects of calcium-channel blocking agents.
- Digoxin · Patients on digitalis therapy are more apt to develop arrhythmias if receiving IV calcium; use with extreme caution.
- Magnesium (oral) · May lead to increased serum magnesium and/or calcium, particularly in patients with renal failure.
- Magnesium Sulfate (parenteral) · Parenteral calcium can neutralize the effects of hypermagnesemia or magnesium toxicity secondary to parenteral magnesium sulfate.
- Neuromuscular Blockers (e.g., atracurium, vecuronium, tubocurarine) · 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) · 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 · Patients receiving both parenteral calcium and potassium supplementation may have an increased chance of developing cardiac arrhythmias.
- Thiazide Diuretics · Used in conjunction with large doses of calcium may cause hypercalcemia.
- Vitamin A · Excessive intake may stimulate calcium loss from bone and cause hypercalcemia.
- Vitamin D · Concurrent use of large doses of vitamin D or its analogs may cause enhanced calcium absorption and induce hypercalcemia.
監測
- 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)
過量
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.
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