calcium carbonate
Calcium supplement, antacid· Brands: Tums, Caltrate, Os-Cal, Titralac, RolaidsPO
Mechanism of action
Calcium carbonate neutralises gastric acid by raising intragastric pH, providing rapid relief of dyspepsia. It also supplies elemental calcium, and in the bowel binds phosphate, reducing absorption and lowering serum phosphate.
Pharmacokinetics
Absorption of calcium from calcium carbonate requires an acidic environment; dissolution and absorption are impaired in achlorhydria or with concurrent acid-suppressant therapy. Onset of antacid effect is prompt, while calcium absorption is saturable. Excretion is predominantly faecal for unabsorbed calcium, with absorbed calcium eliminated via the kidneys.
Indications & dosing
Acid indigestion and heartburn
Chewable tablets. Take after meals and at bedtime. Do not exceed 2 weeks of self-treatment without clinical advice.
- adult · PO: 500–1000 mg PRN · Chewable tablets. Take after meals and at bedtime. Do not exceed 2 weeks of self-treatment without clinical advice.
Calcium supplementation (e.g., osteoporosis prevention, dietary deficiency)
Take with food to enhance absorption. 1250 mg provides 500 mg elemental calcium.
- adult · PO: 1250–2500 mg 1-2 times daily · Take with food to enhance absorption. 1250 mg provides 500 mg elemental calcium.
Hyperphosphataemia in chronic kidney disease (phosphate binder)
Adjust dose according to serum phosphate levels. Monitor for hypercalcaemia and vascular calcification.
- adult · PO: 1000–2000 mg TID with meals · Adjust dose according to serum phosphate levels. Monitor for hypercalcaemia and vascular calcification.
Contraindications & precautions
- Hypercalcaemia · Calcium carbonate increases serum calcium; use is contraindicated in existing hypercalcaemia.
- Hypercalciuria · Excretion of calcium is increased, worsening calcium loss in urine.
- Renal calculi · Calcium-containing stones may worsen with increased calcium excretion.
- Severe renal impairment · Risk of hypercalcaemia and milk-alkali syndrome; monitor closely if used.
- Monitor serum calcium and renal function during prolonged therapy.
- Use with caution in patients with renal impairment or a history of renal stones.
- Avoid concurrent use with thiazide diuretics or vitamin D, as this may increase hypercalcaemia risk.
- Administer with food to enhance absorption, but separate from iron, tetracyclines, and fluoroquinolones by at least 2 hours.
Adverse effects
- Constipation
- Flatulence
- Nausea
- Hypercalcaemiaserious
- Milk-alkali syndromeserious
Interactions
- levothyroxinemoderateAdminister levothyroxine and calcium carbonate at least 4 hours apart to avoid the interaction. This can be achieved by taking levothyroxine on an empty stomach and calcium carbonate with meals or at a different time of day. Monitor TSH levels approximately 6 to 8 weeks after any change in the dosing schedule or the introduction or discontinuation of calcium carbonate, and adjust the levothyroxine dose as needed.
Renal & hepatic adjustment
- eGFR 0–29: Use with caution. Monitor serum calcium and phosphate closely. Avoid if hypercalcaemia or evidence of vascular calcification. Consider non-calcium-containing phosphate binders where possible.
- eGFR 30–60: No specific dose adjustment required, but monitor serum calcium periodically to avoid hypercalcaemia.
Monitoring, pregnancy & toxicity
- Serum calcium · Baseline and periodically during treatment
- Serum phosphate · If used as a phosphate binder
- Renal function (serum creatinine/eGFR) · Baseline and periodically
- Urinary calcium excretion · In long-term high-dose therapy
- Signs and symptoms of hypercalcaemia · Monitor clinically (e.g., polyuria, constipation, confusion)
- Pregnancy: Calcium carbonate is generally considered safe in pregnancy at recommended doses. It is commonly used for calcium supplementation and as an antacid. Ensure total daily calcium intake does not exceed the recommended limit to avoid hypercalcaemia.
- Toxicity: Hypercalcaemia: nausea, vomiting, polyuria, constipation, confusion, bone pain, renal stones in chronic use. · Stop calcium carbonate, maintain hydration, correct electrolyte imbalances. In severe hypercalcaemia, give IV sodium chloride 0.9%, and consider calcitonin or bisphosphonates as per local protocols.
- Toxicity: Milk-alkali syndrome: hypercalcaemia, metabolic alkalosis, and renal impairment, particularly with high doses and coexisting renal disease. · Discontinue calcium carbonate, provide IV fluids, and monitor renal function. Adjust treatment of calcium and acid-base disturbances as clinically indicated.
Clinical notes
Used for symptomatic relief of dyspepsia, as a calcium supplement in deficiency, and as a phosphate binder in chronic kidney disease. Doses vary by indication. Monitor for hypercalcaemia, constipation, and milk-alkali syndrome. Caution in renal impairment and with calcium-containing or vitamin D preparations. Administer with food to optimise absorption.
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BNF; local formulary