Calcium Carbonate (Calcium Carbonate)
Also sold as: Shelcal, Calcimax, Calcium Sandoz, Carbonate, Calci-D, Ossopan, Gemcal
Pregnancy
Cat A
Lactation
Safe
Schedule
OTC
Forms
Tablet 500mg (equivalent to 200mg elemental calcium) +4
Indications
- Calcium deficiency (hypocalcemia)
- Osteoporosis prevention and treatment (with vitamin D)
- Osteomalacia and rickets (adjunct to vitamin D)
- Hypoparathyroidism
- Prevention of calcium loss in menopause
- Pregnancy and lactation (increased calcium demand)
- Renal osteodystrophy — calcium carbonate used as phosphate binder (with meals)
- Heartburn / Indigestion (antacid use)
- Prophylaxis in patients on long-term corticosteroids
Adult Dosing
Calcium supplementation / Osteoporosis prevention
500–1000mg elemental calcium daily in divided doses
Long-term; with vitamin D for better absorption and bone benefit
Total dietary + supplemental calcium should not exceed 2000mg/day. Take with meals for best absorption.
Hypocalcemia (mild to moderate)
1000–1500mg elemental calcium daily in 2–3 divided doses
Until serum calcium normalizes; then maintenance
Severe acute hypocalcemia requires IV calcium gluconate, not oral supplements
Phosphate binder (CKD / Renal osteodystrophy)
500–1500mg elemental calcium WITH meals (binds dietary phosphate)
Long-term; dose titrated to serum phosphate; monitor calcium
Calcium-based phosphate binders can cause hypercalcemia in dialysis patients; sevelamer preferred if calcium already elevated
Antacid (heartburn)
500–1500mg (1–3 chewable tablets) as needed after meals / at bedtime
PRN use; avoid frequent use (acid rebound)
Postmenopausal osteoporosis (with vitamin D)
1000–1500mg elemental calcium daily (split doses) + 800–1000 IU vitamin D
Long-term
Pediatric Dosing
Most children get adequate calcium from dietary sources (dairy, fortified foods). Supplement only if dietary intake insufficient. Rickets: supplement with vitamin D primarily; calcium adjunct.
Renal Dose Adjustment
| CrCl / eGFR | Dose Adjustment |
|---|---|
| CKD stage 3–4 | Use with caution; monitor serum calcium and phosphate. May use as phosphate binder at meals but monitor for hypercalcemia. |
| CKD stage 5 / Dialysis | Limit calcium from all sources ≤1500mg/day. Risk of hypercalcemia, vascular calcification, adynamic bone disease. Consider sevelamer or lanthanum carbonate as phosphate binder if serum calcium elevated. |
Hepatic Adjustment
No specific dose adjustment required for hepatic impairment.
Pregnancy & Lactation
Pregnancy: Category A
Essential in pregnancy — fetal bone mineralization demands increase calcium needs. Recommended daily intake in pregnancy: 1000–1200mg elemental calcium. Calcium supplementation in high-risk women reduces risk of preeclampsia (WHO recommends 1.5–2g/day elemental calcium for preeclampsia prevention in low-calcium diet populations like India).
Lactation: Safe
Calcium supplementation is safe and beneficial during breastfeeding. Lactation depletes maternal calcium — supplementation helps maintain bone density. Infant receives calcium through breast milk. Recommended 1000mg/day for lactating women.
Top Drug Interactions
| Interacting Drug | Effect | Severity |
|---|---|---|
| Iron supplements | Calcium significantly reduces iron absorption (up to 60%); separate iron and calcium supplements by at least 2 hours; take iron on empty stomach and calcium with food | Moderate |
| Levothyroxine (thyroid hormone) | Calcium carbonate significantly reduces levothyroxine absorption by 20–40%; must separate by ≥4 hours; take levothyroxine first thing in the morning on empty stomach | Major |
| Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) | Calcium chelates fluoroquinolones forming insoluble complexes; significantly reduces antibiotic absorption; separate by ≥2–4 hours | Major |
| Tetracycline / Doxycycline antibiotics | Calcium binds tetracyclines; virtually eliminates antibiotic absorption; NEVER take together; separate by ≥2 hours | Major |
| Bisphosphonates (alendronate, risedronate) | Calcium reduces bisphosphonate absorption; take bisphosphonate first thing in the morning 30–60 min before calcium and any other food/drink | Moderate |
| Vitamin D3 | Beneficial synergistic interaction — vitamin D is required for intestinal calcium absorption; always supplement together for bone health; risk of hypercalcemia only with excessive doses | Minor |
| Thiazide diuretics | Thiazides reduce renal calcium excretion; combined with calcium supplements, risk of hypercalcemia (milk-alkali syndrome if combined with antacid-dose calcium carbonate) | Moderate |
| Digoxin | Hypercalcemia from excessive calcium potentiates digoxin toxicity; monitor serum calcium | Moderate |
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Side Effects
Common
- Constipation (most common; calcium carbonate more constipating than calcium citrate)
- Bloating / Flatulence
- Nausea
- Metallic / Chalky taste
- Belching (antacid use)
Serious / Discontinue If
- Hypercalcemia — headache, nausea, vomiting, confusion, polyuria, muscle weakness; can cause arrhythmias
- Hypercalciuria — renal stones (kidney stones); especially in those with history of kidney stones or high-sodium diets
- Milk-alkali syndrome (rare; from very high-dose calcium carbonate antacid use) — hypercalcemia + metabolic alkalosis + renal insufficiency
- Vascular calcification (chronic excess calcium in CKD / dialysis patients)
- Drug interactions causing therapeutic failure of antibiotics, thyroid medication, bisphosphonates (timing issues)
Contraindications
- Hypercalcemia (any cause)
- Hypercalciuria
- History of calcium-containing renal stones (relative; use with caution + high fluid intake)
- Severe renal impairment without close monitoring
- Milk-alkali syndrome
Available Indian Brands
| Brand | Manufacturer | Price (approx) |
|---|---|---|
| Shelcal 500 | Elder Pharmaceuticals / Torrent | 15 tab ₹88 |
| Calcimax | IPCA Laboratories | 30 tab ₹95 |
| Calcium Sandoz | Novartis India | 30 tab ₹210 |
| Ossopan | Abbott India | 20 tab ₹180 |
| Gemcal | Obstetric & Gynaecology Pharmaceuticals | 15 cap ₹75 |
| Caldikind | Mankind Pharma | 30 tab ₹85 |
| Calcimax Forte | IPCA Laboratories | 30 tab ₹135 |
Monitoring Required
- Serum calcium (before starting; at 4–8 weeks; then every 6 months)
- Serum phosphate (in CKD)
- Urine calcium/creatinine ratio (if renal stone risk or hypercalciuria suspected)
- Renal function (serum creatinine, eGFR)
- Serum PTH (in osteoporosis or CKD management)
- DXA scan (bone mineral density; in osteoporosis management at 1–2 year intervals)
Patient Counseling Points
- Take calcium carbonate WITH meals — it requires stomach acid for absorption (calcium citrate can be taken without food)
- CRITICAL: Separate calcium from iron supplements by at least 2 hours — they compete for absorption
- CRITICAL: Take thyroid medicine (levothyroxine/Eltroxin) at least 4 hours before or after calcium
- CRITICAL: Separate from antibiotics (ciprofloxacin, doxycycline) by at least 2 hours — calcium blocks antibiotic absorption
- Constipation is common with calcium carbonate — increase water and fibre intake; calcium citrate is less constipating if this is a problem
- Vitamin D is required for calcium to work properly — ensure adequate sun exposure or vitamin D supplementation
- Do not exceed the recommended dose — too much calcium can cause kidney stones
- Drink at least 8 glasses of water daily when taking calcium supplements
- Split the dose (e.g., 500mg twice daily) rather than taking all at once — absorption is limited to ~500mg per dose
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Clinically reviewed by: Dr. Amrita Singh, MD (Medicine), DM (Endocrinology), AIIMS New Delhi
Last reviewed: 2026-04-08
References
- ICMR — RDA for Calcium in India 2020
- Indian Osteoporosis Foundation Guidelines 2023
- WHO — Calcium supplementation in pregnant women 2013
- BNF 85 — Calcium carbonate
- UpToDate — Calcium and vitamin D supplementation in osteoporosis
- KDIGO — CKD-MBD Guidelines 2017 Update