1. Clinical Overview
Calcium (250mg) is an essential mineral supplement, typically administered as calcium carbonate, citrate, or lactate, used to treat and prevent hypocalcemia and associated conditions. It is critical for bone mineralization, neuromuscular function, cardiac conduction, and blood coagulation. In the Indian context, it is widely used for osteoporosis management, pregnancy/lactation support, and as an adjunct in antacid therapy.
| Onset | Duration | Bioavailability |
|---|---|---|
| Absorption begins within 1-2 hours of oral administration, but therapeutic effects on bone mineral density are observed over months. | Serum calcium levels are influenced for 4-6 hours post-dose; skeletal effects are cumulative and long-term. | Approximately 25-35% for calcium carbonate (dose and pH dependent); up to 40% for calcium citrate, especially in achlorhydric patients. Absorption is saturable and inversely related to dose size. |
2. Mechanism of Action
Calcium is the primary mineral component of hydroxyapatite crystals, providing rigidity and strength to bones and teeth. Ionized calcium (Ca2+) in extracellular fluid is crucial for: 1) Stabilizing neuronal membranes and regulating neurotransmitter release. 2) Acting as an intracellular messenger for muscle contraction (via interaction with troponin C). 3) Serving as a cofactor for enzymes in the coagulation cascade (Factors IV, VII, IX, X). 4) Maintaining cardiac muscle contractility and automaticity. Supplementation corrects deficits, suppresses PTH secretion (secondary hyperparathyroidism), and reduces bone resorption.
3. Indications & Uses
- Prevention and treatment of calcium deficiency (Hypocalcemia)
- Prophylaxis and adjuvant therapy for Osteoporosis (postmenopausal, senile, steroid-induced)
- Nutritional supplement in pregnancy and lactation
- As an adjunct in the management of Rickets and Osteomalacia
4. Dosage & Administration
Adult Dosage: Prophylaxis: 250mg to 500mg elemental calcium 2-3 times daily. Treatment of Deficiency: 1-2g elemental calcium per day in divided doses (e.g., 250mg 4 times daily). Maximum daily intake from all sources should not exceed 2500mg.
Administration: Take with or immediately after a meal to enhance absorption and reduce gastric irritation. Calcium carbonate requires stomach acid; take with food. Calcium citrate can be taken without food. Swallow whole with a full glass of water. Do not take within 2 hours of iron supplements, tetracyclines, fluoroquinolones, levothyroxine, or bisphosphonates.
5. Side Effects
Common side effects may include:
- Constipation
- Abdominal discomfort, bloating
- Flatulence
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Levothyroxine | Calcium binds to levothyroxine in the gut, significantly reducing its absorption. | Major |
| Bisphosphonates (Alendronate, Risedronate) | Calcium (and other divalent cations) impair absorption of bisphosphonates. | Major |
| Fluoroquinolones (Ciprofloxacin, Levofloxacin) | Chelation reduces antibiotic absorption and efficacy. | Major |
| Tetracycline antibiotics | Chelation reduces antibiotic absorption and efficacy. | Major |
| Iron supplements | Mutual inhibition of absorption when taken together. | Moderate |
| Digoxin | Hypercalcemia potentiates digoxin effects, increasing risk of toxicity and arrhythmias. | Major |
| Thiazide diuretics | Reduce renal calcium excretion, increasing risk of hypercalcemia. | Moderate |
| Vitamin D analogues (Calcitriol) | Additive effect, significantly increasing risk of hypercalcemia and hypercalciuria. | Major |
| Corticosteroids | Reduce calcium absorption and increase excretion, potentially reducing efficacy. | Moderate |
7. Patient Counselling
- DO take with food for better absorption (especially calcium carbonate).
- DO drink plenty of fluids throughout the day.
- DO take regular, weight-bearing exercise to support bone health.
- DO ensure adequate Vitamin D intake through diet, sun exposure, or supplements.
- DON'T take more than the recommended dose.
- DON'T take calcium at the same time as iron, thyroid medication, or certain antibiotics. Separate by at least 2-4 hours.
- DON'T take if you have a history of kidney stones without consulting your doctor.
8. Toxicology & Storage
Overdose: Acute: Nausea, vomiting, anorexia, constipation, abdominal pain, polyuria, polydipsia, confusion, lethargy, coma. Chronic (Milk-Alkali Syndrome): Hypercalcemia, metabolic alkalosis, renal insufficiency. Severe: Cardiac arrhythmias, renal failure, metastatic calcification.
Storage: Store in a cool, dry place below 30°C. Protect from light and moisture. Keep the container tightly closed. Keep out of reach of children. Do not use after the expiry date printed on the pack.