ANTACID CALCIUM

General Administration Information
For storage information, see the specific product information within the How Supplied section.

Route-Specific Administration

Oral Administration
-Generally, administer with meals or feedings for improved absorption. Follow each dose with appropriate fluid intake.
-Because calcium carbonate, like other antacids or calcium-containing products, may interfere with the absorption of other medicines, separate administration of calcium carbonate from other medications according to recommendations for the potentially interacting medication.
Oral Solid Formulations
-Chewable tablets: Instruct patient to chew thoroughly before swallowing.

Oral Liquid Formulations
-Oral suspension: Shake well before each administration. Use an oral syringe or other calibrated oral dosing device to measure and administer an accurate dosage.

Common GI adverse reactions associated with calcium carbonate therapy include flatulence, gastric distension, constipation, and eructation.


Large doses of calcium carbonate can lead to the development of hypercalcemia or nephrolithiasis (kidney stones or renal calculi) in susceptible patients. Clinical manifestations of hypercalcemia may include anorexia, thirst, nausea, vomiting, constipation, abdominal pain, muscle weakness (myasthenia), fatigue, mental disturbances, polydipsia, polyuria, bone pain, nephrocalcinosis, renal calculi (nephrolithiasis) and in severe cases, cardiac arrhythmias. Patients with electrolyte imbalances and renal impairment or dehydration are predisposed to developing the milk-alkali syndrome, characterized by hypercalcemia and metabolic alkalosis and, if left untreated, renal failure.

Hypophosphatemia, though rare, can potentially occur in patients during chronic calcium carbonate therapy if dietary phosphate levels are low due to the malabsorption of phosphate from the diet as calcium carbonate binds with phosphate in the gut.

Hypercalcemia from any cause including, but not limited to, hyperparathyroidism, hypercalcemia of malignancy (neoplastic disease), or sarcoidosis would contraindicate therapy with calcium carbonate. Patients with a history of preexisting hypercalcemia, renal disease (renal failure), or dehydration are predisposed to developing milk-alkali syndrome and calcinosis. Symptoms of this syndrome include hypercalcemia, nausea/vomiting, headache, weakness, metabolic alkalosis, and change in mental status. Calcium blood concentrations should be monitored routinely in such patients who are receiving calcium carbonate therapy. If administration of calcium carbonate is needed in patients with a history of nephrolithiasis (kidney stones) or hypercalciuria, urinary calcium excretion and other appropriate testing should be monitored periodically.

The use of calcium carbonate can be constipating and it should be used cautiously in patients with preexisting constipation or with GI bleeding, GI obstruction or ileus, or decreased gastric motility.

In infants at high risk for necrotizing enterocolitis, oral liquid calcium formulations should be avoided due to the high osmolality.

Description: Calcium is the most abundant cation and the fifth most common inorganic element in the human body. Calcium is essential for the maintenance of the nervous, muscular, and skeletal systems, and for cell membrane and capillary permeability. Its role in bone structure and muscle contraction is well known, but calcium is also important for blood coagulation, nerve conduction, and electrical conduction in the myocardium. In general, calcium salts are used to treat or prevent calcium depletion. Calcium carbonate has been used for children with chronic kidney disease to maintain phosphorus concentrations < 5.5 mg/dl; however, calcium acetate may be preferable due to lower incidences of hypercalcemia. Calcium carbonate is also used as an antacid for the temporary relief of heartburn. Neonatal hypocalcemia is fairly common within the first few days of life, particularly in premature infants. Following IV treatment, oral calcium supplements such as calcium carbonate are frequently necessary; however, liquid oral calcium formulations should be avoided in infants at high risk for necrotizing enterocolitis (i.e., premature infants) due to the high osmolality. Calcium carbonate suspension is not labeled for use in children; however, it is widely used in pediatric patients as young as neonates. Some tablet formulations are labeled for use in pediatric patients as young as 2 years of age.

General Information:
-NOTE: other Calcium Salts are discussed in a separate monograph.

Elemental Calcium Content
NOTE: Different calcium formulations are not directly exchangeable on a mg per mg basis; the different salts contain roughly the following amounts of elemental calcium (1 mEq elemental calcium is equivalent to about 20 mg elemental calcium):
Calcium Formulation: (Elemental Calcium content per g)
-Calcium Acetate: 250 mg (12.5 mEq) per g
-Calcium Carbonate: 400 mg (20 mEq) per g
-Calcium Chloride: 270 mg (13.5 mEq) per g
-Calcium Citrate: 210 mg (10.5 mEq) per g
-Calcium Glubionate: 64 mg (3.2 mEq) per g
-Calcium Gluconate: 93 mg (4.65 mEq) per g
-Calcium Lactate: 130 mg (6.5 mEq) per g

For nutritional supplementation to provide the recommended dietary allowance (RDA) in healthy individuals:
Oral dosage:
Premature Neonates: 150 to 220 mg/kg/day PO based on adequate intake (AI). A recommended dietary allowance (RDA) has not been established.
Neonates and Infants < 6 months: 200 mg/day PO based on adequate intake (AI). A recommended dietary allowance (RDA) has not been established.
Infants >= 6 months: 260 mg/day PO based on adequate intake (AI). A recommended dietary allowance (RDA) has not been established.
Children 1-3 years: 700 mg/day PO is the recommended dietary allowance (RDA).
Children 4-8 years: 1,000 mg/day PO is the recommended dietary allowance (RDA).
Children >= 9 years and Adolescents: 1,300 mg/day PO is the recommended dietary allowance (RDA).

For the treatment of hypocalcemia:
NOTE: Base dose on clinical condition and serum calcium concentration. Serum concentrations of ionized calcium may be necessary to guide dosage adjustments in some persons, especially those with hypoalbuminemia.
Oral dosage:
Neonates: 100 to 250 mg/kg/day (40 to 100 mg/kg/day elemental calcium) PO in 4 to 6 divided doses, initially. Titrate dose based on symptom control and target calcium concentrations.
Infants, Children, and Adolescents: 75 to 187.5 mg/kg/day (30 to 75 mg/kg/day elemental calcium) PO in 3 to 4 divided doses, initially. Titrate dose based on symptom control and target calcium concentrations. Doses as high as 250 mg/kg/day (100 mg/kg/day elemental calcium) PO may be necessary. Usual Max: 22,500 mg/day (9,000 mg/day elemental calcium).

For the treatment of hyperphosphatemia associated with chronic kidney disease*:
NOTE: Calcium carbonate has been designated as orphan drug by the FDA for this purpose.
Oral dosage:
Infants, Children, and Adolescents: 1,000 to 1,500 mg PO 3 times daily (1,200 to 1,800 mg elemental calcium/day) with each meal, initially. Titrate dose to target serum phosphorus concentration. Usual Max: 5,000 mg/day (2,000 mg/day of elemental calcium). Calcium carbonate lowers serum phosphate concentrations similarly to calcium acetate; however, calcium carbonate contains more elemental calcium and hypercalcemia has been noted more frequently with calcium carbonate compared with calcium acetate.

For the temporary relief of pyrosis (heartburn) or dyspepsia, or for symptomatic relief of hyperacidity associated with peptic ulcer, gastritis, esophagitis, gastric hyperacidity, or hiatal hernia:
Oral dosage:
Children 2-5 years: 375 to 750 mg (150 to 300 mg of elemental calcium) PO; repeat as needed (Max: 1,200 to 1,500 mg/day; 480 to 600 mg of elemental calcium). Number of tablets varies depending on formulation.
Children 6-11 years: 750 to 800 mg (300 to 320 mg of elemental calcium) PO; repeat as needed (Max: 2,400 to 3,000 mg/day; 960 to 1,200 mg of elemental calcium). Number of tablets varies depending on formulation.
Children and Adolescents >= 12 years: 1,000 to 3,000 mg (400 to 1,200 mg elemental calcium) PO; repeat as needed (Max: 7,000 to 7,500 mg/day; 2,800 to 3,000 mg elemental calcium). Number of tablets varies depending on formulation.

Therapeutic Drug Monitoring:
Ionized calcium concentrations are the preferred measure to determine true hypocalcemia. If total serum calcium concentrations are obtained, calcium concentrations should be adjusted if hypoalbuminemia or hyperalbuminemia is present. The corrected calcium concentration may be estimated from the following formula :
-Corrected calcium (mg/dl) = serum calcium (mg/dl) + 0.8 [4- serum albumin (g/dl)]

Maximum Dosage Limits:
-Neonates
Generally, 250 mg/kg/day (100 mg/kg/day elemental calcium) PO for hypocalcemia; tolerable upper intake level as a nutrient has not been established.
-Infants
Generally, 250 mg/kg/day (100 mg/kg/day elemental calcium) PO for hypocalcemia; tolerable upper intake level as a nutrient has not been established.
-Children
Generally, 250 mg/kg/day (100 mg/kg/day elemental calcium) PO for hypocalcemia; tolerable upper intake level as a nutrient is 6,250 mg/day (2,500 mg/day elemental calcium).
-Adolescents
Generally, 250 mg/kg/day or 22,500 mg/day (100 mg/kg/day or 9,000 mg/day elemental calcium) PO for hypocalcemia; tolerable upper intake level as a nutrient is 6,250 mg/day (2,500 mg/day elemental calcium).

Patients with Hepatic Impairment Dosing
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed. Adjust dosage based on patient response and serum calcium concentrations.

Patients with Renal Impairment Dosing
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed. Adjust dosage based on patient response and serum calcium concentrations.

*non-FDA-approved indication

Monograph content under development

Mechanism of Action: Calcium is the primary component of skeletal tissue, providing structural integrity and support for individual growth. Bone undergoes constant remodeling and turnover. Mineral release during the process of bone resorption buffers hydrogen ions. Whereas, the formation of bone generates hydrogen ions. Thus, bone serves as a calcium depot and as a reservoir for electrolytes and buffers. Inhibition of bone resorption is primarily the function of the hormone, calcitonin. The control of plasma calcium concentration is primarily maintained by parathyroid hormone, thyroxine, and 1,25 dihydroxycholecalciferol. Ionized calcium is the physiologically active form. Basic metabolic functions involve the cardiac, neuromuscular, structural, and blood coagulation systems.

Calcium carbonate also works as a phosphate binder. When taken with meals, it combines with dietary phosphate, forming an insoluble calcium-phosphate complex, which is then eliminated in the feces. This in turn lowers serum phosphorus concentrations.

Pharmacokinetics: Calcium is required by all body tissues. Approximately 98% of the body's calcium is stored in the bone, primarily as the hydroxyapatite. Constant bone remodeling and turnover of the skeleton release calcium into the systemic circulation which is then re-accumulated by the bone on a daily basis. Calcium is 40% bound to plasma proteins, primarily albumin and 10% is in a chelated form. Approximately 50% of serum calcium is ionized, which is considered the physiologically active form. The ultrafiltratable calcium (nonprotein-bound) is distributed to the protein-poor regions of the body, such as the cerebrospinal and extracellular fluids. Calcium is primarily excreted in the feces and bile (80%). Urinary excretion accounts for the remainder (20%). However, approximately 99% of filtered calcium is reabsorbed by the kidney with less than 1% excreted. Parathyroid hormone, calcitonin, and 1,25 dihydroxycholecalciferol are primarily responsible for controlling calcium equilibrium. Insulin, thyroxine, growth hormone, androgens, estrogens, adrenal corticosteroids, and inorganic phosphate also contribute.

Affected cytochrome P450 isoenzymes: none


-Route-Specific Pharmacokinetics
Oral Route
Absorption of calcium is optimal when it is taken in a dose of <= 500 mg.

Calcium carbonate vs. citrate
Bioavailability studies of calcium carbonate compared to calcium citrate have reported variable results. One study reported similar bioavailability between the 2 formulations (approximately 28% for 500-mg dose and 36% for 1000-mg dose). Another study reported better bioavailability with calcium citrate when given with food. Calcium citrate offers better absorption under achlorhydria conditions; therefore, this supplement is recommended in patients receiving proton-pump inhibitors or H2 blockers. Calcium carbonate should be taken with meals for optimal absorption.