A-Cal250 mg

A-Cal is used for the following indications, classified by strength of evidence:

Established / FDA-approved uses

• Prevention and treatment of calcium deficiency (dietary supplementation) when dietary calcium intake is inadequate.
• Relief of symptoms of acid indigestion, heartburn, and upset stomach, when used as an antacid at antacid-labeled doses.

Guideline-supported uses

• Adjunctive therapy in the prevention and management of osteoporosis, used together with adequate vitamin D intake and, where indicated, prescription osteoporosis medications, consistent with guidance from bodies such as the National Osteoporosis Foundation.
• Management of hyperphosphatemia in patients with chronic kidney disease, where A-Cal is used as a phosphate binder under medical supervision.

Adjunct / combination-therapy uses

• As a calcium source in combination with vitamin D3 for bone-health support, particularly in postmenopausal women and older adults.

A-Cal is not an antibiotic and has no role in treating infections.

Formulations of Calcium Carbonate are commonly available in strengths such as 500 mg, 600 mg, 750 mg, and 1,250 mg of Calcium Carbonate, corresponding to roughly 200-500 mg of elemental calcium depending on strength. Calcium Carbonate is also formulated in combination with vitamin D3 and other minerals in some products. Exact strength and excipients vary by manufacturer and brand.

A-Cal is an inorganic calcium salt widely used as a dietary calcium supplement and as an antacid. A-Cal (CaCO3) is one of the most concentrated sources of elemental calcium, providing approximately 40% elemental calcium by weight, which makes it a common first-line calcium supplement. A-Cal is available over-the-counter in tablet, chewable tablet, and oral suspension forms, alone or combined with vitamin D3.

A-Cal belongs to the therapeutic classes of Antacids and Calcium Supplements/Minerals. In certain clinical settings, A-Cal is also used as a phosphate binder.

Calcium Carbonate provides elemental calcium, an essential mineral required for bone mineralization, neuromuscular function, cardiac conduction, blood coagulation, and cell signaling. When ingested, Calcium Carbonate reacts with gastric hydrochloric acid to form soluble calcium chloride, which is absorbed in the small intestine, a process enhanced by vitamin D and an acidic gastric environment, and reduced in patients with achlorhydria or those taking acid-suppressing medications.

At antacid doses, Calcium Carbonate acts locally in the stomach, neutralizing gastric acid and raising gastric pH to relieve heartburn and acid indigestion within minutes. As a phosphate binder, Calcium Carbonate binds dietary phosphate in the gut to form insoluble calcium phosphate, which is excreted in the stool, thereby lowering serum phosphate levels.

Chewable tablets of A-Cal should be chewed thoroughly before swallowing. Non-chewable tablets of A-Cal should be swallowed whole with a full glass of water. For optimal absorption, A-Cal should be taken with food, since it requires gastric acid for dissolution. If more than 500 mg of elemental calcium is needed per day, doses of A-Cal should be divided and spaced through the day rather than taken all at once. A-Cal should be separated by at least 2-4 hours from certain other medications (see Interactions).

A-Cal can reduce the absorption of several other medications by forming insoluble complexes or by altering gastric pH. Clinically significant interactions include:

• Tetracycline and fluoroquinolone antibiotics: A-Cal chelates these antibiotics, substantially reducing their absorption and efficacy; separate administration by at least 2-4 hours.
• Bisphosphonates (e.g., alendronate): A-Cal markedly reduces bisphosphonate absorption; take the bisphosphonate at least 30-60 minutes before A-Cal or any other calcium-containing product.
• Levothyroxine: A-Cal reduces levothyroxine absorption; separate dosing by at least 4 hours.
• Thiazide diuretics: concurrent use with A-Cal increases the risk of hypercalcemia due to reduced renal calcium excretion; monitor serum calcium with prolonged concurrent use.
• Digoxin: hypercalcemia resulting from excessive use of A-Cal may increase the risk of digoxin toxicity and cardiac arrhythmia.

Because A-Cal raises gastric pH, it may also reduce absorption of iron salts and certain antifungal or antiviral drugs that require an acidic environment for dissolution; spacing doses from A-Cal is advised.

Common side effects of A-Cal include:

• Constipation
• Gas, bloating, and belching
• Upset stomach or mild nausea

Less common but more serious effects, generally associated with excessive or prolonged high-dose use of A-Cal, include hypercalcemia (fatigue, confusion, muscle weakness, increased thirst/urination), milk-alkali syndrome, and kidney stones. Rebound acid hypersecretion may occur with long-term antacid use of A-Cal. Seek medical attention if severe or persistent symptoms occur.

A-Cal supplementation at recommended dietary allowance doses is commonly used and generally considered beneficial during pregnancy and lactation to support maternal bone health and fetal/infant development, when dietary calcium intake alone is insufficient. However, A-Cal should be used only as directed, and total calcium intake from diet plus supplements should not exceed recommended upper limits, as excessive intake may pose risks. Pregnant and breastfeeding women should consult a physician before starting or adjusting A-Cal supplementation, particularly at doses above typical dietary supplementation levels.

A-Cal requires gastric acid for optimal absorption and should generally be taken with food. Prolonged use of high doses of A-Cal, especially in combination with vitamin D or thiazide diuretics, or in patients with renal impairment, may lead to hypercalcemia or milk-alkali syndrome (hypercalcemia, metabolic alkalosis, and renal insufficiency) — see Contraindications for absolute limits. Patients with a history of kidney stones should use A-Cal only under medical supervision. A-Cal can interfere with absorption of certain other medications (see Interactions); dosing should be separated accordingly. Total daily elemental calcium intake from all sources, including A-Cal, diet, and other supplements, should not exceed recommended upper limits. A-Cal is not an antibiotic and carries no antimicrobial stewardship requirements.

Overdose of A-Cal can cause hypercalcemia, with symptoms such as nausea, vomiting, constipation, confusion, muscle weakness, excessive thirst, frequent urination, and, in severe cases, cardiac arrhythmias, kidney impairment, or milk-alkali syndrome. If overdose of A-Cal is suspected, seek immediate medical attention or contact a poison control center; do not attempt to manage a suspected overdose at home without professional guidance.

Store A-Cal at room temperature (below 30°C), away from light and moisture. Keep out of reach of children.

Pediatric Use

A-Cal may be used in children for calcium supplementation when dietary intake is inadequate, with dosing individualized by age and weight according to recommended dietary allowances; consult a pediatrician before use, especially for indications beyond basic dietary supplementation.

Geriatric Use

Elderly patients may have reduced gastric acid production (achlorhydria), which can reduce absorption of A-Cal; taking it with food helps maintain effectiveness. Elderly patients are also at increased risk of hypercalcemia and renal impairment, warranting monitoring with prolonged use of A-Cal.

Renal Impairment

Use of A-Cal for general supplementation is contraindicated in severe renal impairment (see Contraindications). In chronic kidney disease, A-Cal may be used specifically as a phosphate binder only under nephrology supervision, with regular monitoring of serum calcium and phosphate.

Hepatic Impairment

No specific dose adjustment of A-Cal is established for hepatic impairment, as calcium metabolism is not primarily hepatic; use with routine precautions.

Duration of A-Cal use varies by indication: antacid use is intended for short-term, as-needed symptom relief (if symptoms persist beyond 2 weeks, medical evaluation is advised), whereas calcium supplementation for deficiency prevention or osteoporosis management with A-Cal is typically long-term and ongoing, guided by periodic reassessment of calcium intake and, where relevant, bone density and serum calcium levels by a physician.

Calcium Carbonate is classified under: Antacids; Calcium Supplements (Minerals/Electrolytes); and, in specific clinical contexts, Phosphate Binders.

Calcium Carbonate acts through two principal mechanisms depending on use: as a calcium supplement, Calcium Carbonate dissociates in gastric acid to release calcium ions that are absorbed in the intestine to support bone mineralization, muscle contraction, nerve transmission, and blood clotting; as an antacid, Calcium Carbonate directly neutralizes hydrochloric acid in the stomach, forming calcium chloride, water, and carbon dioxide, thereby raising gastric pH and relieving acid-related symptoms.

A-Cal is used in pediatric patients for prevention and treatment of dietary calcium deficiency, with dosing individualized by age and weight according to recommended dietary allowances for calcium. Safety and efficacy of A-Cal for indications beyond basic dietary calcium supplementation, such as use as a phosphate binder, have not been well established in children, and such use should occur only under specialist supervision. Chewable formulations of A-Cal should be used with caution in young children due to choking risk, and should be kept out of reach of children given the risk of accidental overdose.