Calcium Carbonate and Magnesia Chewable Tablets

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION 

Calcium Carbonate and Magnesia Chewable Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of calcium carbonate (CaCO₃) and NLT 90.0% and NMT 115.0% of the labeled amount of magnesium hydroxide [Mg(OH)₂]

2 IDENTIFICATION 

A. Identification Tests—General, Calcium 〈191〉: The addition of 3 N hydrochloric acid to the Chewable Tablets produces effervescence. The resulting solution, after being boiled to expel carbon dioxide and neutralized with 6 N ammonium hydroxide, meets the requirements of the tests. 

B. Identification Tests—General, Magnesium 〈191〉 

Sample solution: Heat 2 Chewable Tablets in 20 mL of 1 N sulfuric acid. Cool, add 20 mL of alcohol, mix, and allow to stand for 30 min. Filter this solution, and add 2 mL of 1 N hydrochloric acid to the filtrate. 

Acceptance criteria: The solution meets the requirements. 

3 ASSAY 

Calcium Carbonate 

Sample solution: Finely powder NLT 20 Chewable Tablets. Transfer a portion of the powder, equivalent to 400 mg of calcium carbonate, to a beaker with 25 mL of water. Add 40 mL of 1 N hydrochloric acid. Heat on a steam bath for 30 min, allow to cool, and transfer with the aid of water to a 100-mL volumetric flask. Dilute with water to volume, mix, filter, and use the filtrate. [Note—Reserve a portion of it for the test for Magnesium Hydroxide.] 

Analysis: Transfer 20.0 mL of the Sample solution to a suitable container, dilute with water to 100 mL, and add 30 mL of 1 N sodium hydroxide, 5 mL of triethanolamine, and 100 mg of hydroxy naphthol blue. Titrate with 0.05 M edetate disodium VS until the solution is deep blue in color. Each mL of 0.05 M edetate disodium is equivalent to 5.004 mg of CaCO₃. 

Acceptance criteria: 90.0%–110.0% 

Magnesium Hydroxide 

Sample solution: Use the Sample solution from the test for Calcium Carbonate. 

Analysis: Transfer a portion of the Sample solution, equivalent to 120 mg of calcium carbonate and magnesium hydroxide combined, to a suitable container. Dilute with water to 100 mL, and add 10 mL of ammonia–ammonium chloride buffer TS, 5 mL of triethanolamine, and 0.3 mL of eriochrome black TS. Titrate with 0.05 M edetate disodium VS to a blue endpoint. The volume, in mL, of 0.05 M edetate disodium consumed, less the volume of 0.05 M edetate disodium corresponding to the content of calcium carbonate in the volume, in mL, of the Sample solution taken, represents the volume, in mL, of 0.05 M edetate disodium equivalent to the quantity of magnesium hydroxide present. Each mL of 0.05 M edetate disodium is equivalent to 2.916 mg of Mg(OH)₂ 

Acceptance criteria: 90.0%–115.0% 

4 PERFORMANCE TESTS 

Uniformity of Dosage Units 〈905〉: Meet the requirements for Weight Variation with respect to calcium carbonate and to magnesia 

5 SPECIFIC TESTS 

Acid-Neutralizing Capacity 〈301〉 

Analysis: NLT 5 mEq of acid is consumed by the minimum single dose recommended in the labeling, and NLT the number of mEq calculated by the formula: 

Result = [0.8 × (F_M × M)] + [0.9 × (F_C × C)]  

F_M = theoretical acid-neutralizing capacity of Mg(OH)₂ , 0.0343 mEq 

M = quantity of Mg(OH)₂ in the sample tested (mg), based on the labeled quantity 

F_C = theoretical acid-neutralizing capacities of CaCO₃, 0.02 mEq 

C = quantity of CaCO₃ in the sample tested (mg), based on the labeled quantity 

6  ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in well-closed containers. 

Labeling: Label the Chewable Tablets to indicate that they must be chewed before being swallowed.