Magnesia 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

Magnesia Tablets contain NLT 93.0% and NMT 107.0% of the labeled amount of magnesium hydroxide [Mg(OH)₂].

2 IDENTIFICATION

A. Identification Tests—General 〈191〉, Chemical Identification Tests, Magnesium

Sample solution: Crush several Tablets, and dissolve 1 g of the powder in 20 mL of 3 N hydrochloric acid.

Acceptance criteria: Meet the requirements

Delete the following:

B. The retention time of the magnesium peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay. (RB 1-Dec-2022)

3 ASSAY

Change to read:

 Procedure

Sample: A portion of finely powdered Tablets (NLT 20), equivalent to about 250 mg of magnesium hydroxide.

Titrimetric system

Mode: Direct titration

Titrant: 0.05 M edetate disodium VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a 100-mL volumetric flask. Dissolve in 10 mL of 3 N hydrochloric acid, and dilute with water to volume. Filter, if necessary, and transfer 25.0 mL of the filtrate to a beaker containing 75 mL of water. Adjust the reaction of the solution to a pH of 7 (using pH indicator paper; see Reagents, Indicators, and Solutions—Indicator and Test Papers) with 1 N sodium hydroxide, and add 5 mL of ammonia–ammonium chloride buffer TS and 0.15 mL of eriochrome black TS. Titrate with the Titrant to a blue endpoint. Each milliliter of the Titrant is equivalent to 2.916 mg of magnesium hydroxide [Mg(OH)₂]. (RB 1-Dec-2022)

Acceptance criteria: 93.0%–107.0%

4 PERFORMANCE TESTS

Disintegration 〈701〉

Time: NMT 10 min

Analysis: Proceed as directed in the chapter, except substitute simulated gastric fluid TS instead of water.

Acceptance criteria: Meet the requirements

Uniformity of Dosage Units 〈905〉: Meet the requirements

5 SPECIFIC TESTS

Acid-Neutralizing Capacity 〈301〉

Analysis: Proceed as directed in the chapter.

Acceptance criteria: NLT 5 mEq of acid is consumed by the minimum single dose recommended in the labeling, and NLT the number of mEq calculated as follows:

Result = 0.8 × (F_M × M)

F_M = theoretical acid-neutralizing capacity of magnesium hydroxide [Mg(OH)₂], 0.0343 mEq/mg

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

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

Delete the following:

USP Reference Standards 〈11〉

USP Calcium Carbonate RS

USP Magnesium Hydroxide RS (RB 1-Dec-2022)