Magnesium Carbonate, Citric Acid, and Potassium Citrate for Oral Solution

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

Magnesium Carbonate, Citric Acid, and Potassium Citrate for Oral Solution contains a dry mixture of Magnesium Carbonate, Citric Acid, and Potassium Citrate that when constituted as directed in the labeling yields a solution that contains NLT 90.0% and NMT 110.0% of the labeled amount of magnesium citrate (C₁₂H₁₀Mg₃O₁₄).

2 IDENTIFICATION

A. Identification Tests—General, Magnesium 〈191〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: Meets the requirements

B. The retention time of the citrate peak of the Sample solution corresponds to that of Standard solution 1, as obtained in the test for Content of Anhydrous Citric Acid.

3 ASSAY

Procedure

Sample solution: Transfer a volume of constituted oral solution, equivalent to 1.9 g of magnesium citrate to a 100-mL volumetric flask and dilute with water to volume.

Analysis: Transfer 10.0 mL of the Sample solution to a beaker. While stirring, 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 until the last hint of violet disappears (blue endpoint). Each mL of 0.05 M edetate disodium is equivalent to 7.520 mg of magnesium citrate (C₁₂H₁₀Mg₃O₁₄).

Acceptance criteria: 90.0%–110.0%

4 OTHER COMPONENTS

Content of Anhydrous Citric Acid

Mobile phase, Chromatographic system, and System suitability: Proceed as directed in Assay for Citric Acid/Citrate and Phosphate 〈345〉.

Standard solution: 0.02 mg/mL of anhydrous citric acid, from USP Citric Acid RS in a freshly prepared 1 mM sodium hydroxide

Sample solution: Transfer a volume of constituted oral solution equivalent to 500 mg of magnesium citrate, to a suitable volumetric flask, and dilute quantitatively, and stepwise if necessary, with a freshly prepared 1 mM sodium hydroxide to obtain a solution having a concentration of 0.02 mg/mL of magnesium citrate, based on the label claim. Pass through a filter of 0.5-μm or finer pore size, and use the filtrate.

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of anhydrous citric acid (C₆H₈O₇) in relation to the labeled amount of magnesium citrate in the volume of constituted oral solution taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak area of citrate from the Sample solution

r_S = peak area of citrate from the Standard solution

C_S = concentration of citrate in the Standard solution (mg/mL)

C_U = nominal concentration of magnesium citrate in the Sample solution (mg/mL)

Acceptance criteria: 126.1%–154.4% of the labeled amount of magnesium citrate

5 PERFORMANCE TESTS

Uniformity of Dosage Units 〈905〉: Meets the requirements

6 IMPURITIES

Chloride and Sulfate, Chloride 〈221〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: A 2.0-mL portion of Sample solution shows no more chloride than corresponds to 0.30 mL of 0.020 N hydrochloric acid (NMT 0.01%).

Chloride and Sulfate, Sulfate 〈221〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: A 2.0-mL portion of Sample solution shows no more sulfate than corresponds to 0.30 mL of 0.020 N sulfuric acid (NMT 0.015%).

Tartaric Acid

Sample solution: Constitute as directed in the labeling.

Analysis: To 10 mL of Sample solution in a test tube, add 1 mL of glacial acetic acid and 3 mL of a solution of potassium acetate (1 in 2).

Shake the mixture vigorously, then gently rub the inner wall of the test tube with a glass rod for a few min, and allow to stand for 1 h.

Acceptance criteria: No white, crystalline precipitate soluble in 6 N ammonium hydroxide is formed.

7 SPECIFIC TESTS

Microbial Enumeration Tests 〈61〉 and Tests for Specified Microorganisms 〈62〉: The total aerobic microbial count does not exceed 1000 cfu/g, and the total combined molds and yeasts count does not exceed 100 cfu/g. It meets the requirements of the test for absence of Escherichia coli.

pH 〈791〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: 3.3–4.3

8 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, single-dose containers. Store at controlled room temperature.

Labeling: The label specifies the directions for the constitution of the powder and states the equivalent amount of magnesium citrate (C₁₂H₁₀Mg₃O₁₄).