Magnesium Carbonate, Citric Acid, and Potassium Citrate for Oral Solution
» 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 not less than 90.0 percent and not more than 110.0 percent of the labeled amount of magnesium citrate (C12H10Mg3O14).
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).
USP Reference standards 11
Microbial enumeration tests 61 and Tests for specified microorganisms 62 The total aerobic microbial count does not exceed 1000 cfu per g, and the total combined molds and yeasts count does not exceed 100 cfu per g. It meets the requirements of the test for absence of Escherichia coli.
Uniformity of dosage units 905: meets the requirements.
pH 791: between 3.3 and 4.3, determined in a solution constituted as directed in the labeling.
Content of anhydrous citric acid
Mobile Phase and Chromatographic System Proceed as directed under Assay for Citric Acid/Citrate and Phosphate 345.
Standard preparation Dissolve USP Citric Acid RS in a freshly prepared 1 mM sodium hydroxide to obtain a solution having a known concentration of about 0.02 mg of anhydrous citric acid per mL.
Assay preparation Constitute the Oral Solution as directed in the labeling. Transfer the amount of the constituted Oral Solution, equivalent to about 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 about 0.02 mg of magnesium citrate per mL, based on the label claim. Pass the resulting solution through a filter having a 0.5-µm or finer porosity, and use the filtrate.
Procedure Proceed as directed for Procedure under Assay for Citric Acid/Citrate and Phosphate 345, and calculate the content, in g, of anhydrous citric acid (C6H8O7) by the formula:
0.001(CS DVT /V)(rU / rS)in which 0.001 is the conversion factor from mg to g; CS is the concentration, in mg per mL, of anhydrous citric acid in the Standard preparation; D is the dilution factor for the Assay preparation; VT is the total volume of constituted Oral Solution, as measured, when constituted as directed; V is the volume, in mL, of the constituted Oral Solution taken to prepare the Assay preparation; and rU and rS are the citrate peak areas obtained from the Assay preparation and the Standard preparation, respectively. The content of anhydrous citric acid is between 126.1% and 154.4% of the labeled amount of magnesium citrate.
Other requirements Constitute as directed in the labeling: it meets the requirements of the tests for Identification, Chloride, Sulfate, and Tartaric acid under Magnesium Citrate Oral Solution.
Assay Transfer an accurately measured volume of the constituted Oral Solution, equivalent to about 0.5 g of magnesium oxide, to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a beaker. While stirring, add 10 mL of ammoniaammonium chloride buffer TS, 5 mL of triethanolamine, 0.3 mL of eriochrome black TS, and 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).
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USP35NF30 Page 3743Pharmacopeial Forum: Volume No. 31(5) Page 1386