Calcium Carbonate Oral Suspension

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 Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of calcium carbonate (CaCO3).

2 IDENTIFICATION 

A. Identification Tests—General, Calcium〈191〉: The addition of acetic acid to it produces effervescence (presence of carbonate). The resulting solution, after boiling, meets the requirements. 

3 ASSAY 

Procedure 

Sample solution: Transfer a portion of Oral Suspension, equivalent to 1 g of calcium carbonate, previously well shaken in its original container, to a beaker with the aid of 25 mL of water. Add 20 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, and filter. 

Blank: 100 mL of water, 15 mL of 1 N sodium hydroxide, and 5 mL of triethanolamine 

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration 

Titrant: 0.05 M edetate disodium VS 

Indicator: 100 mg of hydroxy naphthol blue 

Endpoint detection: Visual, change to distinct blue 

Analysis: Transfer 20.0 mL of the Sample solution to a suitable container. Dilute with water to 100 mL. Add 15 mL of 1 N sodium hydroxide, 5 mL of triethanolamine, and 100 mg of hydroxy naphthol blue. Titrate with the Titrant. 

Calculate the percentage of the labeled amount of calcium carbonate (CaCO3) in the sample taken: 

Result = [(V_S − V_B) × M × F × 100]/W 

V_S = volume of the Titrant consumed by the Sample solution (mL)  

V_B = volume of the Titrant consumed by the Blank (mL) 

M = Titrant molarity (mmol/mL) 

F = equivalency factor, 100.09 mg/mmol 

W = nominal amount of calcium carbonate taken for the Analysis (mg) 

Acceptance criteria: 90.0%–110.0% 

4 IMPURITIES 

Limit of Fluoride 

[Note—Prepare and store all solutions in plastic containers.] 

Solution A: 294 mg/mL of sodium citrate dihydrate in water 

Standard stock solution: 1.1 mg/mL of USP Sodium Fluoride RS in water 

Standard solution: Combine 20.0 mL of the Standard stock solution with 50.0 mL of Solution A, and dilute with water to 100.0 mL. [Note—Each mL of this solution contains 100 µg of fluoride ion.] 

Sample solution: Transfer a portion of Oral Suspension, equivalent to 2.0 g of calcium carbonate, to a beaker containing a plastic-coated stirring bar. Add 20 mL of water and 4.0 mL of hydrochloric acid. Stir until dissolved. Add 50.0 mL of Solution A and sufficient water to make 100.0 mL. 

Electrode system: Use a fluoride-specic ion-indicating electrode and a silver–silver chloride reference electrode connected to a pH meter capable of measuring potentials with a minimum reproducibility of ±0.2 mV (see pH 〈791〉). 

Standard response line: Transfer 50.0 mL of Solution A and 4.0 mL of hydrochloric acid to a beaker. Add water to make 100.0 mL. Add a plastic-coated stirring bar, insert the electrodes into the solution, and stir for 15 min. Read the potential, in mV. Continue stirring, and at 5- min intervals add 100, 100, 300, and 500 µL of the Standard solution, reading the potential 5 min after each addition. Plot the logarithms of the cumulative fluoride ion concentrations (0.1, 0.2, 0.5, and 1.0 µg/mL) versus potential, in mV. 

Analysis: Rinse and dry the electrodes, and insert them into the Sample solution. Stir for 5 min, and read the potential, in mV. From the measured potential and the Standard response line, determine the concentration, C, in µg/mL, of fluoride ion in the Sample solution. Calculate the content of fluoride in the sample taken: 

Result = (V × C)/W 

V = volume of the Sample solution (mL) 

C = determined concentration of fluoride in the Sample solution (µg/mL) 

W = nominal weight of calcium carbonate taken (g) 

Acceptance criteria: 50 µg/g, with respect to the labeled amount of calcium carbonate 

Change to read: 

Arsenic 〈211〉, Procedures, Procedure 1 

Test preparation: Slowly dissolve a portion of Oral Suspension equivalent to 1.0 g of calcium carbonate in 15 mL of hydrochloric acid. Dilute with water to 55 mL. 

Analysis: Proceed as directed in the chapter, except omit the addition of 20 mL of 7 N sulfuric acid specified under Procedure. Acceptance criteria: NMT 3 µg/g, with respect to the labeled amount of calcium carbonate 

Change to read: 

Lead 〈251〉, Procedures, Procedure 1  

Test preparation: Mix a portion of Oral Suspension equivalent to 1.0 g of calcium carbonate in 5 mL of water. 

Analysis: To the Test preparation slowly add 8 mL of 3 N hydrochloric acid. Evaporate on a steam bath to dryness, and dissolve the residue in 5 mL of water. 

Acceptance criteria: NMT 3 µg/g, with respect to the labeled amount of calcium carbonate 

5 SPECIFIC TESTS 

Microbial Enumeration Tests 〈61〉and Tests for Specified Microorganisms 〈62〉: The total aerobic microbial count is NMT 102 cfu/mL. It meets the requirements of the tests for absence of Escherichia coli and Pseudomonas aeruginosa. 

pH 〈791〉: 7.5–8.7 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers, and avoid freezing. 

USP Reference Standards 〈11〉 

USP Sodium Fluoride RS