Alumina and Magnesium Trisilicate 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

Alumina and Magnesium Trisilicate Tablets contain NLT 90.0% and NMT 110.0% of the labeled amounts of aluminum hydroxide [Al(OH)₃] and magnesium trisilicate (Mg₂Si₃O₈).

2 IDENTIFICATION

Delete the following:

A. Identification Tests - General 〈191〉, Chemical Identification Tests, Magnesium(USP 1-May-2024)

Add the following:

A. Characteristic emission lines for magnesium at 279 and 285 nm from the Sample solution correspond to those of Standard solution 1, Standard solution 2, or Standard solution 3, as obtained in the Assay. (USP 1-May-2024)

Delete the following:

B. Identification Tests-General 〈191〉, Chemical Identification Tests, Aluminum (USP 1-May-2024)

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B. Characteristic emission lines for aluminum at 308 and 394 nm from the Sample solution correspond to those of Standard solution 1, Standard solution 2, or Standard solution 3, as obtained in the Assay. (USP 1-May-2024)

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C. Silicon Dioxide

Sample: One Tablet

Analysis: Powder the Sample. Mix the powder with 10 mL of 3 N hydrochloric acid. To this mixture add 5 drops of methyl red TS, heat to boiling, add 6 N ammonium hydroxide until the color of the solution changes to deep yellow, then continue boiling for 2 min, and filter. Wash the solids on the filter with 20 mg/mL of hot ammonium chloride solution, add 10 mL of 3 N hydrochloric acid, and filter. Transfer the filter paper and its contents to a small platinum dish and ignite to constant weight (W ). Cool in a desiccator after each ignition. Moisten the residue with water, and add 6 mL of hydrofluoric acid. Evaporate to dryness, ignite for 5 min, cool in a desiccator, and weigh (W ).

[Note - The loss in weight represents the weight of silicon dioxide (SiO₂).]

Calculate the percentage of silicon dioxide (SiO ) that is lost between the initial ignition and the final ignition:

Result = [(W_i− W_f)/W_i] × 100

W_i = weight of the residue from the initial ignition

W_f = weight of the residue from the final ignition (USP 1-May-2024)

Acceptance criteria: NLT 10%

3 ASSAY

Delete the following:

Procedure 1: Aluminum Hydroxide (USP 1-May-2024)

Delete the following:

Procedure 2: Magnesium Trisilicate (USP 1-May-2024)

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3.1 Procedure

Use water with a resistivity of NLT 18 megohm-cm to prepare the solutions.

Diluent: 2% (w/v) nitric acid

Standard stock solution: 500 mg/L of aluminum and 250 mg/L of magnesium in Diluent prepared as follows. Transfer appropriate amounts of USP Aluminum Sulfate RS and USP Magnesium Carbonate RS to a suitable volumetric flask. Dissolve and dilute with Diluent to volume.

Internal standard solution: 100 mg/L of yttrium in Diluent

Blank solution: 2 mg/L of yttrium from the Internal standard solution in Diluent

Standard solution 1: 10 mg/L of aluminum, 5 mg/L of magnesium, and 2 mg/L of yttrium from the Standard stock solution and the Internal standard solution in Diluent

Standard solution 2: 50 mg/L of aluminum, 25 mg/L of magnesium, and 2 mg/L of yttrium from the Standard stock solution and the Internal standard solution in Diluent

Standard solution 3: 75 mg/L of aluminum, 37.5 mg/L of magnesium, and 2 mg/L of yttrium from the Standard stock solution and the Internal standard solution in Diluent

Sample stock solution: Nominally 360 mg/L of aluminum hydroxide from Tablets prepared as follows. Finely powder Tablets (NLT 30).

Transfer a portion of the powder, equivalent to 18 mg of aluminum hydroxide, to a microwave digestion vessel. Add 5 mL each of water and nitric acid, in the order named. Perform the closed-vessel microwave-assisted digestion according to parameters specified in Table 1. Cool down to room temperature, transfer to a 50-mL volumetric flask, wash the vessel with water, adding the washings to the flask, and dilute with Diluent to volume. [Note - A cool down time of 15 min may be suitable after digestion.]

Table 1

Sample solution: Nominally 144 mg/L of aluminum hydroxide and 2 mg/L of yttrium prepared from the Internal standard solution and the Sample stock solution

[Note - Concentrations of aluminum and magnesium in the Sample solution may be modified to fit the linear or working range.]

3.2 Instrumental conditions

Mode: ICP–OES

Analytical wavelengths: Characteristic emission lines for aluminum at 308 nm, magnesium at 279 nm, and yttrium at 371 nm. For Identification A, detect additional magnesium emission line at 285 nm. For Identification B, detect additional aluminum emission line at 394 nm.

3.3 System suitability

Samples: Blank solution, Standard solution 1, Standard solution 2, and Standard solution 3

3.4 Suitability requirements

Correlation coeficient: NLT 0.999 for aluminum and magnesium, from the linear regression in the Analysis

Drift: NMT 5.0% for aluminum and magnesium, compare concentrations determined from Standard solution 2 before and after the analysis of the Sample solution

Relative standard deviation: NMT 2.0% for aluminum and magnesium from five replicate analyses of Standard solution 2

3.5 Analysis

Samples: Blank solution, Standard solution 1, Standard solution 2, Standard solution 3, and Sample solution

Use internal standardization technique to construct linear calibration curves by plotting the intensity of the emission (corrected for any changes in yttrium emission intensity) from Blank solution, Standard solution 1, Standard solution 2, and Standard solution 3 versus their corresponding concentrations, in mg/L, for aluminum and magnesium, respectively. Determine the concentration (C_s), in mg/L, for aluminum and magnesium in the Sample solution using the corresponding linear calibration curve.

Calculate the percentage of the labeled amount of aluminum hydroxide [Al(OH)₃] in the portion of Tablets taken:

Result = (C_s/C_u) × (M_r/A_r) × 100

C_s = concentration of aluminum in the Sample solution determined (mg/L)

C_u = nominal concentration of aluminum hydroxide in the Sample solution (mg/L)

M_r = molecular weight of aluminum hydroxide, 78.00

A_r = atomic weight of aluminum, 26.98

Calculate the percentage of the labeled amount of magnesium trisilicate (Mg Si O ) in the portion of Tablets taken:

Result = (C_s/C_u) × (M_r/A_r) × (1/F) × 100

C_s = concentration of magnesium in the Sample solution determined (mg/L)

C_u = nominal concentration of magnesium trisilicate in the Sample solution (mg/L)

M_r = molecular weight of magnesium trisilicate, 260.86

A_r = atomic weight of magnesium, 24.31

F = number of magnesium in one mole of magnesium trisilicate, 2

Acceptance criteria: 90.0%–110.0% (USP 1-May-2024)

4 PERFORMANCE TESTS

Disintegration 〈701〉

Medium: Simulated gastric fiuid TS

Time: 10 min

Acceptance criteria: Meet the requirements

[Note - Tablets that must be chewed before swallowing are exempt from this requirement.]

Uniformity of Dosage Units 〈905〉, Weight Variation: Meet the requirements with respect to aluminum hydroxide [Al(OH)₃] and to magnesium trisilicate (Mg₂Si₃O₈).

5 SPECIFIC TESTS

5.1 Acid-Neutralizing Capacity 〈301〉

Acceptance criteria: NLT 5 mEq of acid is consumed by the minimum single dose recommended in the labeling.

[Note - Tablets labeled for the temporary relief of heartburn (acid indigestion) due to acid re flux are exempt from this requirement.]

5.2 Foam

[where Tablets are labeled for the temporary relief of heartburn (acid indigestion) due to acid reflux]

Sample solution: Finely powder a number of Tablets, equivalent to the minimum single dose recommended in the labeling, and transfer the powder to a 100-mL beaker having an inside diameter of 45 mm. Add 5 mL of alcohol and sufficient water to make 40 mL.

Analysis: Mix the Sample solution at 300 rpm for 60 s, using a magnetic stirrer and a 9.5-mm × 38-mm polytef-coated stirring bar. Stop the stirrer, and carefully add 10 mL of 0.5 N hydrochloric acid down the side of the beaker. Stir for 30 s at 300 rpm. Allow to stand for 10 min, and measure the thickness of the foam layer above the liquid in the beaker.

Mg₂Si₃O₈NLT 10 mm

5.3 pH 〈791〉

(where Tablets are labeled for the temporary relief of heartburn (acid indigestion) due to acid reflux)

Sample: The foam layer obtained in the Foam test

[Note - Take care that the electrodes do not touch the liquid beneath the foam.]

Acceptance criteria: NLT 4.5

6 ADDITIONAL REQUIREMENTS

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Packaging and Storage: Preserve in well-closed containers. Store at up to 25° in a dry place. (USP 1-May-2024)

Labeling: Tablets prepared with the use of Dried Aluminum Hydroxide Gel may be labeled to state the aluminum hydroxide content in terms of the equivalent amount of dried aluminum hydroxide gel, on the basis that each milligram of dried gel is equivalent to 0.765 mg of aluminum hydroxide [Al(OH)₃]. Tablets intended for the temporary relief of heartburn (acid indigestion) due to acid reflux are so labeled. Tablets that must be chewed before swallowing are so labeled.

Change to read:

USP Reference Standards 〈11〉

USP Aluminum Sulfate RS

USP Magnesium Carbonate RS