Co-magaldrox Tablets

General Notices

Magnesium Hydroxide and Aluminium Hydroxide Tablets

Action and use

Antacid.

Definition

Co-magaldrox Tablets contain Magnesium Hydroxide and Dried Aluminium Hydroxide. The amount of Dried Aluminium Hydroxide is adjusted to give the required content of Al2O3.

The tablets comply with the requirements stated under Tablets and with the following requirements.

Content of magnesium hydroxide, Mg(OH)2

90.0 to 110.0% of the stated amount.

Content of Al2O3

45.0 to 55.0% of the stated amount of dried aluminium hydroxide.

Identification

A. To a quantity of the powdered tablets containing about 0.2 g of magnesium hydroxide in 10 mL of 2m hydrochloric acid add 0.25 mL of methyl red solution and heat to boiling. Add 6m ammonia until the solution becomes yellow, continue boiling for 2 minutes and filter. To 1 mL of the filtrate add 1 mL of 6m ammonia and 1 mL of 2m ammonium chloride; no precipitate is produced. Add 0.25m disodium hydrogen orthophosphate; a white crystalline precipitate is produced which is insoluble in 6m ammonia.
B. Shake a quantity of the powdered tablets containing 0.25 g of dried aluminium hydroxide with 25 mL of 2m hydrochloric acid and filter. The filtrate yields the reaction characteristic of aluminium salts, Appendix VI.

Assay

For Al2O3

Weigh and powder 20 tablets. To a quantity of the powdered tablets containing 1.5 g of dried aluminium hydroxide add 20 mL of water, stir and slowly add 30 mL of 3m hydrochloric acid. Heat gently, if necessary, to aid solution, cool, filter, wash the filter well with water, dilute the combined filtrate and washings to 200 mL with water and mix. Reserve a portion of the solution for the Assay for magnesium hydroxide. To 10 mL add 20 mL of water and, with continuous stirring, 25 mL of 0.05m disodium edetate VS followed by 20 mL of a mixture of equal volumes of 2m ammonium acetate and 2m acetic acid. Heat near the boiling point for 5 minutes, cool, add 50 mL of absolute ethanol and 3 mL of a freshly prepared 0.025% w/v solution of dithizone in absolute ethanol. Titrate the excess of disodium edetate with 0.05m zinc sulfate VS until the colour of the solution changes from greenish blue to reddish violet. Each mL of 0.05m disodium edetate VS is equivalent to 2.549 mg of Al2O3.

For magnesium hydroxide

To a volume of the solution reserved in the Assay for Al2O3 containing about 40 mg of magnesium hydroxide add 200 mL of water and 20 mL of triethanolamine and stir. Add 10 mL of ammonia buffer pH 10.9 and cool the solution to between 3° and 4° by immersion in iced water. Titrate the cooled solution with 0.05m disodium edetate VS using mordant black 11 solution as indicator. Each mL of 0.05m disodium edetate VS is equivalent to 2.916 mg of Mg(OH)2.