Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Antacid.
DEFINITION
Magaldrate Oral Suspension contains Magaldrate in a suitable flavoured vehicle.
The oral suspension complies with the requirements stated under Oral Liquids and with the following requirements.
Content of anhydrous magaldrate, Al5Mg10(OH)31(SO4)2
90.0 to 110.0% of the stated amount.
IDENTIFICATION
A. Dissolve a quantity of the oral suspension containing the equivalent of 0.8 g of anhydrous magaldrate in 20 mL of 3M hydrochloric acid, add 30 mL of water and heat to boiling. Add 6M ammonia until a pH of 6.2 is obtained, continue boiling for a further 2 minutes, filter and retain the precipitate and the filtrate. To 2 mL of the filtrate add 2 mL of ammonium chloride solution and neutralise with a solution prepared by dissolving 2 g of ammonium carbonate and 2 mL of 6M ammonia in sufficient water to produce 20 mL; no precipitate is produced. Add disodium hydrogen phosphate solution; a white, crystalline precipitate is produced which is insoluble in 6M ammonia.
B. The precipitate retained in test A yields the reaction characteristic of aluminium salts, Appendix VI.
C. The filtrate obtained in test A yields the reactions characteristic of sulfates, Appendix VI.
TESTS
Neutralising capacity
Disperse a quantity containing the equivalent of 0.8 g of anhydrous magaldrate in 70 mL of water, heat to 37° and mix for 1 minute. Maintain the temperature at 37° and, while stirring continuously, add from a pipette 30 mL of 1M hydrochloric acid VS. Stir for 15 minutes and, over a period not exceeding 5 minutes, titrate the excess acid with 1M sodium hydroxide VS to a pH of 3.5 which is stable for a period of 10 to 15 seconds. Not more than 12 mL of 1M sodium hydroxide VS is required.
Magnesium hydroxide
Not less than 49.2% and not more than 66.6% of the content of anhydrous magaldrate when determined by the following method. Mix a quantity of the oral suspension containing the equivalent of 1 g of magaldrate in 30 mL of 2M hydrochloric acid and add sufficient water to produce 100 mL (solution A). Dilute 10 mL of this solution to 200 mL with water. Add, while stirring, 1 g of ammonium chloride, 20 mL of triethanolamine, 10 mL of ammonia buffer pH 10.9 and 0.4 mL of mordant black 11 solution. Titrate with 0.05M disodium edetate VS until a blue colour is obtained. Repeat the procedure without the substance being examined. The difference between the titrations represents the amount of disodium edetate required. Each mL of 0.05M disodium edetate VS is equivalent to 2.916 g of Mg(OH)2.
Aluminium hydroxide
Not less than 32.1% and not more than 45.9% of the stated content of anhydrous magaldrate when determined by the following method. Dilute 10 mL of solution A obtained in the test for Magnesium hydroxide with 20 mL of water. Add 25 mL of 0.05M disodium edetate VS, mix, allow to stand for 5 minutes and add 20 mL of acetate buffer pH 4.4, 60 mL of ethanol (96%) and 2 mL of a 0.026% w/v solution of dithizone in ethanol (96%). Titrate with 0.05M zinc sulfate VS until a bright pink colour is obtained. Repeat the procedure without the substance being examined. The difference between the titrations represents the amount of disodium edetate required. Each mL of 0.05M disodium edetate VS is equivalent to 3.90 g of Al(OH)3.
Microbial contamination
Carry out a quantitative evaluation for Enterobacteria and certain other Gram-negative bacteria, Appendix XVI B1. 0.01 mL of the preparation gives a negative result, Table 1 (most probable number of bacteria per gram fewer than 102).
ASSAY
To a quantity of the oral suspension containing the equivalent of 3 g of anhydrous magaldrate add 100 mL of 1M hydrochloric acid VS and mix using a magnetic stirrer to achieve dissolution. Titrate the excess acid with 1M sodium hydroxide VS to pH 3, determined potentiometrically. Repeat the procedure without the preparation being examined. The difference between the titrations represents the amount of hydrochloric acid required. Each mL of 1M hydrochloric acid VS is equivalent to 35.40 mg of Al5Mg10(OH)31(SO4)2.
LABELLING
The quantity of the active ingredient is stated in terms of the equivalent amount of anhydrous magaldrate.
