Alumina and Magnesium Trisilicate Tablets
»Alumina and Magnesium Trisilicate Tablets contain not less than 90.0percent and not more than 110.0percent of the labeled amounts of aluminum hydroxide [Al(OH)3]and magnesium trisilicate (Mg2Si3O8).
Packaging and storage— Preserve in well-closed containers.
Labeling— Tablets prepared with the use of Dried Aluminum Hydroxide Gelmay be labeled to state the aluminum hydroxide content in terms of the equivalent amount of dried aluminum hydroxide gel,on the basis that each mg of dried gel is equivalent to 0.765mg of 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.
Identification— One powdered Tablet responds to the Identificationtests under Alumina and Magnesium Trisilicate Oral Suspension.
Disintegration á701ñ: 10minutes,simulated gastric fluid TSbeing substituted for water in the test.[NOTE—Tablets that must be chewed before swallowing are exempt from this requirement.]
Uniformity of dosage units á905ñ: meet the requirements for Weight Variationwith respect to aluminum hydroxide and to magnesium trisilicate.
Acid-neutralizing capacity á301ñ— Not less than 5mEq 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 reflux are exempt from this requirement.]
Foam [where Tablets are labeled for the temporary relief of heartburn (acid indigestion)due to acid reflux]— Finely powder a number of Tablets,accurately counted,equivalent to the minimum single dose recommended in the labeling,and transfer the powder to a 100-mLbeaker having an inside diameter of 45mm.Add 5mLof alcohol and sufficient water to make 40mL.Mix at 300rpm for 60seconds,using a magnetic stirrer and a 9.5-×38-mm polytef-coated stirring bar.Stop the stirrer,and carefully add 10mLof 0.5Nhydrochloric acid down the side of the beaker.Stir for 30seconds at 300rpm.Allow to stand for 10minutes,and measure the thickness of the foam layer above the liquid in the beaker:the thickness of the foam is not less than 10mm.
pHá791ñ[where Tablets are labeled for the temporary relief of heartburn (acid indigestion)due to acid reflux]: not less than 4.5,determined on the foam layer obtained in the Foamtest.[NOTE—Take care that the electrodes do not touch the liquid beneath the foam.]
Assay for aluminum hydroxide—
Edetate disodium titrant— Prepare and standardize as directed in the Assayunder Ammonium Alum.
Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 600mg of aluminum hydroxide,to a beaker,add 20mLof water,stir,and slowly add 40mLof 3Nhydrochloric acid.Heat gently,if necessary,to aid solution,cool,and transfer to a 200-mLvolumetric flask.Wash the beaker with water,adding the washings to the flask,add water to volume,and mix.
Procedure— Pipet 10mLof Assay preparationinto a 250-mLbeaker,add 20mLof water,then add,in the order named and with continuous stirring,25.0mLof 0.05MEdetate disodium titrantand 20mLof acetic acid-ammonium acetate buffer TS,and heat the solution near the boiling temperature for 5minutes.Cool,add 50mLof alcohol and 2mLof dithizone TS,and mix.Titrate with 0.05Mzinc sulfate VSuntil the color changes from green-violet to rose-pink.Perform a blank determination,substituting 10mLof water for the Assay preparation,and make any necessary correction.Each mLof 0.05MEdetate disodium titrantconsumed is equivalent to 3.900mg of Al(OH)3.
Assay for magnesium trisilicate—
Potassium chloride solution— Prepare a solution in water containing 5g of potassium chloride per 100mL.
Magnesium standard solution— Transfer 1.000g of magnesium metal to a 1000-mLvolumetric flask containing 50mLof water,and slowly add 10mLof hydrochloric acid.Dilute with water to volume,and mix.Transfer 5.0mLof this solution to a 500-mLvolumetric flask,dilute with water to volume,and mix.
Standard preparations— Transfer 16.0mL,18.0mL,and 20.0mLof Magnesium standard solutionto separate 100-mLvolumetric flasks,add 2.0mLof Potassium chloride solutionto each flask,dilute with water to volume,and mix.These Standard preparationscontain 1.6,1.8,and 2.0µg of magnesium per mL,respectively.[NOTE—Prepare these solutions on the day of use.]
Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 5mg of magnesium trisilicate,to a 100-mLvolumetric flask,and add 10mLof 18Nsulfuric acid.Heat on a steam bath for 30minutes with occasional swirling.Allow to cool,dilute with water to volume,and mix.Filter this solution,discarding the first 20mLof the filtrate.Transfer 20.0mLof the filtrate to a second 100-mLvolumetric flask,add 2.0mLof Potassium chloride solution,dilute with water to volume,and mix.
Procedure— Concomitantly determine the absorbance of the Standard preparationsand the Assay preparationat the magnesium emission line at 285.2nm,with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ),equipped with a magnesium hollow-cathode lamp and a nitrous oxide–acetylene flame,using water as the blank.Plot the absorbances of the Standard preparations,in µg per mL,of magnesium,and draw the line best fitting the three plotted points.From the graph so obtained determine the concentration,C,in µg per mL,of magnesium in the Assay preparation.Calculate the quantity,in mg,of magnesium trisilicate (Mg2Si3O8)in the portion of Tablets taken by the formula:
0.5C(260.86/48.62),
in which 260.86is the molecular weight of anhydrous magnesium trisilicate and 48.62is twice the atomic weight of magnesium.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 86
Phone Number:1-301-816-8251