Digitoxin Tablets

Action and use

Na /K-ATPase inhibitor; cardiac glycoside.

Definition

Digitoxin Tablets contain Digitoxin.

Content of digitoxin, C₄₁H₆₄O₁₃

90.0 to 110.0% of the stated amount.

Identification

To a quantity of the powdered tablets containing 0.25 mg of Digitoxin add 1 mL of glacial acetic acid containing 0.01% w/v of iron(iii) chloride, shake for a few minutes, filter through sintered glass and cautiously add 1 mL of sulfuric acid to the filtrate without mixing. A brown ring free from red colour is produced at the interface and, after a short time, an indigo colour is produced in the upper layer.

TEST

Uniformity of content

Tablets containing less than 2 mg and/or less than 2% w/w of Digitoxin comply with the requirements stated under Tablets using the following method of analysis. Shake one tablet with 15 mL of methanol (50%) for 30 minutes and dilute to 25 mL with the same solvent. Filter through a suitable membrane filter disc having an average pore diameter not greater than 0.8 µm, discarding the first few mL of the filtrate, and transfer 1 mL to a 10 mL graduated flask. Add 3 mL of a 0.1% w/v solution of l-ascorbic acid in methanol and 0.2 mL of a 0.009m solution of hydrogen peroxide prepared by accurately diluting hydrogen peroxide solution (100 vol) that has been standardised by titration with 0.02m potassium permanganate VS, mix and dilute to volume with hydrochloric acid. After exactly 30 minutes measure the fluorescence of the solution, Appendix II E, using an excitation wavelength of 400 nm and an emission wavelength of 570 nm and setting the instrument to zero with water. Calculate the content of digitoxin, C₄₁H₆₄O₁₃, from the fluorescence obtained by carrying out the operation at the same time using a 0.0004% w/v solution of digitoxin BPCRS in methanol (50%) and beginning at the words ‘transfer 1 mL ...’.

Assay

Weigh and finely powder 20 tablets. To a quantity of the powder containing 1.25 mg of Digitoxin add 3 mL of water, swirl to disperse the powder and allow to stand for 10 minutes, swirling occasionally. Add 25 mL of glacial acetic acid, shake for 1 hour and filter (Whatman No. 1 paper is suitable), discarding the first few mL of filtrate. To 4 mL of the filtrate add 1 mL of dimethyl sulfoxide, dilute to 25 mL with xanthydrol reagent, mix well and allow to stand in the dark for 4.5 hours (solution A). At the same time prepare two further solutions in the same manner but using for solution B 4 mL of digitoxin standard solution and for solution C 4 mL of a mixture of 25 volumes of glacial acetic acid and 3 volumes of water and beginning at the words ‘add 1 mL of dimethyl sulfoxide ...’. Measure the absorbances of solutions A and B at the maximum at 550 nm, Appendix II B, using solution C in the reference cell.