Aminophylline Rectal Solution
» Aminophylline Rectal Solution is an aqueous solution of Aminophylline, prepared with the aid of Ethylenediamine. It contains an amount of aminophylline equivalent to not less than 90.0 percent and not more than 110.0 percent of the labeled amount of anhydrous theophylline (C7H8N4O2).
Aminophylline Rectal Solution may contain an excess of ethylenediamine, but no other substance may be added for the purpose of pH adjustment.
Packaging and storage— Preserve in tight, single-dose or multiple-dose containers, at controlled room temperature.
Labeling— Label the Rectal Solution to state the content of anhydrous theophylline.
USP Reference standards 11
USP Theophylline RS Click to View Structure
Identification— Dilute a volume of Rectal Solution, equivalent to about 500 mg of aminophylline, with water to about 20 mL, and add, with constant stirring, 1 mL of 3 N hydrochloric acid or sufficient to precipitate the theophylline completely. Filter, wash with small portions of cold water until free from chloride, and dry at 105 for 4 hours. Use the precipitate and the filtrate for the following tests.
B: The filtrate obtained as directed above meets the requirements for Identification test C under Aminophylline.
pH 791: between 9.0 and 9.5.
Ethylenediamine content— Measure accurately a volume of Rectal Solution, equivalent to about 500 mg of aminophylline, and dilute with water, if necessary, to make about 30 mL. Add methyl orange TS, and titrate with 0.1 N hydrochloric acid VS. Each mL of 0.1 N hydrochloric acid is equivalent to 3.005 mg of C2H8N2. The Rectal Solution contains between 218 mg and 267 mg of ethylenediamine (C2H8N2) per g of anhydrous theophylline (C7H8N4O2) found in the Assay.
Standard preparation— Dissolve an accurately weighed quantity of USP Theophylline RS in dilute hydrochloric acid (1 in 100), and dilute quantitatively and stepwise with the same solvent to obtain a solution having a known concentration of about 8 µg per mL.
Assay preparation— Pipet an accurately measured volume of Rectal Solution, equivalent to about 500 mg of aminophylline, into a 500-mL volumetric flask, dilute with water to volume, and mix. Pipet 5 mL of this solution into a second 500-mL volumetric flask, add 50 mL of dilute hydrochloric acid (1 in 10), dilute with water to volume, and mix.
Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 270 nm, with a suitable spectrophotometer, using dilute hydrochloric acid (1 in 100) as the blank. Calculate the quantity, in mg, of anhydrous theophylline (C7H8N4O2) in each mL of the Rectal Solution taken by the formula:
50(C/V)(AU / AS)
in which C is the concentration, in µg per mL, of USP Theophylline RS in the Standard preparation; V is the volume, in mL, of Rectal Solution taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.
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Monograph Domenick Vicchio, Ph.D.
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