Aminophylline

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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C₁₆H₂₄N₁₀O₄ 420.43

C₁₆H₂₄N₁₀O₄·2H2O 456.46

1H-Purine-2,6-dione, 3,7-dihydro-1,3-dimethyl-, compd. with 1,2-ethanediamine (2:1); Theophylline compound with ethylenediamine (2:1).

Anhydrous CAS RN^®: 317-34-0; UNII: 27Y3KJK423.

Dihydrate CAS RN^®: 5897-66-5; UNII: C229N9DX94.

1 DEFINITION

Aminophylline is anhydrous or contains NMT two molecules of water of hydration. It contains NLT 84.0% and NMT 87.4% of anhydrous theophylline (C₇H₈N₄O₂), calculated on the anhydrous basis.

2 IDENTIFICATION

Change to read:

A. SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197A or 197K. (CN 1-May-2020)

Sample: 500 mg of Aminophylline

Analysis: Dissolve the Sample in 20 mL of water, add, with constant stirring, 1 mL of 3 N hydrochloric acid, filter (retain the filtrate), wash the precipitate with small portions of cold water, and dry at 105° for 1 h.

Acceptance criteria: The IR spectrum of theophylline so obtained corresponds to that of USP Theophylline RS.

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

C.

Sample: The filtrate obtained in Identification A.

Analysis: To the Sample add 0.5 mL of benzenesulfonyl chloride and 5 mL of 1 N sodium hydroxide to render alkaline. Shake by mechanical means for 10 min, add 5 mL of 3 N hydrochloric acid to acidify, chill, collect the precipitated disulfonamide of ethylenediamine, wash with water, recrystallize from water, and dry at 105° for 1 h.

Acceptance criteria: The dried precipitate melts at 164°-171°.

3 ASSAY

3.1 PROCEDURE

Solution A: 10 mM ammonium acetate prepared as follows. Transfer 770.8 mg of ammonium acetate to a 1-L volumetric flask, and dissolve in water to 80% of the flask volume. Adjust with glacial acetic acid to a pH of 5.5, and dilute with water to volume. Pass through a suitable filter of 0.2-µm pore size.

Solution B: Methanol

Mobile phase: See Table 1.

Table 1

Impurity stock solution: 25 µg/mL of USP Theophylline Related Compound F RS in water

System suitability solution: 0.8 mg/mL of USP Theophylline RS and 1 µg/mL of USP Theophylline Related Compound F RS in water prepared as follows. Transfer 21 mg of USP Theophylline RS to a 25-mL volumetric flask and add 15 mL of water. Sonicate to dissolve, add 1 mL of Impurity stock solution, and dilute with water to volume.

Standard solution: 0.17 mg/mL of USP Theophylline RS in water. Sonicate to dissolve as needed.

Sample solution: 0.2 mg/mL of Aminophylline in water

3.2 Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 270 nm

Column: 2.1-mm x 10-cm; 1.7-um packing L1

Column temperature: 40°

Flow rate: 0.4 mL/min

Injection volume: 1 µL

3.3 System suitability

Samples: System suitability solution and Standard solution

Suitability requirements

Resolution: NLT 2.0 between theophylline and theophylline related compound F, System suitability solution

Relative standard deviation: NMT 0.73%, Standard solution

3.4 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of theophylline (C₇H₈N₄O₂) in the portion of Aminophylline taken:

Result = (r_U/r_S) x (C_S/C_U) x 100

r_U = peak response of theophylline from the Sample solution

r_S = peak response of theophylline from the Standard solution

C_S = concentration of USP Theophylline RS in the Standard solution (mg/mL)

C_U = concentration of Aminophylline in the Sample solution (mg/mL)

Acceptance criteria: 84.0%-87.4% of theophylline on the anhydrous basis

4 OTHER COMPONENTS

CONTENT OF ETHYLENEDIAMINE

Sample: 500 mg of Aminophylline

Diluent: Water

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N hydrochloric acid VS

Endpoint detection: Visual

Analysis: Dissolve the Sample in 30 mL of Diluent, add methyl orange TS, and titrate. Each mL of 0.1 N hydrochloric acid is equivalent to 3.005 mg of ethylenediamine (C₂H₈N₂).

Acceptance criteria: 157-175 mg of ethylenediamine (C₂H₈N₂) per gram of theophylline (C₇H₈N₄O₂) found in the Assay

5 IMPURITIES

5.1 RESIDUE ON IGNITION (281)

NMT 0.15%

5.2 ORGANIC IMPURITIES

Solution A, Solution B, Mobile phase, System suitability solution, and Chromatographic system: Proceed as directed in the Assay.

Standard stock solution: 25.0 µg/mL each of USP Caffeine RS, USP Theophylline RS, USP Theophylline Related Compound B RS, USP Theophylline Related Compound C RS, USP Theophylline Related Compound D RS, and USP Theophylline Related Compound F RS in water

Standard solution: 1.0 µg/mL each of USP Caffeine RS, USP Theophylline RS, USP Theophylline Related Compound B RS, USP Theophylline Related Compound C RS, USP Theophylline Related Compound D RS, and USP Theophylline Related Compound F RS in water, from Standard stock solution

Sample solution: 1.0 mg/mL of Aminophylline in water

System suitability

Samples: System suitability solution and Standard solution

[NOTE-See Table 2 for the relative retention times.]

Suitability requirements

Resolution: NLT 2.0 between theophylline and theophylline related compound F, System suitability solution

Relative standard deviation: NMT 3.0% for each peak, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of caffeine, theophylline related compound B, theophylline related compound C, theophylline related compound D, and theophylline related compound F in the portion of Aminophylline taken:

Result = (r_U/r_S) x (C_S/C_U) x 100

r_U = peak response of caffeine, theophylline related compound B, theophylline related compound C, theophylline related compound D, or theophylline related compound F from the Sample solution

r_S = peak response of the corresponding Reference Standard from the Standard solution

C_S = concentration of the corresponding Reference Standard in the Standard solution (mg/mL)

C_U = concentration of Aminophylline in the Sample solution (mg/mL)

Calculate the percentage of dimethyl uric acid, theobromine, and any other individual unspecified impurity in the portion of Aminophylline taken:

Result = (r_U/r_S) x (C_S/C_U) x (1/F) 100

r_U = peak response of dimethyl uric acid, theobromine, or any other individual unspecified impurity from the Sample solution

r_S = peak response of theophylline from the Standard solution

C_S = concentration of USP Theophylline RS in the Standard solution (mg/mL)

C_U = concentration of Aminophylline in the Sample solution (mg/mL)

F = relative response factor

Acceptance criteria: See Table 2. Disregard peaks less than 0.05%.

Table 2

^a 1,3-Dimethyl-7,9-dihydro-1H-purine-2,6,8(3H)-trione.

^b 3,7-Dihydro-3,7-dimethylpurine-2,6(1H)-dione.

6 SPECIFIC TESTS

WATER DETERMINATION (921), Method I

Sample: 1.5 g of Aminophylline

Solvent: 50 mL of chloroform and anhydrous methanol (50:50) in place of anhydrous methanol

Acceptance criteria

Anhydrous: NMT 0.75%

Hydrous: NMT 7.9%

7 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers. Store at controlled room temperature.

LABELING: Label it to indicate whether it is anhydrous or hydrous, and also to state the content of anhydrous theophylline.

USP REFERENCE STANDARDS (11).

USP Caffeine RS

USP Theophylline RS

USP Theophylline Related Compound B RS

3-Methyl-1H-purine-2,6-dione;

Also known as 3-Methyl-3,7-dihydro-1H-purine-2,6-dione.

C₆H₆N₄O₂ 166.14

USP Theophylline Related Compound C RS

N-(6-Amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-yl)formamide.

C₇H₁₀N₄O₃ 198.18

USP Theophylline Related Compound D RS

Theophyllidine;

N-Methyl-5-(methylamino)-1H-imidazole-4-carboxamide hydrochloride monohydrate.

C₆H₁₀N₄O·HCl·H₂O 208.65

USP Theophylline Related Compound FRS

7-(2-Hydroxyethyl)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione .

C₉H₁₂N₄O₃ 224.22