Aminophylline Injection

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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1 DEFINITION

Aminophylline Injection is a sterile solution of Aminophylline in Water for Injection, or is a sterile solution of Theophylline in Water for Injection prepared with the aid of Ethylenediamine. It contains, in each mL, an amount of aminophylline (C₁₆H₂₄N₁₀O₄) equivalent to NLT 93.0% and NMT 107.0% of the labeled amount of anhydrous theophylline (C₇H₈N₄O₂).

Aminophylline Injection may contain an excess of Ethylenediamine, but no other substance may be added for the purpose of pH adjustment. [Note—Do not use the Injection if crystals have separated.]

2 IDENTIFICATION

A.

Analysis: Dilute a volume of Injection equivalent to 500 mg of aminophylline with water to 20 mL, and add, with constant stirring, 1 mL of 3 N hydrochloric acid or enough to completely precipitate the theophylline, and filter. To the filtrate 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 precipitate melts at 164°–171°.

Change to read:

B. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020)

Analysis: Wash the precipitated theophylline from Identification A 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.

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

3 ASSAY

Procedure

Solution A: 10 mM ammonium acetate prepared as follows. Transfer 770.8 mg of ammonium acetate to a 1-L volumetric ask, and dissolve in water to 80% of the ask 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 ask, 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: Nominally 0.17 mg/mL of anhydrous theophylline in water prepared as follows. Transfer 8.5 mg of anhydrous theophylline from a volume of Injection to a 50-mL volumetric ask. Dissolve and dilute with water to volume.

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 270 nm

Column: 2.1-mm × 10-cm; 1.7-µm packing L1

Column temperature: 40°

Flow rate: 0.4 mL/min

Injection volume: 1 µL

3.2 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 1.0%, Standard solution

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of theophylline (C₇H₈N₄O₂) in the portion of Injection taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 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 = nominal concentration of theophylline in the Sample solution (mg/mL)

Acceptance criteria: 93.0%–107.0%

4 OTHER COMPONENTS

Content of Ethylenediamine

Sample: A volume of Injection equivalent to 500 mg of aminophylline

Diluent: Water

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N hydrochloric acid VS

Endpoint detection: Visual

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

Acceptance criteria: 166–192 mg of ethylenediamine (C₂H₈N₂) per gram of theophylline (C₇H₈N₄O₂) found in the Assay

5 IMPURITIES

Organic Impurities

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

Standard solution: 2.0 µg/mL each of USP Theophylline RS and USP Theophylline Related Compound D RS in water Sample solution: Nominally 1.0 mg/mL of anhydrous aminophylline in water prepared as follows. Transfer 25 mg of anhydrous aminophylline from a volume of Injection to a 25-mL volumetric ask. Dissolve and dilute with water to volume.

5.1 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

5.2 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of theophylline related compound D in the portion of Injection taken:

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

r_U = peak response of theophylline related compound D from the Sample solution

r_S = peak response of theophylline related compound D from the Standard solution

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

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

Calculate the percentage of any other individual unspecified degradation product in the portion of Injection taken:

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

U S S U

r_U = peak response of any other individual unspecified degradation product 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 = nominal concentration of aminophylline in the Sample solution (mg/mL)

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

Table 2

^a Process impurity included for identification only and not to be included in the calculation of total degradation products.

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

^c 3-Methyl-1H-purine-2,6-dione.

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

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

6 SPECIFIC TESTS

pH 〈791〉: 8.6–9.0

Particulate Matter in Injections 〈788〉: Meets the requirements for small-volume injections

Other Requirements: Meets the requirements in Injections and Implanted Drug Products 〈1〉

Bacterial Endotoxins Test 〈85〉: It contains NMT 1.0 USP Endotoxin Unit/mg of aminophylline.

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in single-dose containers from which carbon dioxide has been excluded, preferably of Type I glass, protected from light. Store at controlled room temperature.

Labeling: Label the Injection to state the content of anhydrous theophylline.

USP Reference Standards 〈11〉

USP Theophylline RS

USP Theophylline Related Compound D RS

Theophylline;

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

C₆H₁₀N₄O · HCl · H₂O     208.65

USP Theophylline Related Compound F RS

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

C₉H₁₂N₄O₃      224.22