Pimobendan

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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C₁₉H₁₈N₄O₂             334.37

3(2H)-Pyridazinone, 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]-5-methyl-, (±)-; (±)-4,5-Dihydro-6-[2-(p-methoxyphenyl)-5-benzimidazolyl]-5-methyl-3(2H)-pyridazinone;

6-[2-(4-Methoxyphenyl)-1H-benzimidazol-5-yl]-5-methyl-4,5-dihydropyridazin-3(2H)-one CAS RN®: 74150-27-9.

1 DEFINITION

Pimobendan contains NLT 98.0% and NMT 102.0% of pimobendan (C₁₉H₁₈N₄O₂), calculated on the anhydrous basis. 

2 IDENTIFICATION

Change to read:

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

B. 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: 3.0 g/L of monobasic potassium phosphate in water. Adjust with suitably diluted phosphoric acid to a pH of 2.5. Solution B: Acetonitrile

Mobile phase: See Table 1.

Table 1

Standard solution: 0.1 mg/mL of USP Pimobendan RS in methanol

Sample solution: 0.1 mg/mL of Pimobendan in methanol

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 290 nm

Column: 4.6-mm × 12.5-cm; 5-µm packing L1 or 4.0-mm × 12.5-cm; 5-µm packing L1

Column temperature: 45°

Flow rate: 1 mL/min

Injection volume: 10 µL

3.2 System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 0.73%

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of pimobendan (C₁₉H₁₈N₄O₂) in the portion of Pimobendan taken: 

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

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

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

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

Acceptance criteria: 98.0%–102.0% on the anhydrous basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Organic Impurities

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

System suitability solution: 5 µg/mL each of USP Pimobendan Related Compound A RS and USP Pimobendan Related Compound B RS in methanol

Standard solution: 50 µg/mL of USP Pimobendan RS in methanol

Sample solution: 5.0 mg/mL of Pimobendan in methanol

4.1 System suitability

Samples: System suitability solution and Standard solution

Suitability requirements

Resolution: NLT 2.0 between pimobendan related compound A and pimobendan related compound B, System suitability solution Tailing factor: 0.8–1.5, Standard solution

4.2 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of Pimobendan taken:

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

r_U = peak response of each impurity from the Sample solution

r_S = peak response of pimobendan from the Standard solution

C_S = concentration of USP Pimobendan RS in the Standard solution (µg/mL)

C_U = concentration of Pimobendan in the Sample solution (µg/mL)

Acceptance criteria: See Table 2. Disregard any peak below 0.05%.

Table 2

5 SPECIFIC TESTS

Water Determination 〈921〉, Method I

Sample: 0.5 g

Acceptance criteria: NMT 1.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers and store at room temperature.

Labeling: Label it to indicate that it is for veterinary use only.

USP Reference Standards 〈11〉

USP Pimobendan RS

USP Pimobendan Related Compound A RS

4-[2-(4-Methoxyphenyl)-1H-benzimidazol-5-yl]-3-methyl-4-oxobutanoic acid.

C₁₉H₁₈N₂O₄          338.36

USP Pimobendan Related Compound B RS

N-[2-Amino-4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)phenyl]-4-methoxybenzamide.

C₁₉H₂₀N₄O₃        352.39