Diclazuril

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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C₁₇H₉Cl₃N₄O₂   407.64

Benzeneacetonitrile, 2,6-dichloro-α-(4-chlorophenyl)-4-(4,5-dihydro-3,5-dioxo-1,2,4-triazin-2(3H)-yl)-;

(p-Chlorophenyl)[2,6-dichloro-4-(4,5-dihydro-3,5-dioxo-as-triazin-2(3H)-yl)phenyl]acetonitrile  CAS RN®: 101831-37-2; UNII: K110K1B1VE

1 DEFINITION

Diclazuril contains NLT 97.0% and NMT 101.0% of C₁₇H₉Cl₃N₄O₂, calculated on the dried basis.

2 IDENTIFICATION

Change to read:

Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K

3 ASSAY

3.1 Procedure

Buffer: Dissolve 6.3 g of ammonium formate in 800 mL of water, adjust with anhydrous formic acid to a pH of 4.0, and add 200 mL of water.

Solution A: Acetonitrile, water, and Buffer (3:15:2)

Solution B: Acetonitrile, water, and Buffer (85:5:10)

Mobile phase: See the gradient table below.

Standard solution: 0.5 mg/mL of USP Diclazuril RS in dimethylformamide

System suitability solution: 0.5 mg/mL of USP Diclazuril System Suitability Mixture RS in dimethylformamide

Sample solution: 0.5 mg/mL of Diclazuril in dimethylformamide

Chromatographic system

• (See Chromatography 〈621〉, System Suitability.)
• Mode: LC
• Detector: UV 230 nm
• Column: 4.6-mm × 10-cm; base-deactivated 3-µm packing L1
• Flow rate: 1 mL/min
• Column temperature: 35°
• Injection size: 5 µL

System suitability

• Samples: Standard solution and System suitability solution
• Suitability requirements
• Resolution: NLT 1.9 between diclazuril and diclazuril ketone peaks, System suitability solution
• Tailing factor: NMT 1.4, Standard solution
• Relative standard deviation: NMT 2.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of C₁₇H₉Cl₃N₄O₂ in the portion of Diclazuril taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response from the Sample solution

rₛ = peak response from the Standard solution

Cₛ = concentration of USP Diclazuril RS in the Standard solution (mg/mL)

Cᵤ = concentration of Diclazuril in the Sample solution (mg/mL)

Acceptance criteria: 97.0%–101.0% on the dried basis

4 IMPURITIES

4.1 Inorganic Impurities

4.1.1 Residue On Ignition 〈281〉: NMT 0.1%

4.2 Organic Impurities

4.2.1 Procedure 1: Residual Solvents 〈467〉

Acceptance criteria: NMT 4000 ppm of N,N-dimethylformamide

4.2.2 Procedure 2

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

Analysis

Samples: Standard solution and Sample solution

Calculate the area percentage of each impurity, relative to diclazuril, in the portion of Diclazuril taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × (1/F) × 100

rᵤ = peak response of each impurity from the Sample solution

rₛ = peak response of diclazuril from the Standard solution

Cₛ = concentration of USP Diclazuril RS in the Standard solution (mg/mL)

Cᵤ = concentration of Diclazuril in the Sample solution (mg/mL)

F = relative response factor (see Impurity Table 1)

Acceptance criteria

[Note-Disregard any peak observed in the blank. The reporting level for impurities is 0.05%.]

Individual impurities: See Impurity Table 1.

Total impurities: NMT 1.5%

Impurity Table 1

ᵃ (RS)-2-[3,5-Dichloro-4-[(4-chlorophenyl)cyanomethyl]phenyl]-3,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carboxylic acid.

ᵇ (RS)-2-[3,5-Dichloro-4-[(4-chlorophenyl)cyanomethyl]phenyl]-3,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carboxamide.

ᶜ 2-[3,5-Dichloro-4-(4-chlorobenzoyl)phenyl]-1,2,4-triazine-3,5(2H,4H)-dione.

ᵈ (RS)-2-(4-Amino-2,6-dichlorophenyl)-2-(4-chlorophenyl)acetonitrile.

ᵉ 2-[3,5-Dichloro-4-(4-chlorobenzyl)phenyl]-1,2,4-triazine-3,5(2H,4H)-dione.

ᶠ (RS)-2-(4-Chlorophenyl)-2-(2,6-dichlorophenyl)acetonitrile.

5 SPECIFIC TESTS

Loss On Drying, 〈731〉: Dry a sample at between 100° and 105° under a vacuum for 4 h: it loses NMT 0.5% of its weight.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, and store at room temperature.

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

USP Reference Standards 〈11〉

• USP Diclazuril RS
• USP Diclazuril System Suitability Mixture RS

Contains diclazuril and specified impurities.