Monensin Type A Medicated Article

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

Monensin Type A Medicated Article contains Monensin Granulated mixed with suitable diluents and inactive ingredients. It contains the equivalent of NLT 85.0% and NMT 115.0% of the labeled amount of monensin.

2 IDENTIFICATION

A. The retention times of the major peak for monensin A and minor peak for monensin B of the Sample solution correspond to those of the Standard solution, as obtained in the Assay.

3 ASSAY

3.1 Procedure

Mobile phase: Methanol, glacial acetic acid, and water (940:1:60)

Neutralized methanol: Add 1 g of sodium bicarbonate to 4 L of methanol, mix, and filter.

Diluent: Methanol and water (9:1)

Derivatizing reagent: Dissolve 3 g of vanillin in a mixture of 95 mL of methanol and 2 mL of sulfuric acid. [Caution-To avoid splattering, add the sulfuric acid carefully and slowly with a pipet; do not pour. Allow the mixture of methanol and sulfuric acid to cool before adding vanillin.]

System suitability solution: 1 mg/mL of USP Monensin Sodium RS and 3 mg/mL of USP Narasin RS in Neutralized methanol. Dilute 2 mL of this solution with Diluent to 200 mL.

Standard stock solution: 1000 µg/mL of monensin from USP Monensin Sodium RS in methanol

Standard solution: 20 µg/mL of monensin from Standard stock solution in Diluent

Sample stock solution: Dilute 5 g of Monensin Type A Medicated Article in 200.0 mL of Diluent, and shake by mechanical means for 1 h. Allow the solids to settle.

Sample solution: Nominally 20 µg/mL of monensin, from the clear supernatant of the Sample stock solution, in Diluent

Chromatographic system

• (See Chromatography 〈621〉, System Suitability.)
• Mode: LC
• Detector: UV 520 nm
• Column: 4.6-mm × 25-cm; packing L1. The column outlet is attached to a tee, the opposing arm is attached to a tube from which is pumped the Derivatizing reagent, and the outlet is connected to a 2-mL postcolumn reaction coil maintained at 98°. The outlet of the reaction coil is connected to the Detector.
• Flow rate: 0.7 mL/min for Mobile phase and Derivatizing reagent
• Injection volume: 200 µL

System suitability

• Samples: System suitability solution and Standard solution
• [Note-The relative retention times for monensin B, monensin A, narasin A, and narasin I are about 0.9, 1.0, 1.3, and 1.5, respectively.]
• Suitability requirements
• Resolution: NLT 1.25 between the monensin B and the monensin A peaks; NLT 3.5 between the monensin A and the narasin A peaks, System suitability solution
• Tailing factor: NMT 1.4, Standard solution
• Relative standard deviation: NMT 2.0%, Standard solution
• [Note-After use, flush the system with methanol.]

Analysis

Samples: Standard solution and Sample solution

[Note-Use peak areas where peak responses are indicated.]

Measure the responses for the major peaks, including a peak for monensin C/D, if present, at a retention time of 1.1 relative to that of the main monensin A peak in the chromatogram from the Sample solution.

Calculate the quantity, in mg, of monensin A, monensin B, and monensin C/D in each g of Monensin Type A Medicated Article taken:

Result = (rᵤ/rₛ) × (Cₛ × F × D)/(100,000 × W)

rᵤ = peak response of monensin A, monensin B, or monensin C/D from the Sample solution

rₛ = peak response of monensin A from the Standard solution

Cₛ = concentration of monensin activity in the Standard solution, based on the quantity of USP Monensin Sodium RS taken, its designated potency (µg/mg) and extent of dilution (µg/mL)

F = designated percentage of monensin A in USP Monensin Sodium RS

D = dilution factor used in preparing the Sample solution

W = quantity of Monensin Type A Medicated Article taken to prepare the Sample solution (g)

Calculate the potency, in mg, of monensin in each g of Monensin Type A Medicated Article taken:

Result = (A × F_A) + (B × F_B) + (C/D × F_C/D)

A = quantity of monensin A in each g of Monensin Type A Medicated Article taken, as calculated previously (mg)

F_A = biopotency conversion factor for monensin A, 1.00

B = quantity of monensin B in each g of Monensin Type A Medicated Article taken, as calculated previously (mg)

F_B = biopotency conversion factor for monensin B, 0.28

C/D = quantity of monensin C/D in each g of Monensin Type A Medicated Article taken, as calculated previously (mg)

F_C/D = biopotency conversion factor for monensin C/D, 1.50

Acceptance criteria: 85.0%–115.0%

4 SPECIFIC TESTS

4.1 Loss on Drying 〈731〉

Analysis: Dry under vacuum at 60° for 2 h.

Acceptance criteria: NMT 10%

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers. Avoid moisture and excessive heat.

Labeling: Label it to indicate that it is for veterinary use only. The label bears the statement “Do not feed undiluted”.

USP Reference Standards 〈11〉

USP Monensin Sodium RS

USP Narasin RS