Tolnaftate Gel

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

Tolnaftate Gel contains NLT 90.0% and NMT 110.0% of the labeled amount of tolnaftate (C₁₉H₁₇NOS).

2 IDENTIFICATION

2.1 A.

Standard solution: 1 mg/mL of USP Tolnaftate RS in alcohol

Sample stock solution: Use the Sample stock solution prepared in the Assay.

Sample solution: Nominally 1 mg/mL of tolnaftate prepared as follows: Evaporate 10 mL of the Sample stock solution on a steam bath just to dryness, and dissolve the residue in 1 mL of alcohol.

Chromatographic system

• (See Chromatography 〈621〉, General Procedures, Thin-Layer Chromatography.)
• Mode: TLC
• Absorbent: 0.25-mm layer of chromatographic silica gel mixture
• Developing solvent system: Toluene
• Application volume: 10 μL

Analysis

Samples: Standard solution and Sample solution

Proceed as directed in the chapter. Allow the spots to dry and develop the chromatogram in the Developing solvent system until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber and view under short-wavelength UV light.

Acceptance criteria: The R_F value of the principal spot from the Sample solution corresponds to that from the Standard solution.

3 ASSAY

3.1 Procedure

Standard solution: 10 μg/mL of USP Tolnaftate RS in chloroform

Sample stock solution: Nominally 0.1 mg/mL of tolnaftate prepared as follows. Transfer a portion of Gel, equivalent to 10 mg of tolnaftate, into a 250-mL separator containing 75 mL of chloroform. Wash the chloroform solution successively with two 25-mL portions of 0.1 N sodium hydroxide VS, two 25-mL portions of 0.1 N hydrochloric acid VS, and 25 mL of water. Transfer the chloroform layer to a 100-mL volumetric flask, and dilute with chloroform to volume. [Note—Reserve a 10-mL portion of this solution for Identification A.]

Sample solution: Nominally 10 μg/mL of tolnaftate in chloroform from the Sample stock solution

Instrumental conditions

• Mode: UV
• Analytical wavelength: 258 nm
• Cell: 1 cm
• Blank: Chloroform

Analysis

Samples: Standard solution, Sample solution, and Blank

Calculate the percentage of the labeled amount of tolnaftate (C₁₉H₁₇NOS) in the portion of Gel taken:

Result = (Aᵤ/Aₛ) × (Cₛ/Cᵤ) × 100

Aᵤ = absorbance of the Sample solution

Aₛ = absorbance of the Standard solution

Cₛ = concentration of USP Tolnaftate RS in the Standard solution (μg/mL)

Cᵤ = nominal concentration of tolnaftate in the Sample solution (μg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

Minimum Fill 〈755〉: Meets the requirements

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

USP Reference Standards 〈11〉

USP Tolnaftate RS