Tolnaftate

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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C₁₉H₁₇NOS        307.41

Carbamothioic acid, methyl(3-methylphenyl)-, O-2-naphthalenyl ester.

O-2-Naphthyl m,N-dimethylthiocarbanilate CAS RN: 2398-96-1; UNII: 06KB629TKV.

Tolnaftate contains not less than 98.0 percent and not more than 102.0 percent of C₁₉H₁₇NOS, calculated on the dried basis.

Packaging and storage-Preserve in tight containers.

USP REFERENCE STANDARDS (11)

USP Tolnaftate RS

1 Identification

Change to read:

A: Spectroscopic Identification Tests (197), Infrared Spectroscopy: 197K _{(CN 1-May-2020)}

B: The UV absorption spectrum of the solution employed for measurement of absorbance in the Assay exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Tolnaftate RS, concomitantly measured.

C: Prepare a test solution by dissolving 10 mg in 10 mL of alcohol. Apply 10 µL of this test solution and 10 µL of a Standard solution of USP Tolnaftate RS in alcohol having a concentration of 1.0 mg per ml to a thin-layer chromatographic plate (see Chromatography (621)) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram, using toluene as the solvent system, until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, allow the solvent to evaporate, and view under short-wavelength UV light: the R, value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

MELTING RANGE (741): between 110° and 113°.

LOSS ON DRYING (731)-Dry it in vacuum at 65° for 3 hours: it loses not more than 0.5% of its weight.

RESIDUE ON IGNITION (281): not more than 0.1%,

2 Assay

Dissolve about 50 mg of Tolnaftate, accurately weighed, in methanol, and dilute the solution quantitatively and stepwise with methanol to obtain a concentration of about 10 µg per mL. Dissolve an accurately weighed quantity of USP Tolnaftate RS in methanol, and dilute quantitatively and stepwise with methanol to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 258 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of C₁₉H₁₇NOS in the portion of Tolnaftate taken by the formula:

5C(A_u /A_s )

in which C is the concentration, in µg per mL, of USP Tolnaftate RS in the Standard solution, and A_u and A_s are the absorbances of the solution of Tolnaftate and the Standard solution, respectively.