Tolnaftate Topical Solution
» Tolnaftate Topical Solution contains not less than 90.0 percent and not more than 115.0 percent of the labeled amount of C19H17NOS.
Packaging and storage— Preserve in tight containers.
Identification— Evaporate 25 mL of the next-to-final chloroform solution prepared in the Assay on a steam bath just to dryness, and dissolve the residue in 1 mL of alcohol. Using this as the test solution, proceed as directed in Identification test C under Tolnaftate: the specified result is observed.
Assay— Pipet into a separator a volume of Topical Solution, equivalent to about 10 mg of tolnaftate, add 50 mL of chloroform, and extract with 50 mL of 0.1 N sodium hydroxide. Filter the chloroform layer through a chloroform-washed cotton pledget into a 250-mL volumetric flask, and extract the aqueous layer with two 45-mL portions of chloroform, filtering each portion into the flask. Add chloroform to volume, and mix. [note—Reserve a 25-mL portion of this solution for the Identification test.] Dilute 25.0 mL of the solution with chloroform to 100.0 mL, and mix. Dissolve an accurately weighed quantity of USP Tolnaftate RS in chloroform, and dilute quantitatively and stepwise with chloroform 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 chloroform as the blank. Calculate the quantity, in mg, of C19H17NOS in each mL of Topical Solution taken by the formula:
(C / V)(AU / AS)
in which C is the concentration, in µg per mL, of USP Tolnaftate RS in the Standard solution, V is the volume, in mL, of Topical Solution taken, and AU and AS are the absorbances of the solution from the Topical Solution and the Standard solution, respectively.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Behnam Davani, Ph.D., M.B.A.
Senior Scientist
(MDAA05) Monograph Development-Antivirals and Antimicrobials
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 3773