Finasteride

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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C₂₃H₃₆N₂O₂ 372.54

4-Azaandrost-1-ene-17-carboxamide, N-(1,1-dimethylethyl)-3-oxo-, (5α,17β)-.

N-tert-Butyl-3-oxo-4-aza-5α-androst-1-ene-17β-carboxamide CAS RN®: 98319-26-7; UNII: 57GNO57U7G.

Finasteride contains not less than 98.5 percent and not more than 101.0 percent of C₂₃H₃₆N₂O₂, calculated on the anhydrous basis.

1 Packaging and storage

Preserve in tight containers, and store at controlled room temperature.

USP Reference standards 〈11〉

USP Finasteride RS

2 Identification

Change to read:

A: Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197M (CN 1-May-2020) .

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Specific rotation 〈781S〉: between −56.0° and −60.0°, determined at 405 nm.

Test solution: 10 mg per mL, in methanol.

Water Determination, Method I 〈921〉: not more than 0.3%.

Residue on ignition 〈281〉: not more than 0.1%.

3 Chromatographic purity

Mobile phase - Prepare a filtered and degassed mixture of water, tetrahydrofuran, and acetonitrile (8:1:1). Make adjustments if necessary (see System Suitability under Chromatography 〈621〉).

Diluting solution - Prepare a solution of water and acetonitrile (1:1).

Standard solution - Dissolve an accurately weighed quantity of USP Finasteride RS in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 1.0 mg per mL.

Test solution - Transfer about 100 mg of Finasteride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Diluting solution to volume, and mix.

Chromatographic system (see Chromatography 〈621〉) - The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 30-cm column that contains 4-μm packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 60°.

Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the column efficiency is not less than 10,000 theoretical plates; and the tailing factor is not more than 1.3.

Procedure Inject a volume (about 15 μL) of the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of each impurity in the portion of Finasteride taken by the formula:

100 (r_i /r_S)

in which r_i is the peak response for each impurity, and r_S is the sum of the responses of all peaks: not more than 0.5% of any individual impurity is found; and not more than 1.0% of total impurities is found.

4 Assay

Mobile phase - Prepare a filtered and degassed mixture of water and tetrahydrofuran (4:1). Make adjustments if necessary (see System

Suitability under Chromatography 〈621〉).

Diluting solution - Prepare a solution of water and acetonitrile (1:1).

Standard preparation - Dissolve an accurately weighed quantity of USP Finasteride RS in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 200 μg per mL.

Assay preparation - Transfer about 20 mg of Finasteride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Diluting solution to volume, and mix.

Chromatographic system (see Chromatography 〈621〉) - The liquid chromatograph is equipped with a 215-nm detector and a 3.0-mm × 3.0-cm column that contains 3-μm packing L7. The flow rate is about 3 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1800 theoretical plates; the tailing factor is not more than 1.3; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure - Separately inject equal volumes (about 10 μL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C₂₃H₃₆N₂O₂ in the portion of Finasteride taken by the formula:

100C(r_U /r_S )

in which C is the concentration, in mg per mL, of USP Finasteride RS in the Standard preparation; and r_U and r_S are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.