Minoxidil Tablets

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

Minoxidil Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of minoxidil (C₉H₁₅N₅O).

2 IDENTIFICATION

A. The retention time of the minoxidil peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

B. The UV absorption spectra of the minoxidil peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

PROCEDURE

Mobile phase: Methanol, glacial acetic acid, and water (70:1:30). Add 3.0 g/L of Docusate sodium, and adjust with perchloric acid to a pH of 3.0.

Standard solution: 0.25 mg/mL of USP Minoxidil RS in Mobile phase

Sample solution: Nominally 0.25 mg/mL of minoxidil in Mobile phase prepared as follows. Dissolve the equivalent to 5 mg of minoxidil, from a portion of powdered Tablets (NLT 10), in 20.0 mL of Mobile phase, and shake for 5 min.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 254 nm. For Identification B, use a diode array detector in the range of 200-400 nm.

Column: 4-mm x 25-cm; 5-µm packing L1

Flow rate: 1 mL/min

Injection volume: 10 µL

Run time: NLT 2 times the retention time of the minoxidil peak

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of minoxidil (C₉H₁₅N₅O) in the portion of Tablets taken:

Result = (r_u /r_s ) × (C_s /C_u ) × 100

r_u = peak response of minoxidil from the Sample solution

r_s = peak response of minoxidil from the Standard solution

C_s = concentration of USP Minoxidil RS in the Standard solution (mg/mL)

C_u = nominal concentration of minoxidil in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

DISSOLUTION (711)

Medium: pH 7.2 phosphate buffer (see Reagents. Indicators, and Solutions-Solutions, Buffer Solutions); 900 mL.

Apparatus 1: 75 rpm

Time: 15 min

Standard solution: A known concentration of USP Minoxidil RS in Medium.

Sample solution: Dilute with Medium to a concentration that is similar to that of the Standard solution..

Instrumental conditions

Mode: UV

Detector: UV 231 nm for Tablets containing up to 10 mg of minoxidil; UV 287 nm for Tablets containing more than 10 mg of minoxidil

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of minoxidil (C₉H₁₅N₅O) dissolved:

Result = (A_u /A_s ) × C_s × D × (V/L) × 100

A_u = absorbance of the Sample solution

A_s = absorbance of the Standard solution

C_s = concentration of USP Minoxidil RS in the Standard solution (mg/mL)

D = dilution factor for the Sample solution

V = volume of the Medium, 900 mL

L = label claim (mg/Tablet)

Tolerances: NLT 75% (Q) of the labeled amount of minoxidil (C₉H₁₅N₅O) is dissolved.

UNIFORMITY OF DOSAGE UNITS (905): Meet the requirements

5 IMPURITIES

Change to read:

ORGANIC IMPURITIES

Mobile phase: Dissolve 2.0 g of sodium lauryl sulfate in a mixture of 600 mL of methanol, 10 mL of glacial acetic acid, and 400 mL of water.

Adjust with perchloric acid to a pH of 3.0 ±0.1, and pass through a suitable filter of 0.45-µm pore size.

Diluent: Methanol and water (50:50)

Standard solution: 0.005 mg/mL of USP Minoxidil RS in Diluent

Sensitivity solution: 0.25 µg/mL of USP Minoxidil RS in Diluent from Standard solution

Sample solution: Nominally 0.25 mg/mL of minoxidil in Diluent from NLT 20 powdered Tablets. Transfer a suitable amount of the powdered Tablets in an appropriate volumetric flask. Initially add Diluent to about 60% of the flask volume, shake on a mechanical shaker for 20 min, and then dilute with Diluent to volume. Pass through a suitable filter of 0.45-µm pore size.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.9-mm x 15-cm; 3- to 10-um packing L1

Flow rate: 0.5 mL/min

Injection volume: 40 µL

System suitability

Samples: Standard solution and Sensitivity solution

Suitability requirements

Tailing factor: NMT 2.0, Standard solution

Relative standard deviation: NMT 2.0%, Standard solution

Signal-to-noise ratio: NLT 10, Sensitivity solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of any unspecified impurity in the portion of the Tablets taken:

Result = (r_u /r_s ) × (C_s /C _{(ERR 1-Jun-2021)} ) × 100

r_u = peak response of any unspecied impurity from the Sample solution

r_s = peak response of minoxidil from the Standard solution

C_s = concentration of USP Minoxidil RS in the Standard solution (mg/mL)

C = nominal concentration of minoxidil in the Sample solution (mg/mL)

Acceptance criteria: See Table 1. The reporting threshold is 0.1%.

Table 1

^a 2,6-Diamino-4-chloropyrimidine 1-oxide.

^b Process-related impurities that are controlled in the drug substance.

^c 6-Chloropyrimidine-2,4-diamine.

^d 6-(Piperidin-1-yl)pyrimidine-2,4-diamine.

^e Total impurities is the sum of all the impurities, including process-related impurities.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers. Store at controlled room temperature.

USP Reference Standards 〈11〉

USP Minoxidil RS