Minoxidil
(min ox' i dil).
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C9H15N5O 209.25

2,4-Pyrimidinediamine, 6-(1-piperidinyl)-, 3-oxide.
2,4-Diamino-6-piperidinopyrimidine 3-oxide [38304-91-5].
» Minoxidil contains not less than 97.0 percent and not more than 103.0 percent of C9H15N5O, calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers.
USP Reference standards 11
USP Minoxidil RS Click to View Structure
Identification, Infrared Absorption 197M Do not dry specimens.
Loss on drying 731 Dry it at 50 and at a pressure not exceeding 5 mm of mercury for 3 hours: it loses not more than 0.5% of its weight.
Residue on ignition 281: not more than 0.5%.
Chromatographic purity—
Mobile phase and Chromatographic system—Prepare as directed in the Assay.
Test solution— Prepare a solution of Minoxidil in Mobile phase having a concentration of about 0.25 mg per mL.
Procedure— Inject about 10 µL of Test solution into the chromatograph, record the chromatogram, and measure the peak response for each component. Calculate the total percentage of impurities taken by the formula:
100S / (S + A)
in which S is the sum of the areas of the minor component peaks detected, and A is the area of the major component. The total of any impurities detected is not more than 1.5%.
Assay—
Mobile phase— Prepare a solution consisting of a mixture of methanol, water, and glacial acetic acid (700:300:10), add 3.0 g of docusate sodium per L of solution, and mix. Adjust with perchloric acid to a pH of 3.0, filter, and degas.
Internal standard solution— Prepare a solution of medroxyprogesterone acetate in Mobile phase having a concentration of about 0.2 mg per mL.
Standard preparation— Dissolve an accurately weighed quantity of USP Minoxidil RS in Internal standard solution to obtain a solution having a known concentration of about 0.25 mg per mL.
Assay preparation— Transfer about 5 mg of Minoxidil, accurately weighed, to a container, add 20.0 mL of Internal standard solution, and mix.
Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph not less than four replicate injections of the Standard preparation, and record the peak responses as directed under Procedure: the relative standard deviation is not more than 2.0%, and the resolution, R, between the internal standard and minoxidil is not less than 2.0.
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. The relative retention times are about 0.8 for the internal standard and 1.0 for minoxidil. Calculate the quantity, in mg, of C9H15N5O in the portion of Minoxidil taken by the formula:
20C(RU / RS)
in which C is the concentration, in mg per mL, of USP Minoxidil RS in the Standard preparation, and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Sujatha Ramakrishna, Ph.D.
Senior Scientific Liaison
1-301-816-8349
(SM22010) Monographs - Small Molecules 2
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 3931