Minoxidil (C₉H₁₅N₅O)
Description
Minoxidil (C₉H₁₅N₅O) is a vasodilatory compound originally developed as an oral antihypertensive drug in the 1960s. Its hair growth-promoting effects were discovered as a side effect, leading to FDA approval in 1988 (2% solution) and 1998 (5% solution) for treating androgenetic alopecia (AGA) and alopecia areata (AA).
Chemical Properties:
Molecular Weight: 209.25 g/mol
Advanced Physicochemical Data:
|
Property |
Specification |
|
Melting Point |
248-250°C (with decomposition) |
|
pKa Values |
4.6 (pyrimidine N-oxide), 7.9 (piperidine N) |
|
LogP (Octanol/Water) |
1.1 ± 0.1 |
|
Crystal Form |
Monoclinic, space group P2₁/c |
Solubility Profile:
|
Solvent |
Solubility (mg/mL, 25°C) |
Notes |
|
Water |
2.2 |
pH-dependent |
|
Ethanol |
>50 |
Preferred solvent |
|
Propylene Glycol |
30-40 |
Common vehicle |
|
Glycerin |
5-10 |
Limited solubility |
|
Isopropyl Myristate |
<1 |
Poor solubility |
Manufacturing Process
Synthesis:
Starting material: 2,4-diamino-6-chloropyrimidine
Key steps: N-oxidation, piperidine substitution
Yield: 75-80% (after purification)
Purification:
Recrystallization from ethanol/water
Charcoal treatment for decolorization
Final purity: ≥99.5%
Formulation Types:
Topical Solutions (Liquid/Foam):
5% for men, 2% for women (FDA-approved).
Foam variant reduces scalp irritation (propylene glycol-free).
Oral Minoxidil (Off-label):
Low-dose (0.25–5 mg/day) used for systemic absorption.
Quality Specifications
|
Parameter |
Requirement |
Test Method |
|
Assay |
95.0-105.0% |
HPLC |
|
Related Substances |
≤1.0% |
HPLC |
|
Heavy Metals |
≤10 ppm |
ICP-MS |
|
Microbial Limits |
<100 CFU/g |
USP <61> |
|
Residual Solvents |
Meet ICH Q3C |
GC |
Benefits
✔ Stimulates Hair Regrowth – Revives dormant follicles
✔ Slows Hair Loss – Extends anagen phase
✔ Safe for Long-Term Use – Minimal systemic absorption
✔ Non-Hormonal – Does not affect DHT levels
Applications
AGA Treatment: Daily topical application (men: 5%, women: 2%)
Post-Chemotherapy Recovery: Reduces treatment-induced hair loss
Combination Therapy: Paired with finasteride for enhanced efficacy
Cosmetic Hair Serums: Incorporated into scalp-stimulating formulations
Product Processing
