Source: Medicines Authority (MT) Revision Year: 2023 Publisher: Laboratoires Bailleul S.A., 10-12 Avenue Pasteur, L-2310 Luxembourg – Luxembourg
Pharmacotherapeutic group: Other dermatologicals
ATC Code: D11AX01
After topical use, minoxidil demonstrated to stimulate hair growth in patients with androgenic alopecia; however, the mechanism of action of minoxidil is unknown.
The hair loss stabilization is observed in every 4 of 5 patients. Hair growth is subjected to a certain individual variability. However, it may be observed after 4 or more months with regular use of cutaneous solution containing minoxidil. Minoxidil topical application has not shown any systemic effects on the drug absorption when analyzed in controlled studies in normotensive patients or with untreated hypertension.
After topical application, the absorption of minoxidil from normal intact skin is low; in average, only 1.7% (from 0.3–4.5%) of the total applied dose is systemically absorbed. In contrast, after oral administration of minoxidil tablets, the drug is mostly absorbed from the GI tract. Once the topical application of minoxidil is discontinued, approximately 95% of systematically absorbed minoxidil is eliminated in the following 4 days. The effects of concomitant skin diseases in the absorption of topically applied minoxidil are unknown.
The biotransformation of the absorbed minoxidil after topical application was not completely determined. Oral administrated minoxidil is mainly metabolized by the combination with glucuronic acid in N-oxide position of the pyrimidine ring, but the conversion to more polar metabolites is also observed. The known metabolites have a lower pharmacological effect when compared with minoxidil. Minoxidil does not bind to plasma proteins and its renal clearance corresponds to the glomerular filtration rate. Minoxidil does not cross the blood brain barrier.
Minoxidil and its metabolites are dialyzable; its elimination is mainly urinary.
Studies in animals have shown risks of adverse effects on fertility and embryo-fetal development only with excessive exposure levels, if compared to those observed in clinical use.
Minoxidil has not shown genotoxic potential. In carcinogenicity studies conducted in rats and mice, the topical administration of minoxidil resulted in increased incidence of hormone-mediated tumors. This tumorigenic/carcinogenic activity is considered to be secondary to hyperprolactinemia, which occurs only with high absorption levels on rodents, and it will not represent a risk to clinical use.
In pre-clinical studies of local tolerance potential primary skin irritations were not observed. Minoxidil has not induced sensitisation by skin contact or IgE-mediated sensitisation and it has not phototoxic or caused photoallergic reactions.
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