Androgenetic Alopecia — SCE Dermatology MCQ

Correct answer: A — Potassium channel opener causing vasodilation and prolongation of anagen phase

The correct answer is A, potassium channel opener causing vasodilation and prolongation of anagen phase. Minoxidil is a direct-acting vasodilator that opens ATP-sensitive potassium channels in vascular smooth muscle and perifollicular tissue, causing membrane hyperpolarisation and increased blood flow to hair follicles. This vasodilatory and follicular effect prolongs the anagen (growth) phase, enlarges miniaturised follicles, and promotes conversion of vellus hairs to terminal hairs, which is the basis for its licensed use in androgenetic alopecia. Unlike finasteride, minoxidil has no hormonal mechanism; its action is purely on follicular vasculature and potassium channel-mediated cellular effects, consistent with UK product licensing (Regaine) and BNF guidance. Why the other options are wrong: E. Calcineurin inhibition: this is the mechanism of topical tacrolimus and pimecrolimus, used for eczema and vitiligo, not for pattern hair loss, and has no role in minoxidil pharmacology. C. 5-alpha reductase inhibition: this describes finasteride, an oral treatment for male pattern hair loss that blocks conversion of testosterone to dihydrotestosterone; minoxidil has no effect on androgen metabolism. B. Androgen receptor blockade: this describes agents such as cyproterone acetate or spironolactone used in female pattern hair loss with hyperandrogenism, not minoxidil, which does not bind androgen receptors. D. Direct follicular stem cell stimulation: although downstream growth factor and stem cell pathways may be modulated indirectly, minoxidil's primary pharmacological action is vascular and potassium channel mediated, not direct stem cell stimulation. Key point: Minoxidil works by opening potassium channels to cause vasodilation and prolong the anagen phase, entirely independent of androgen or hormonal pathways, which distinguishes it from finasteride and antiandrogen therapies.

Reference: electronic Medicines Compendium (emc), Regaine for Men Extra Strength Scalp Solution 5% w/v SmPC, Section 5.1 Pharmacodynamic properties; BNF, Minoxidil, https://www.medicines.org.uk/emc/product/5765/smpc