The initial design of minoxidil (also called 2,4-pyrimidinediamine, 6-(1-piperidinyl)-, 3-oxide) was as a potent peripheral vasodilator agent for the treatment of severe refractory hypertension in the 1970s. Due to its serious side effects, oral minoxidil was reserved for cases of severe hypertension that were reluctant to maximum doses of three antihypertensive agents.
Additionally, about one-fifth of patients under oral minoxidil treatment developed hypertrichosis. In 1987, a topical form was developed for the treatment of androgenic alopecia, initially for males and subsequently also for females. This article focuses specifically on topical minoxidil, the most commonly used form of the molecule.
Topical minoxidil is available in two forms: a solution (liquid form) and a foam. The solution contains alcohol and propylene glycol, two molecules necessary to dissolve minoxidil and increase its uptake in the tissues. Formulations containing 2% and 5% minoxidil are generally used in scalp alopecia in patients who are over 18 years of age. Clinicians can use minoxidil in children; however, it is considered off-label use. Long-term use of minoxidil is necessary to maintain the clinical results, as these effects regress with drug discontinuation.
Current uses of topical minoxidil include:
- Androgenic alopecia (the only FDA-approved indication)
- Alopecia areata: Minoxidil has been shown to induce a positive clinical response, either used alone or combined with other medications such as corticosteroids.
- Alopecia induced by chemotherapy: Minoxidil has demonstrated minimization of hair loss and acceleration of hair regrowth.
- Hair transplant: Telogen effluvium is a frequent observation after a hair transplant. Minoxidil, when administered before and after hair transplant, minimizes hair loss. Treatment should be temporarily suspended three days before the transplant to avoid excessive bleeding.
- Scarring alopecia: Minoxidil has shown evidence to exhibit an antifibrotic action. Therefore, topical minoxidil treatment can be a therapeutic choice in the early course of dermatoses leading to scarring alopecia, such as scalp burning disease.
- Monilethrix: Minoxidil leads to synchronization of the entry of hair follicles into the anagen phase.
- Hereditary alopecia/hypotrichosis: The use of minoxidil has demonstrated to be beneficial by inducing a thickening in hair shafts.