Minoxidil (also called 2,4-pyrimidinediamine, 6-(1-piperidinyl)-, 3-oxide) is used since 1987 as a topical agent for the treatment of androgenic alopecia. Minoxidil was first designed, in the 1970s, as a potent peripheral vasodilator agent for the treatment of severe refractory hypertension. Regarding its serious side effects, oral minoxidil has been reserved only for cases of severe hypertension which are reluctant to maximum doses of three antihypertensive agents, including a diuretic.
Since about one-fifth of patients under oral minoxidil treatment developed hypertrichosis, a topical form was developed for the treatment of androgenic alopecia, initially for males and subsequently also for females. This topic will deal only with topical minoxidil since it is the most commonly used form of the molecule.
Two forms of topical minoxidil are available: a solution (liquid form) and a foam. The solution contains alcohol and propylene glycol which are two molecules necessary to solve 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 age 18 (the use of minoxidil in children is off-label). Long-term use of minoxidil is recommended to maintain the clinical results, as these effects regress with the drug discontinuation.
Current uses of topical minoxidil include:
Topical minoxidil (empirical formula C9H15N5O) is a hair growth stimulator. Its mechanism of action is not exactly established. Scalp sulfotransferase changes minoxidil into minoxidil sulfate, which is thought to be the active form of the molecule. Variations between individuals in sulfotransferase activity may be an explanation of interindividual variations in minoxidil efficiency.
Minoxidil acts by shortening telogen phase and thus causing the quiescent hair follicles to enter prematurely into anagen phase. The shortening of telogen phase may induce an important telogen effluvium after the initiation of minoxidil therapy. In the other hand, minoxidil induces an extension of the duration of anagen phase. Increased hair length and diameter is a clinical effect of minoxidil.
The effect of minoxidil occurs after approximately 8 weeks of treatment, and it is maximal after 4 months.
Minoxidil is thought to intervene on the potassium channels of the vascular smooth muscles and hair follicles, which may induce the following effects:
Minoxidil may have antifibrotic properties since it can affect collagen synthesis.
Minoxidil is available in the United States as an over-the-counter topical agent. It is used twice daily (1 ml dosage each). No scalp massage is needed after use. Minoxidil uptake is about 50% after an hour and 75% after 4 hours. Some practitioners associate microneedling with topical minoxidil to enhance its efficiency, but more studies are needed to assess the value of such an association.
Oral minoxidil is not FDA-approved for hair loss even though some clinical trials have used it at various doses (0.25 to 2.5 mg daily).
Studies have shown that 5% minoxidil was more effective than 2% minoxidil in the treatment of alopecia. Clinical response to minoxidil is more pronounced if alopecia evolves since less than 5 years (mainly in young adults), and the hair follicles are not deeply miniaturized.
Minoxidil is well tolerated. However, propylene glycol contained in the liquid form (solution) of minoxidil may be the cause of some adverse effects reported by patients:
Minoxidil and propylene glycol are the major allergens in allergic contact dermatitis. Patch testing may be helpful to reveal the causative agent. In case of allergic contact dermatitis to propylene glycol, minoxidil foam (i.e., not containing propylene glycol) may be used.
Minoxidil is contraindicated in patients who have a history of hypersensitivity to the drug or its components (such as propylene glycol).
The use of minoxidil is not advised in pregnant and breastfeeding women. Even though minoxidil is not known to be teratogenic, rare cases of congenital disabilities have been reported.
Patients using topical minoxidil should be regularly monitored for scalp changes and localized/generalized hypertrichosis. Hypotension is exceptionally reported in patients using topical minoxidil.
Percutaneous toxicity is exceptional after a conventional use of minoxidil. There is no known antidote for minoxidil massive oral ingestion. Accidental oral ingestion of minoxidil results usually in mild effects, mainly vomiting and does rarely require hospitalization. However, cases of hypotension, tachycardia, and/or electrocardiographic changes after accidental ingestion have been reported. Refractory hypotension may be managed by intravenous fluids and vasopressor agents. Gastric wash and activated charcoal may be indicated to prevent systemic toxicity in massive accidental ingestion of minoxidil.
Male pattern baldness has no cure and the drug industry often hypes up new drugs. Minoxidil has been around for 3 decades and is widely prescribed by nurse practitioners, primary care providers and dermatologists. Unfortunately, minoxidil is not an effective drug for hair growth; it is not reliable or consistent in its effectiveness. Most men see no difference compared to a placebo. Healthcare workers should educate patients that there is no good agent for hair growth and most products on the market are shams and scams- minoxidil falls somewhere in the middle. It is a porhibitively expensive drug which does not work for hair growth.
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