opINIoN | BALDNESS | accounts for approximately 15% of all
hairs at any one time. Strictly speaking there is a fourth phase
of hair growth — exogen. This occurs after telogen, and is the normal process by which hair is shed.
Treatment Current pharmacological treatment options for male pattern baldness are largely based on an understanding of the pathogenesis of the condition. It appears that normal, large, pigmented, terminal hairs are replaced by fine, colourless hairs known as vellus hairs (the type of fine hair normally found in places like the face and the trunk). This seems to be related to the fact that the anagen phase is shorter than usual, so normal hair has less time to grow. The duration of anagen is under the
itself absorbed into Pfizer in 2002) developed a topical formulation for the treatment of male pattern baldness. Topical minoxidil was initially sold as a prescription drug under a number of brand names, such as Regaine, Rogaine and Minoxigaine, but was subsequently sold as an over‑the‑counter product. In 2006, Pfizer sold the rights to minoxidil to McNeil PPC, part of Johnson & Johnson. J&J does not release sales figures for the product. The mechanism by which minoxidil
the hair shaft grows
at a rate of approximately 1 cm per month, and each hair can last for up to 8years.
effect.
control of androgens, and male pattern baldness is associated with a greater than normal sensitivity to androgens. However, it is not testosterone but its metabolite, 5‑dihydrotestosterone (DHT), that appears to be the causative agent. The enzyme responsible for the conversion of testosterone to DHT in the skin is the steroid 5α‑reductase. The evidence for a causative role for
DHT includes: ■ That men with a genetic deficiency of 5α‑reductase do not develop male pattern baldness, despite normal testosterone levels ■ The demonstration of higher levels of 5α‑reductase and DHT in the scalp of balding men compared with normal men ■ That inhibitors of 5α‑reductase are among the most effective agents for the treatment of male pattern baldness.
However, the exact mechanism by
which DHT causes baldness remains unclear. The first pharmaceutical product to be
70 ❚
approved for treating hair loss was minoxidil, which was originally developed by the Upjohn Company in the 1970s for the treatment of hypertension. It was noted in clinical use that many patients developed excessive hair growth while being treated with minoxidil, and Upjohn (which later became a part of Pharmacia,
May 2011 |
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promotes hair growth is still uncertain, although a number of theories have been proposed. Initially it was suggested that it was related to the drug’s vasodilatory properties, the same mechanism that underlies
its Diazoxide,
ant ihyper tens ive another
antihypertensive drug with a similar mechanism to minoxidil, has also been reported to increase hair growth, and studies using laser Doppler velocimetry (LDV) have shown an increase in blood flow in the skin after topical application of minoxidil. Other possible explanations are that
minoxidil promotes cell proliferation and DNA synthesis; that it has an anti‑androgenic effect; or even that it has an immune suppressive effect and inhibits the activity of T‑lymphocytes. It is also worth noting that the precise formulation of minoxidil used can affect its efficacy — lotions containing 5% minoxidil seem to be more effective that the 2% solutions used in the past, and a 5% foam formulation has also found wide acceptance. Today the product is used as an adjunct to hair transplantation as well as on its own. Topical minoxidil has a number of
drawbacks, the chief of which is that hair growth ceases when the treatment is stopped. Like all topically applied medications, it can cause skin irritation and it has been reported that alcohol in the formulation can cause dryness of the scalp, which may lead to dandruff. In addition, there have been reports of systemic absorption of minoxidil causing hypertrichosis (excessive hair growth) at other sites on the body. The second drug to come into clinical
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