Topical Minoxidil

Summary

Synopsis

When minoxidil is administered orally for periods in excess of 1 month, hypertrichosis occurs as a side effect in a majority of patients. Consequently, topical minoxidil¹ has been developed to try to improve hair growth in patients with alopecia areata and alopecia androgenetica.

Preliminary studies have shown that topical minoxidil promotes cosmetically acceptable hair regrowth in a variable proportion of patients with alopecia areata. Data from a large multicentre trial indicate that cosmetically worthwhile results are achieved in about one-third of subjects with alopecia androgenetica after 1 year of treatment A much higher proportion (about 80%) of patients with alopecia androgenetica exhibited some non-vellus hair regrowth after 1 year, and whether more of these patients would develop a cosmetically acceptable result with a longer treatment period is an important area of future investigation. Initial indications suggest that less severe disease is a predictor of likely response.

Thus, topical minoxidil would seem to be a useful treatment modality for patients with alopecia androgenetica — a disease for which no other safe and effective drug therapy exists. Results from treating patients with alopecia areata with topical minoxidil, although encouraging, have been more variable and require further evaluation. Even though a number of questions remain to be answered about topical minoxidil (as would be expected at this stage in its development), it would seem to be the first available drug with the potential to promote substantial hair regrowth in these divergent diseases.

Pharmacodynamic Properties

Preliminary studies in patients with alopecia areata suggest that topical minoxidil 1% lotion promotes a return to normal hair follicle diameter and depth, a marked decrease in perifollicular infiltrate, and an opening up of previously closed dermal blood vessels. Morphological changes in patients with alopecia androgenetica treated with topical minoxidil would seem to support the view that it increases hair growth via induction of hypertrophy in pre-existent small follicles. A number of modes of action have been postulated and direct stimulation of the hair follicle epithelium seems the most probable. However, further research is essential to fully define the mechanisms involved.

Pharmacokinetic Studies

Preliminary investigation of the pharmacokinetic properties of minoxidil following topical application of 1% or 5% lotions (the commercially available preparation is a 2% lotion) revealed a low level of percutaneous absorption with serum concentrations very rarely exceeding 5 µg/L. After single application, or following 9 days’ treatment with minoxidil lotion 1% or 5%, less than 5% of the administered dose was recovered in the urine and none was found in the faeces.

Therapeutic Trials

In patients with alopecia areata, topical minoxidil 1% to 5% in a variety of formulations usually produced significantly better regrowth of hair than placebo. Although regrowth of vellus, intermediate, and terminal hair has been observed, the number of patients achieving a cosmetically acceptable response was variable (up to about 50%). In one study, topical minoxidil 5% lotion applied twice daily increased the response rate and the quality of hair growth compared with previous experience with a 1% lotion.

In a dose-response study involving 89 subjects with male-pattern baldness, topical minoxidil 1% lotion appeared to be the lowest effective concentration and slightly more impressive results were produced by a 2% lotion. A multicentre trial involving approximately 2000 subjects with male-pattern baldness reported that topical minoxidil 2% or 3% lotion applied twice daily for 1 year produced cosmetically acceptable hair regrowth in about one-third of those treated. Additionally, a much higher proportion (almost 80%) showed some non-vellus hair regrowth at the time of assessment. The 2% lotion was considered to offer the better benefit-to-risk ratio.

For patients with alopecia areata and alopecia androgenetica the initial indications are that less severe disease, as indicated by smaller bald area, a greater number of intermediate hairs and a shorter duration of disease, may be a good predictor of likely response.

Side Effects

Topical minoxidil has been well tolerated in the majority of patients. Dermatological reactions such as itching, scaling, flushing and rarely allergic contact dermatitis have been the only adverse experiences to be reported in clinical trials which are possibly or probably drug related. Isolated reductions of blood pressure and increases in heart rate have been observed but they would not seem to be a problem for most patients.

Administration

Experience from therapeutic trials indicates that topical minoxidil should be applied twice daily. Continued therapy appears to be necessary to maintain hair growth. The drug should be used cautiously, if at all, in patients with underlying hypertension or other cardiovascular disease.