INTRODUCTION
Minoxidil (MXD) is a potent vasodilator and oral antihypertensive agent that was discovered to induce hypertrichosis in 60-80% of patients. Exploitation of MXD’s hypertrichosis effect led to the development of a topical product, Rogaine (Johnson and Johnson, Skillman, NJ, USA). MXD is hypothesized to increase blood flow within hair follicles and promoting potassium channel flux to prolong the anagen phase.1 Currently, topical MXD is the only Food and Drug Administration (FDA) approved topical treatment for male and female androgenetic alopecia (AGA). Topical MXD delivery remains a challenge when solubility, drug partitioning, precipitation, epidermal permeation, and diffusion path between keratinocytes and hair follicles is taken into consideration.Topical MXD solutions are associated with scalp psoriasiform contact dermatitis, scalp comedones, as well as pustular and pigmented contact dermatoses, while MXD lotion has been associated with acute-arteritic anterior ischemic optic neuropathy, Rabbit syndrome, leucoderma, and hypertrichosis.2 The development of foam formulations reduced irritation and promoted compliance. Innovations such as foams containing lecithin micro particles may further reduce residue associated with topical MXD formulations.3 This review will discuss major primary studies regarding the use of topical MXD for hair loss treatment.
MATERIALS AND METHODS
A primary literature search was conducted with PubMed/MEDLINE using the search term [topical minoxidil]. Initially, 563 articles from the years 1981 to 2017 were identified. Using the PRISMA methodology, inclusion criteria was applied: randomized controlled trials using topical minoxidil on human subjects for hair regrowth and written in English. Articles without a clinical focus on human hair loss were excluded. Finally, 23 randomized controlled trials (Oxford Centre for Evidence-based Medicine 2011 Level of Evidence I) were included in this systematic review, as depicted in Figure 1.
RESULTS
The Use of Topical Minoxidil in Androgenetic AlopeciaTopical MXD has been the first-line therapy for patients suffering from androgenetic alopecia (AGA) since 1988.4 The majority of patients using MXD also identify positive psychological benefits associated with hair loss treatment. Various MXD concentrations have been utilized for the treatment of male AGA ranging from 0.01% to 5%. Olsen et. al’s dose-dependent study using 58 males demonstrates that twice daily applications of 0.01% or 0.1% MXD solutions does not elicit any clinically significant results compared to placebo according to patient self-evaluation.5 However, 0.1% MXD solution is identified as the lowest efficacious dose to stimulate measurable hair growth after six months of application.5 Twice daily application
