Use of Minoxidil Sulfate versus Minoxidil Base in Androgenetic Alopecia Treatment: Friend or Foe?

In Brazil, alternatively, there has been a rise in the prescription and use of MXS-based formulations due to its pharmaceutical solubility [6, 7]. However, in addition to the issue of its higher molecular weight, MXS is naturally unstable in aqueous solution, negatively affecting its bioavailability to the hair follicle and increasing its irritation potential to the scalp. Therefore, efficacy of MXS compared to MX base for the treatment of AGA may be impaired, and the same efficacy may not be expected as in the original clinical trials with MX base. The MX sulfotransferase activity is not the same in every individual. MXS represents an alternative with advantage over MX in individuals with low MX sulfotransferase activity, since the demonstration of an association between MX response and the degree of MX sulfatation [8]. However, in order to compensate such decreased response, MXS would have to be used at higher concentrations (10–15%) due to its decreased capacity of transcutaneous absorption and packaged in small volumes, because of its high degree of degradation. Indeed, a Swiss retrospective study of 44 patients with AGA (13 males with Hamilton-Norwood type AGA class III or above and 31 females with Ludwig type AGA I–III) unresponsive to a minimum of 6 months of 5% MX solution b.i.d. showed increase in hair growth in 97.7% using a 10% MXS solution once daily during a mean treatment period of 4.09 months. The treatment was well tolerated by patients, among whom 6.8% suffered from irritation, erythema, and folliculitis of the scalp. No major adverse effect was noted [9]. We aim to emphasize the differences between topical formulations of MX and MXS available on the Brazilian market, i.e., penetration and stability issues for MXS formulations, and the problem of low sulfotransferase activity for MX prescriptions. Our opinion is that topical MX base remains the first-line topical agent for treatment of male and female AGA, unless the patient proves to be unresponsive, then a formulation of MXS at probably higher concentrations may present an alternative with enhanced efficacy. For this purpose, a novel enzymatic assay may predict MX response [10]. Comparative clinical trials and pharmacological studies with different formulations, either ready for use or custom made, with MX base or MXS, should be conducted in order to make final recommendations for optimal use in AGA treatment.