The use of phosphodiesterase inhibitors for the treatment of alopecia

Background: Hair loss encompasses a group of scarring and nonscarring diseases with limited treatment options. Understanding the pathogenesis of alopecias has led to the experimental use of phosphodiesterase inhibitors (PDEi). Objective: To perform a systematic review of literature surrounding the use of PDEi for alopecia. Materials and methods: A search was conducted using PubMed in February 2019 on PDEi and alopecia. Inclusion criteria were clinical trials, prospective or retrospective studies, case series and case reports written in English, using PDEi in human subjects for the treatment of alopecia. Results: Fifteen articles were included for review - eight discussing the use of topical caffeine 0.2%-2.5% for the treatment of androgenetic alopecia (AGA) and telogen effluvium (TE), one using injectable caffeine for AGA, one using topical sildenafil for pediatric alopecia areata (AA), and five using oral apremilast for adult AA. Conclusions: Preliminary results using topical caffeine for AGA or TE are promising with minimal adverse events. However, these studies are primarily single-center trials with few patients. Studies using topical or systemic PDEi for AA demonstrate limited success. Current research using PDEi for alopecia is limited, however new clinical trials are being conducted.