Available at: https://www.aafp.org/afp/2021/0315/p337.html
To the Editor: The article by Drs. Stacey and McEleney references the traditional use of vasoconstriction assays to determine potency. These assays were originally described in 1962 and have evolved only minimally since then.1 It was hypothesized that the degree of skin blanching correlated with the degree of cutaneous absorption of topical corticosteroids and clinical effectiveness. Although advances in quantification have been developed, vasoconstriction still determines the potency of topical corticosteroids.2
However, the vasoconstriction assay lacks standardization and is limited in its ability to correlate potency to clinical effectiveness. The mechanisms of action of topical corticosteroids are hypothesized to be multifactorial, including antiproliferation, antipruritic, immunomodulation, and vasoconstriction. Vasoconstriction assays may not be the ideal measurement of potency and clinical effectiveness.3–5
Data on vasoconstriction assays of the skin of people of color are extremely limited, and most studies measuring the effects of medications on the skin are predominately in White patients.1,6 Aging affects skin characteristics, including thinning of the epidermis and decreased vascularity of the dermis. Although older adults have not traditionally been included in vasoconstriction assay studies, physiologically, changes attributed to aging are likely to affect these assays and may alter the pharmacokinetics of topical corticosteroids in older adults. This variable is not accounted for in the current classification of the potency of topical steroids.
In Reply: Thank you for highlighting these significant limitations of the vasoconstriction assay. Some studies support ordering the clinical potency of topical corticosteroids as determined by the vasoconstriction assay.1–4 Current practice is to prescribe topical corticosteroids according to potency charts, which were created using data gathered from their performance on the vasoconstriction assay. No alternative model has been widely adopted as an acceptable replacement.