Study Classifies 232 Topical Corticosteroid Formulations

Alexa C. Bowie, MPH

A new classification study classified 232 topical corticosteroids (TCS) formulations into 3 distinct potency classifications, which investigators involved in the study felt could be used to avoid limitations in comparisons, robust exposure classification, and clinical interpretations.

Topical corticosteroids are frequently prescribed when treating inflammatory skin diseases, and are available in a variety of formulations and potency levels.

But previous research has suggested that increasing the potency, application frequency, and duration of TCS could lead to extracutaneous adverse events such as adrenal suppression, diabetes, osteoporosis, and osteoporotic fractures.

Additionally, TCS potency classification systems are known to vary, and an individual investigator’s choice of classification system could influence study results and interpretation.

As such, an investigative team led by Alexa C. Bowie, MPH, of the Women’s College Hospital of Toronto, set out to classify TCS formulations using 3 commonly used systems while also assessing their agreement and correlation.

The team utilized the Ontario Drug Benefit Formulary, the Anatomical Therapeutic Classification (ATC) of the World Health Organization, a recent Cochrane review, and various published sources to amass a list of unique TCS formulations from August 11, 2021, to January 6, 2022.

Unique formulations were determined by the combination of corticosteroid molecule, concentration, and vehicle.

Bowie and colleagues then developed a comprehensive classification list through combined data of various 7-category potency lists, a 4-category classification from Cochrane, and the 4-category ATC classification.

Notably, the 7-category US system featured in the study was consolidated into 4 categories.

Finally, Cohen weighted κ (κw) and Spearman rank correlation coefficients (r) were computed to examine agreement and correlation between the classification systems.

Overall, a total of 232 unique TCS formulations were identified from ATC (231), US classification (232), and the Cochrane review (89).

Investigators observed a low to moderate agreement but strong correlation between the classification systems. The US classification in particular had a weak agreement with the ATC system(κw, 0.53,95% CI, 0.45-0.60) and moderate agreement with the Cochrane review classification (κw, 0.60, 95% CI, 0.48-0.73).

Meanwhile, a weak agreement between the ATC and Cochrane review classifications (κw, 0.58; 95% CI, 0.46-0.71) was also noted.

Promisingly, the US classification strongly correlated with the ATC system (r, 0.77, 95% CI, 0.71-0.82) and Cochrane review classification (r, 0.74; 95% CI, 0.62-0.82), and a strong correlation was also observed between the Cochrane review and ATC classifications (r, 0.71, 95% CI, 0.58-0.80).

With this study, Bowie and colleagues deemed it necessary to establish “transparent classification” of TCS in the pursuit of stronger and more reliable dermatologic outcomes and treatments, and considered there list of classifications to be “comprehensive” and supportive of future pharmacoepidemiologic studies.

“Investigators need to transparently report how they categorize TCS potency and consider sensitivity analyses with alternative classifications to examine the robustness of their findings,” the team wrote.

The study, "Agreement and Correlation Between Different Topical Corticosteroid Potency Classification Systems," was published online in JAMA Dermatology.