INTRODUCTION
Topical corticosteroids (TCS) are a class of medications frequently used for a wide variety of dermatologic conditions. This type of medication is generally quite effective with a favorable safety profile, making them very appealing for frequent use. As there is a wide variety of TCS available for use, they tend to be classified into groups based on potency. Since its first use in 1962, a human vasoconstrictor assay has been used, and continues to be used, with various concentrations of TCS formulations to classify their potency. The vasoconstrictor assay is based on a measure of visible blanching, which has been found to correlate with clinical efficacy.1-3 Since that time, there have been other approaches that have built off of the human vasoconstrictor assay; Dumas and Scholtz's psoriasis bioassay as well as Reddy and Singh's histamine assay both came about during the 1970s as ways to assess the anti-inflammatory properties alongside the potency of TCS.4,5
In a practical sense, it has been elucidated that the potency of a topical steroid is dependent on multiple factors.6 This can include the formulation or vehicle they are dispensed as, the site of application, the presence of compromised skin, and if an occlusive dressing has been applied to the area. This is apparent by the example of an increase of in vitro release of fluocinonide and its vasoconstriction scores with increasing solubilization in a cream base.7 However, it is important to recognize that the vehicle of a TCS preparation may not be solely dependent on whichever base is most appropriate for drug solubilization. Patients themselves tend to have preferences on the vehicle of delivery they would like to use, based on comfort, appearance, and ease of use.8 Ointment vehicles, for example, tend to be greasy and sit on top of the skin which, while aiding drug absorption, can be uncomfortable for patient use or deemed unsightly by the patient. Cream vehicles, on the other hand, tend to be more favorable to patients due to their ease of use and enhanced cosmetic appeal. However, being less occlusive may reduce drug penetration through skin.
The downside of the modern TCS potency classification is that there is no universally accepted system, and many countries have their own independent sorting arrangement of TCS. Ultimately, there are many different classifications of TCS based on whichever country a clinician may find themselves practicing in. This may result in confusion as these classification systems are not quite consistent, some are more detailed and relevant clinically than others. Furthermore, the ranking of TCS themselves is not kept consistent between varying classifications, as a steroid may be classified as mildly potent in the US system and moderately potent in the European system, which undoubtedly can cause uncertainty in choosing a product.9
In a practical sense, it has been elucidated that the potency of a topical steroid is dependent on multiple factors.6 This can include the formulation or vehicle they are dispensed as, the site of application, the presence of compromised skin, and if an occlusive dressing has been applied to the area. This is apparent by the example of an increase of in vitro release of fluocinonide and its vasoconstriction scores with increasing solubilization in a cream base.7 However, it is important to recognize that the vehicle of a TCS preparation may not be solely dependent on whichever base is most appropriate for drug solubilization. Patients themselves tend to have preferences on the vehicle of delivery they would like to use, based on comfort, appearance, and ease of use.8 Ointment vehicles, for example, tend to be greasy and sit on top of the skin which, while aiding drug absorption, can be uncomfortable for patient use or deemed unsightly by the patient. Cream vehicles, on the other hand, tend to be more favorable to patients due to their ease of use and enhanced cosmetic appeal. However, being less occlusive may reduce drug penetration through skin.
The downside of the modern TCS potency classification is that there is no universally accepted system, and many countries have their own independent sorting arrangement of TCS. Ultimately, there are many different classifications of TCS based on whichever country a clinician may find themselves practicing in. This may result in confusion as these classification systems are not quite consistent, some are more detailed and relevant clinically than others. Furthermore, the ranking of TCS themselves is not kept consistent between varying classifications, as a steroid may be classified as mildly potent in the US system and moderately potent in the European system, which undoubtedly can cause uncertainty in choosing a product.9
