Do Second-Time Users of Topical Imiquimod have a More Rapid Onset of Clinical Response?

Introduction: Topical imiquimod is commonly used in dermatology for treatment of actinic keratoses (AK). Prior studies in humans and mice have suggested the potential for immune recall with imiquimod based on higher degrees of AK clearance and activation of memory γδ T-cells in a mouse model. Anecdotal reports suggest a more rapid time-to-onset of clinical response with second time use of imiquimod. However, the potential for immune recall demonstrated by time-to-onset of clinical response has not been formally investigated. Objective:  The primary objective of this study was to determine if there is a difference in time-to-onset of clinical response between naive and prior users of topical imiquimod for the treatment of actinic keratoses. Methods: A total of 92 patients were treated with 5% imiquimod cream for actinic keratoses of the head and neck. Patients were instructed to apply 5% imiquimod cream to the affected areas once daily until reaching a therapeutic endpoint of crusting/scabbing. The primary endpoints in the study were time (days) to onset of erythema and time to onset of crusting/scabbing. Results were self-reported. Results:  The average time (days) to onset of erythema was 5.48 ± 3.19 days in naive users and 4.7 ± 2.91 days in prior users (p= 0.22). Average time to onset of crusting/scabbing was 9.2 ± 4.34 days in naive users and 9.02 ± 3.65 days in prior users (p=0.35). Conclusion: Our study revealed there is no difference in time-to-onset of erythema or scabbing/crusting with second-time use of imiquimod.  While immune recall may be possible with use of imiquimod, the results of this study indicate that it may be independent of time-to-onset of clinical response.