Are wash outs needed in clinical trials of topical agents?

The Journal of Dermatological Treatment attracts reports of many clinical trials. Well-designed clinical trials often include a ‘wash out' period, a requirement that patients discontinue their previous treatment for a period of time before they begin the study treatments. For example, psoriasis or atopic dermatitis studies might include a wash out of 1 or 2 weeks for topical treatments, a month for phototherapy or oral agents, or even longer wash out periods if the patient has been on a biologic medication.

We like to think that these wash out periods are not necessary, particularly for topical treatments. When developing an investigator-initiated clinical trial, we try not to include a wash out period. One reason to not include a wash out period is that in clinical practice, we do not require patients to wait weeks or months after stopping a treatment to start a new treatment. On the contrary, we might even overlap a new treatment with an existing treatment in order to get control of the disease before recommending them to stop their earlier treatment. Studies that do not have wash out periods will, therefore, be more informative about what to expect in clinical practice.

But we have a strong aversion to wash out periods for topical treatments, because we believe that patients probably are not taking the previously recommended topical treatment anyway. Consider atopic dermatitis, for example. If we take a patient with total body, severe, lichenified atopic dermatitis, resistant to all topical and systemic treatment, admit them to the hospital and treat them with topical triamcinolone, they clear up in just 2–3 days. If a patient considering entering a trial is not getting better with the previously recommended topical treatment, it is likely that they are not using it. Objective studies of patients' adherence to topical treatment confirm very poor use of topical medications, especially in the treatment of chronic skin diseases such as psoriasis, in which reported adherence rates are between 22 and 67% (1).

If patients are not clearing up, it is likely they are not using the topical treatment. And if they are already off the treatment to the point it is not working, then requiring a wash out period just seems like unnecessary overkill, a needless barrier to study recruitment, on top of being inconsistent with how medical care is actually practiced in the clinic setting. While we expect that trials for registration will continue to include wash outs for most trials, we will look on them in a bemused way.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.