A randomized controlled trial evaluating the additional effect of topical coal tar to a topical corticosteroid regimen in patients aged >16 years of age with moderate-severe atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disease, often requiring
long-term treatment. Currently, topically applied corticosteroids are used as a
standard anti-inflammatory treatment. An alternative treatment for AD is
topical coal tar, which is known to be an effective and safe treatment for AD
for ages, and is used in our department for decennia. Based on our clinical
experience, we expect adding topical coal tar to a standard corticosteroid
regimen will decrease the severity of AD, and might shorten the duration of
treatment. The additional effect of coal tar to a corticosteroid regimen has
not been reported to date.

To evaluate the additional effect of coal tar treatment to a corticosteroid
regimen in adults (aged >16 years of age) with moderate to severe atopic
dermatitis, based on the percentage change in Eczema Area and Severity Index
(EASI) at week 2. Secondary outcomes: percentage change in EASI at week 4, the
proportion of patients with EASI-75 at week 2 and week 4, decrease in NRS score
for pruritus, changes in patient-reported outcome (POEM and Patient PGA),
changes in quality of life (DLQI), and tolerability of both treatments. In
addition, we aim to investigate a possible association between a filaggrin
(FLG) genotype and efficacy of topical coal tar and/or topical corticosteroids,
and to evaluate changes in Natural Moisturizing Factor (NMF) levels in the
stratum corneum and the skin microbiota between patients treated with topical
coal tar and/or topical corticosteroids.

We aim to conduct a investigator-initiated, parallel group, randomized
controlled trial evaluating the efficacy of additional coal tar treatment to a
corticosteroid treatment regimen in patients >16 years of age with
moderate-severe AD.

Patients will be randomized in two groups: (1) topical treatment with coal tar
and a potent corticosteroid (class III) or (2) topical treatment with a potent
corticosteroid (class III) for a treatment duration of 4 weeks.

Both treatments used in this trial are normally used in daily clinical
practice. The only difference between daily clinical practice and this trial,
is the randomization of the patients in two treatment arms. In addition to
daily clinical practice, the participants are asked to fill out questionnaires,
which will take a little extra time. In addition, saliva will be collected for
DNA isolation, dead cornified cells will be collected for NMF analysis by
application of adhesive tapes, and swaps will be taken from the skin for
microbiome analysis. These are all non-invasive procedures. Therefore, we
expect the risk for participants to be negligible.