Doxepin affects acetylcholine induced cutaneous reactions in atopic eczema

Atopic eczema (AE) is a chronic inflammatory skin disease with strong itching as the prominent symptom. The pathology of itch is still in discussion, but acetylcholine (ACH) seems to be a relevant pruritogenic mediator in AE. Since efficient benefit on pruritus and excoriations has been demonstrated with tricyclic agents, we investigated how the topical treatment with doxepin (5%, Boehringer Standard, Mannheim, Germany), a tricyclic compound with anticholinergic properties, may influence ACH induced itch and cutaneous sensations (erythema, wheal, axonreflex flare).

Eleven patients with AE were included in this double blind study. For 3 days we applied doxepin cream to a defined area on the volar forearm and basic ointment to the other side 4 times daily. On day 4, ACH and sodium chloride were i.c. injected into the pretreated arms. Vasoreactions and cutaneous sensations were measured similar to studies described in previous publications from our group.

Doxepin treatment over 3 days reduced ACH provoked flare size more than 53% (P<0.005) and wheal size about 48% (P<0.005) whereas the maximal antipruritic effect was similiar to the basic therapy. The itch intensity, which is expressed as the mean AUC value, was rated at 6.12 arbitrary units after the neutral cream application and 5.9 arbitrary units after doxepin.

The clinical and experimental effectiveness of doxepin as an antipruritic drug has been known for years. However, studies focusing on ACH as a pruritogenic mediator have not been performed. The duration of the doxepin application in our study seems to be appropriate since flare and wheal development were diminished. The reason why doxepin did not develop more antipruritic action compared to the vehicle cream may be due to the fact that the doxepin free cream already possessed an antipruritic action in this experimental study design. This is probably caused by rehydrating and moisturizing effects.