Treatment of the Chronic Itch of Atopic Dermatitis Using Standard Drugs and Kampo Medicines

Atopic dermatitis is a common skin disease accompanied by intense itching. Relapsing eczema is caused by immune imbalances and skin-barrier disruption. The immunopathy and barrier dysfunction are closely related to the onset of itching and subsequent scratching, and intractable dermatitis is amplified by the itch-scratch cycle. The standard therapy for atopic dermatitis is topical corticosteroids and immunosuppressants to lessen the inflammation, along with moisturizing agents to improve the physiologic skin dysfunction. Corticosteroids are the primary treatment for the inflammation in atopic dermatitis. Some clinical trials demonstrated a tendency for the alleviation of pruritus with long-term treatment. Tacrolimus results in instant burning and itching in the short term, but they resolve a few days after the beginning of use and then are relieved. Substance P is a neuropeptide released from sensory nerve fibers and a neurotransmitter of pain and itching. Basic experimental reports indicated that the antipruritic effect of tacrolimus is probably dependent on depleting substance P, followed by transient induction. Oral administration of antihistamines and antiallergics is used as adjunctive pharmacotherapy for pruritus. It is known that second-generation antihistamines are less sedative or nonsedative drugs compared with the first generation, and the drugs have additional efficacy in blocking some chemical mediators. Japanese traditional Kampo medicines are also used for the treatment of atopic dermatitis. This paper discusses the efficacy of representative Kampo medicines in the treatment of inflammation and itching based on murine atopic dermatitis models. Information on the mechanism of action of Kampo medicines will result in more choice of pharmacotherapeutic agents for complex diseases such as atopic dermatitis.