[Preclinical safety evaluation of chloral hydrate after topical application using the example of psoriatic itch].

Background: Psoriasis is known today as a T‑cell-mediated autoimmunological systemic disease. The chronic inflammatory processes involve neuroimmunological factors that are held responsible not only for various aspects of psychiatric-neurological comorbidities but also for neurosensory problems, primarily itching. Amongst other things, the significance of GABA _A receptors are often discussed in this context. The topical use of chloral hydrate in semisolid preparations for antipruritic therapy goes back to Neisser and is currently experiencing a revival in individually manufactured formulations. However, it is currently unknown whether the unwanted side effects that are described for systemic use of chloral hydrate are also relevant for topical application.
Objectives: For lack of clinical safety data, preclinical tests for cutaneous cytotoxicity and calculations for systemic bioavailability after topical application have been performed.
Conclusion: The present data cannot fully remove safety concerns for topical application of chloral hydrate in the formulation favoured by the NRF (Neues Rezepturformularium)-the so-called 1‑2-3-cream. A twice daily use of the 1‑2-3-cream on a maximum of 10% of the body surface can be regarded as safe. For a better assessment of harmlessness, tests for cutaneous bioavailability (concentration-time profile) on human skin and clinical studies would be necessary.