Detection and characterization of functional (side-)effects of diphenhydramine in the central nervous system using a neuro-behavioral assay: proof of concept

Nearly 90% of drug candidates that enter clinical trials fail to receive approval from the U.S Food and Drug Administration. Approximately one-quarter of these failures are due to adverse effects in the CNS, most of which are caused by alterations in neural function. To address this issue, we employed a neuro-behavioral assay, originally designed for identification and characterization of the effects of general anesthetics on the neural oscillations of an endogenous brainstem nucleus in a fish model system. To establish proof of concept, we validated the applicability of this high-content in vivo assay by assessing possible neural (side-)effects of diphenhydramine, best known under its brand name Benadryl. In the neuro-behavioral assay, this antihistamine revealed a robust, reversible, dose-dependent neural effect, reflected by a pronounced drop in the oscillation frequency readout of the assay. This effect, presumably caused by use-dependent blocking of sodium channels, is consistent with secondary actions of diphenhydramine as a sedative and/or local anesthetic. The results of our study demonstrate the potential of the neuro-behavioral assay to predict functional (side-)effects of drug candidates in the central nervous system at earlier stages of drug development than possible with the currently available technologies.