Topical Phenytoin in Neuralgic Pain, Peripheral Modulation of Central Sensitization: Two Case Reports

Abstract

We herewith describe a topical formulation of phenytoin with a clear analgesic effect in localized neuropathic pain: in post herpetic neuralgia and trigeminal neuralgia. Such topical analgesic effect for phenytoin has not yet been described in literature. We have developed various topical phenytoin formulations and identified a stable cream base in which we compounded a range of concentrations of phenytoin up to 10%. We will present two cases supporting the analgesic effect of phenytoin cream in neuralgic pain, and discuss the putative mechanism of action of phenytoin as a topical analgesic. The essence of both cases is that, apparently, it is possible to down-regulate central sensitization processes via the modulation (inhibition) of peripheral input. This hypothesis was brought forward in 2013 based on neurophysiological data, and our clinical data seem to also support this important chapter in pain treatment. Thus, topical analgesia, in our case based on phenytoin, can play an important role in multimodal therapy of chronic neuropathic pain, related to central sensitization states.