Misoprostol in Refractory Neuralgic Pain: From Clinical Neurology to an EP-Receptor Hypothesis of Pharmacodynamic Persistence.

This hypothesis originated from the first author's personal experience in adult neurology, in which selected refractory cranial or postherpetic neuralgias occasionally appeared to improve rapidly after off-label misoprostol. The original records are unavailable; these physician recollections are not efficacy data and serve only as the hypothesis generator. Independent published precedents are limited to small uncontrolled reports in multiple-sclerosis-associated trigeminal neuralgia. A further recollection was that perceived benefit often waned after several weeks at conventional daily exposure, whereas lower or intermittent exposure sometimes appeared to remain useful for longer; this observation is likewise unverifiable and does not define a therapeutic dose. Misoprostol is rapidly converted to misoprostol acid (plasma half-life of 20-40 min). We ask whether a brief, reversible exposure could produce pharmacodynamic persistence, defined here as a reproducible pain-relevant effect that outlasts measurable drug exposure, through EP-receptor trafficking, compartmentalized GPCR signaling, or downstream cellular changes. The model also predicts that the concentration-response relationship may be non-monotonic: increasing or repeated exposure could attenuate or reverse a favorable effect by recruiting opposing EP pathways or adaptive receptor/cellular responses. No direct evidence shows that misoprostol produces such persistence in neural tissue, and PGE2/EP signaling can also be pronociceptive. Receptor-resolved concentration-response and pulse-washout experiments must therefore separately demonstrate receptor signaling, persistent cellular change, altered neuronal excitability, and ultimately blinded analgesic benefit. Neuropathic corneal pain is considered only a secondary mechanistic model. No evidence-based dose can currently be recommended.