Halneuron

Halneuron is the proprietary injectable formulation of tetrodotoxin (TTX), a naturally occurring guanidinium alkaloid neurotoxin and potent, reversible blocker of TTX-sensitive voltage-gated sodium channels (VGSCs), developed by WEX Pharmaceuticals Inc. (Vancouver, British Columbia, Canada; now Dogwood Therapeutics Inc., NASDAQ: DWTX) as a non-opioid analgesic for moderate to severe neuropathic and cancer-related pain. The active pharmaceutical ingredient, tetrodotoxin (C11H17N3O8, molecular weight 319.3 g/mol, CAS 4368-28-9), blocks TTX-sensitive sodium channel subtypes NaV1.1, NaV1.2, NaV1.3, NaV1.4, NaV1.6, and NaV1.7 at low-nanomolar concentrations, with IC50 values ranging from approximately 2.3 nM (NaV1.6) to 36 nM (NaV1.7). The NaV1.7 subtype is of particular analgesic relevance: human loss-of-function mutations in SCN9A (the gene encoding NaV1.7) produce congenital insensitivity to pain, establishing the channel as a genetically validated analgesic target. Halneuron is administered by subcutaneous injection and does not cross the blood-brain barrier in pharmacologically significant quantities, conferring a safety profile that is free of the euphoria, sedation, tolerance, addiction, and cognitive impairment associated with opioid and centrally acting analgesics.

The clinical development program has evaluated Halneuron in over 700 subjects across multiple Phase 1, Phase 2, and Phase 2b trials. The pivotal cancer pain trial (Hagen et al. 2017), a multicentre, randomized, double-blind, placebo-controlled study of 165 patients at 19 sites in Canada, Australia, and New Zealand, demonstrated a clinically significant estimated effect size of 16.2% on the pain endpoint for TTX 30 micrograms subcutaneously twice daily for four days versus placebo, with 51% of TTX-treated patients achieving 30% or greater pain reduction compared to 35% on placebo. An open-label safety and efficacy study (Hagen et al. 2011) in 77 cancer pain patients demonstrated that the analgesic effect persisted for weeks to months following a four-day treatment cycle, a finding that distinguishes TTX from conventional short-acting analgesics and suggests a disease-modifying or neuroplastic component to the mechanism. The Phase 2 dose-finding trial for chemotherapy-induced neuropathic pain (CINP; Bhatt et al. 2021) in 125 patients identified the 30 microgram twice-daily regimen as the optimal dose for further study, with cumulative responder analysis showing significant separation from placebo. The ongoing Phase 2b HALT-CINP trial, conducted at approximately 30 sites in the United States under Dogwood Therapeutics, reported positive interim results in December 2025 from 97 patients, with Halneuron-treated patients demonstrating separation from placebo on pain improvement over four weeks, a dropout rate of approximately 4.4% (substantially below rates observed with approved chronic pain agents), and encouraging safety and tolerability.

Pharmacokinetics following subcutaneous injection are characterized by rapid absorption (time to maximum plasma concentration approximately 1.5 hours), dose-proportional exposure, and an elimination half-life of approximately 4.5 hours, with plasma concentrations falling below the limit of quantification within 24 hours. The compound is not metabolized by cytochrome P450 enzymes and does not produce the pharmacogenomic variability that complicates agents dependent on CYP2D6 or CYP3A4. Safety data from Phase 1 dose-escalation studies in healthy adults (doses of 15 to 45 micrograms subcutaneously) demonstrate that Halneuron is well tolerated, produces no QT prolongation, and carries no proarrhythmic proclivity. The most common adverse events across clinical trials are perioral paresthesia, oral numbness, headache, dizziness, nausea, and myalgia, all generally mild to moderate and self-limiting.

This monograph reviews the chemistry, natural history, and pharmaceutical development of tetrodotoxin as Halneuron; the molecular pharmacology of TTX-sensitive sodium channel blockade with emphasis on NaV1.7; the human pharmacokinetic record; the preclinical analgesic evidence base in rodent models of neuropathic, inflammatory, and cancer pain; the complete clinical evidence base across cancer pain, chemotherapy-induced neuropathic pain, and ongoing Phase 2b trials; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse-event signal; and a structured comparative assessment of five alternative analgesic candidates for chemotherapy-induced neuropathic pain (duloxetine, pregabalin, vixotrigine, capsaicin 8% patch, and lidocaine 5% patch) against Halneuron on five competency standards.