Systemic injections of TTX diminished pain behaviour in a dose-dependent manner in models of inflammatory, visceral and neuropathic pain without causing adverse events, whereas morphine analgesia was associated with heavy sedation. TTX is a very promising substance for the treatment of various types of pain but needs further evaluation.

Cancer pain is a serious public health issue and more effective treatments are needed. This study evaluates the analgesic activity of tetrodotoxin, a highly selective sodium channel blocker. This randomized, placebo-controlled, parallel design study of subcutaneous tetrodotoxin, in patients with moderate or severe unrelieved cancer pain persisting despite best available treatment, involved 22 centers across Canada. The design called for tetrodotoxin administered subcutaneously over Days 1-4 with a period of observation to Day 15 or longer. All patients could enroll into an open-label extension efficacy and safety trial. The primary endpoint was the proportion of analgesic responders in each treatment arm. Eighty-two patients were randomized, and results on 77 were available for analysis. There was a nonstatistically significant trend toward more responders in the active treatment arm based on the primary endpoint (pain intensity difference). However, analysis of secondary endpoints, and an exploratory post hoc analysis, suggested there may be a robust analgesic effect if a composite endpoint is used, including either fall in pain level, or fall in opioid dose, plus improvement in quality of life. Most patients described transient perioral tingling or other mild sensory phenomena within about an hour of each treatment. Nausea and other toxicities were generally mild, but one patient experienced a serious, adverse event, truncal and gait ataxia. This trial suggests tetrodotoxin may potentially relieve moderate to severe, treatment-resistant cancer pain in a large proportion of patients, and often for prolonged periods following treatment, but further study is warranted using a composite primary endpoint.

Cancer pain is a prevalent and serious public health issue, and more effective treatments are needed. This study evaluates the analgesic activity of tetrodotoxin, a highly selective sodium channel blocker, in cancer pain. A Phase IIa, open-label, multicenter, dose-escalation study of intramuscular tetrodotoxin was conducted in patients with severe, unrelieved cancer pain. The study design called for six ascending dose levels of intramuscular tetrodotoxin, administered over a four-day treatment period in hospitalized patients, with six patients to be enrolled within each successive dose level. Twenty-four patients underwent 31 courses of treatment at doses ranging from 15 to 90 microg daily, administered in divided doses, over four days. Most patients described transient perioral tingling or other mild sensory phenomena within about an hour of each treatment. Nausea and other toxicities were generally mild, but two patients experienced a serious adverse event, truncal and gait ataxia, that resolved over days. Seventeen of 31 treatments resulted in clinically meaningful reductions in pain intensity, and relief of pain persisted for up to two weeks or longer. Two patients had opioids held due to narcosis concurrent with relief of pain. Somatic, visceral, or neuropathic pain could all respond, but it was not possible to predict which patients were more likely to have an analgesic effect. Tetrodotoxin was overall safe. It effectively relieved severe, treatment-resistant cancer pain in the majority of patients and often for prolonged periods after treatment. It may have a novel mechanism of analgesic effect. Further study is warranted.