Respiratory, neuromuscular, and cardiovascular effects of neosaxitoxin in isoflurane-anesthetized sheep.

BACKGROUND: Neosaxitoxin (NeoSTX) is a potent site-1 sodium-channel blocker being developed as a local anesthetic. Doses of 100 µg have been used by local infiltration in anesthetized adult humans without adverse effect. We hypothesized that similar doses could cause significant respiratory, neuromuscular, and cardiovascular impairment and sought to test this hypothesis in sheep. METHODS: Procedures were approved by the Institutional Animal Care and Use Committee. In neuromuscular/respiratory experiments, 33 intubated, isoflurane-anesthetized sheep were randomized to 6 NeoSTX treatment groups: saline control, 1 µg/kg subcutaneous (SC), 1 µg/kg intravenous (IV), 2 µg/kg SC, 2 µg/kg SC with bupivacaine 0.25%, and 3 µg/kg SC. Primary outcome measures were doxapram-stimulated inspired volume (DSIV) and quantitative limb acceleration. In cardiovascular experiments, 8 sheep received escalating IV doses of NeoSTX (1, 2, and 3 µg), with hemodynamic and electrocardiographic measurements. Data were analyzed using repeated-measures analysis of variance with post hoc Bonferroni-corrected comparisons. RESULTS: NeoSTX 1 µg/kg IV and SC produced no significant reduction in DSIV or limb acceleration compared with baseline. NeoSTX 2 µg/kg SC produced clinically mild reduction in twitch and DSIV; animals recovered well postoperatively. Coadministration of bupivacaine did not worsen these effects. NeoSTX 3 µg/kg produced severe and prolonged impairment of DSIV and limb acceleration. Escalating IV doses of NeoSTX produced mild decrements in heart rate, systemic arterial pressure, and systemic vascular resistance; cardiac output was maintained. Transient interventricular conduction delay occurred without cardiac arrest or ventricular ectopy. CONCLUSIONS: In our sheep model, neuromuscular, respiratory, and cardiovascular effects of NeoSTX were dose dependent and mild using the dose range anticipated for clinical use.

Comparison of neosaxitoxin versus bupivacaine via port infiltration for postoperative analgesia following laparoscopic cholecystectomy: a randomized, double-blind trial.

BACKGROUND AND OBJECTIVES: Wound infiltration with available local anesthetics generally provides analgesia for less than 8 hrs. The site 1 sodium-channel toxin neosaxitoxin (neoSTX) produced analgesia for over 24 hrs in animals and human volunteers. In this randomized, double-blind trial, we examined the postoperative course of patients undergoing laparoscopic cholecystectomy under a standardized general anesthesia with wound infiltration using either neoSTX or bupivacaine. We hypothesized that neoSTX would reduce pain compared with bupivacaine at 12 hrs postoperatively. METHODS: Patients received preincisional infiltration of laparoscope entry sites with 20 mL containing either neoSTX (total dose, 100 µg) or bupivacaine 0.25% (total dose, 50 mg). The primary outcome measure was the visual analog pain score at 12 hrs postoperatively. Secondary outcomes included repeated pain scores at rest and with movement,analgesic use, functional recovery, and adverse effects. Groups were compared using Mann-Whitney U tests for pain scores, Fisher exact test for proportions of patients with severe pain and complete analgesia, and Kaplan-Meier curves for time to full recovery. RESULTS: Among 137 subjects, 69 were randomized to neoSTX and 68 to bupivacaine. Median pain scores at rest and with movement 12 hrs postoperatively were lower in the neoSTX group compared with the bupivacaine group (P<0.01). Additional pain measures and recovery parameters also favored neoSTX. No serious adverse events occurred,and no adverse events were more frequent in the neoSTX group. CONCLUSIONS: NeoSTX shows promise as a long-acting local anesthetic. Future studies will examine dose response, combination formulations, and safety with dose escalation.

Potentiation of local anesthetic activity of neosaxitoxin with bupivacaine or epinephrine: development of a long-acting pain blocker.

Local anesthetics effectively block and relieve pain, but with a relatively short duration of action, limiting its analgesic effectiveness. Therefore, a long-acting local anesthetic would improve the management of pain, but no such agent is yet available for clinical use. The aim of this study is to evaluate the potentiation of the anesthetic effect of neosaxitoxin, with bupivacaine or epinephrine in a randomized double-blind clinical trial. Ten healthy males were subcutaneously injected into the left and right forearms with a randomized pair of the following treatments: (i) bupivacaine (5 mg); (ii) neosaxitoxin (10 microg); (iii) neosaxitoxin (10 microg) plus bupivacaine (5 mg), and (iv) neosaxitoxin (10 microg) plus epinephrine (1:100.000), but all participant received all four formulations (in 2 ml; s.c.), with 1 month elapsing between the two round of experiments. A validated sensory and pain paradigm was used for evaluating the effect of the treatment 0-72 h after the injections, measuring sensory, pain, and mechanical touch perception threshold. The duration of the effect produced by combined treatments was longer than that by the single drugs. In conclusion, bupivacaine and epinephrine potentiate the local anesthetic effect of neosaxitoxin in humans when co-injected subcutaneously. The present results support the idea that neosaxitoxin is a new long-acting local pain blocker, with highly potential clinical use.

Evidence of in vitro glucuronidation and enzymatic transformation of paralytic shellfish toxins by healthy human liver microsomes fraction.

Paralytic Shellfish Toxins (PST) are endemic components found in filter bivalves in Southern Chile. Post-mortems analysis of fluid and tissue samples has shown biotransformation of PST in humans. The Gonyautoxin 3 (GTX3) and Gonyautoxin 2 (GTX2) are the major PST components in the toxin profile found in Chilean shellfish extracts, being as much as 65% of the total content of PST in filter bivalves. Therefore, they are the major accountable components of the human intoxication by shellfish consumption. The aim of this study is to show in vitro glucuronidation and biotransformation of GTX3 and GTX2 when they are incubated with microsomal fraction isolated from healthy human livers. Microsomes fractions isolated from human livers were incubated with GTX3 and GTX2 purified from contaminated mussels. After different incubation times, incubated samples were extracted and analyzed by HPLC with fluorescent on line detection and HPLC-MS analysis. The results revealed that GTX3 and GTX2, only when they were incubated with microsomal fraction and appropriated cofactors, showed to be enzymatic transformed in vitro. The glucuronidation of GTX3 and GTX2 followed typical Michaelis-Menten kinetics, resulting in apparent kinetic parameters of Km=39.4+/-0.24 microM and Vmax=6.0x10(-3) pmol/min/mg protein. In addition, the microsomes fraction also oxidized GTX3 and GTX2 into Gonyautoxin 4 (GTX 4) and Gonyautoxin 1 (GTX 1) resulting in 0.339x10(-3) pmol/min/mg protein. In conclusion, this study reports oxidation and glucuronidation of GTX3 and GTX2 when they are incubated with human liver microsomal fraction. The metabolism occurs via a glucuronidation reaction, the basis first step of biotransformation in human liver. Also it is showed that GTX4 and GTX1 came by biotransformation from GTX3 and GTX2 in humans. This data confirm human biotransformation found in human post-mortem fluid and tissue samples described previously. This data is the first evidence of in vitro glucuronidation of PST, given a metabolic pathway of detoxification and excretion of PST in human.

Videothoracoscopic management of middle esophageal diverticulum with secondary bronchoesophageal fistula: report of a case.

Middle esophageal diverticulum is rare, but can result in bronchoesophageal fistula. Previous reports have described open surgical techniques to treat esophageal diverticula, but few have evaluated the effectiveness of a videothoracoscopy approach. We report a case of middle esophageal diverticulum associated with bronchoesophageal fistula, managed successfully with videothoracoscopy. We also review the relevant literature.

Cirugía endoscópica transgástrica: experiencia inicial en modelos animales / Transgastric endoscopic surgery: initial experience in animal model

Natural orifice transluminal endoscopic surgery (notes), is a novel approach to the peritoneal cavity, that has been used for both diagnostic and surgical procedures. Aims: to evaluated the safety and feasibility of per-oral transgastric route for peritoneal approach and for several basic surgical techniques in a porcine experimental model. Material and methods: five pigs entered in the study. Under general anesthesia , a conventional endoscope was passed into the stomach, the gastric wall was punctured by mean of a sphincterotome and the size of the gastric incision was increased with a cholecystectomy and intestinal loops mobilization were attempted. Gastric incision closure was performed with endoloops. Results: a good observation of the peritoneal cavity was achieved. Liver samples were obtained in all procedures as well as mobilization of small intestinal loops. Cholecystectomy was possible in only three cases. Conclusion: transgastric approach to the peritoneal cavity seems to be a potential alternative to the classical laparotomy and laparoscopic technique.

La cirugía endoscópica transluminal por orificios naturales (NOTES) es un nuevo abordaje a la cavidad peritoneal que ha sido utilizada ya sea como procedimiento diagnóstico o quirúrgico. Objetivos: Evaluar la seguridad y factibilidad de la ruta per-oral transgástrica para el acceso a la cavidad peritoneal , y para la realización de técnicas quirúrgicas básicas en un modelo experimental porcino. Material y métodos: Se utilizaron cinco cerdos. Bajo anestesia general mediante un endoscopio convencional se accedió al estómago y se puncionó la pared gástrica mediante un papilótomo. La abertura se amplió ya sea con papilótomo o con balón. Se exploró la cavidad peritoneal y se intentó realizar: biopsias hepáticas en todos los procedimientos, lo mismo ocurrió con la movilización de asas intestinales. La colecistectomía fue posible en sólo tres ocasiones. Conclusión: el abordaje transgástrico de la cavidad peritoneal pareciera ser una potencial alternativa a la laparotomía clásica y laparoscópica.

Neosaxitoxin as a local anesthetic: preliminary observations from a first human trial.

BACKGROUND: Neosaxitoxin is a phycotoxin that reversibly blocks the voltage-gated sodium channels at the neuronal level. Its activity results in blocking the axonal conduction, stopping the propagation of the nerve impulse. The objective of the present work was to evaluate neosaxitoxin as a local anesthetic in a human trial. METHODS: The authors conducted a randomized, double-blind, placebo-controlled trial with 10 healthy volunteers. Subcutaneous injections were made in the middle posterior skin of the calf: one leg received 50 microg neosaxitoxin, and the contra-lateral leg received placebo. The anesthetic effect was evaluated using a standardized human sensory and pain model. TSA II Neurosensory Analyzer (Medoc Ltd, Minneapolis, MN) and von Frey technique were used to evaluate five parameters: sensory threshold for warm and cold, pain thresholds for heat and cold, and mechanical touch perception threshold. Measurements were made 0, 1, 3, 6, 9, 12, 16, 24, and 48 h after the injections. RESULTS: For all the patients, effective and complete blocking of the evaluated parameters was obtained. As the blocking began to revert gradually, heat pain was the first to return to normal values after 3 h. Cold pain was the longest sensation abolished, achieving 24 h of blockade. The toxin was undetected in blood and urine samples. No adverse reactions to neosaxitoxin were detected. CONCLUSIONS: Neosaxitoxin showed an effective local anesthetic effect when injected in the subcutaneous plane. The efficacy of a 50-microg dose of neosaxitoxin was shown. This is the first report of neosaxitoxin as a local anesthetic in a human trial.