Isobolographic analysis reveals antinociceptive synergism between Ph1 recombinant toxin and morphine in a model of cancer pain in C57BL/6J mice

Abstract Background: Phoneutria nigriventer venom contains Ph1. This toxin and its recombinant form have a remarkable analgesic potential that is associated with blockage of voltage-gated calcium channels and TRPA1 receptors. Although morphine is a mainstay drug to treat moderate and severe pain related to cancer, it has serious and dose-limiting side effects. Combining recombinant Ph1 and morphine to treat pain is an interesting approach that has been gaining attention. Therefore, a quantitative and reliable method to establish the strength of the antinociceptive interaction between these two substances is necessary. The present study was designed to investigate the nature of the functional antinociceptive (analgesic) interaction between Ph1 recombinant toxin and morphine in a model of cancer pain. Methods: Melanoma was produced by intraplantar inoculation of B16-F10 cells into the right paw of C57BL/6J mice. Von Frey filaments measured the paw-withdrawal threshold after intrathecal administration of morphine, recombinant Ph1, and their combination. Thermal hyperalgesia was assessed using Hargreaves apparatus. The degree of interaction was evaluated using isobolographic analysis. Spontaneous and forced motor performance was assessed with the open-field and rotarod tests, respectively. Results: Co-administration of recombinant Ph1 and morphine synergistically reverses the melanoma-induced mechanical hyperalgesia. The potency of the mixture, measured as the effective dose to reach 50% of maximum possible effect (MPE) in ameliorating mechanical hyperalgesia, was about twice fold higher than expected if the interaction between morphine and recombinant Ph1 was merely additive. Treatment with the combination at doses necessary to reach 50% of MPE caused no spontaneous nor forced motor alterations. Conclusion: The combinatorial use of recombinant Ph1 and morphine allows significant and effective dose reduction of both agents, which has translational potential for opioid-sparing approaches in pain management related to cancer.

The Interaction between Remifentanil and Propofol during Total Intravenous Anesthesia and the Adequate Effect Site Concentration / 대한마취과학회지

BACKGROUND: This study was performed to evaluate the interaction between remifentanil and propofol by comparing median-effect concentration (EC50) of single and co-administration, and to find adequate combination doses for general anesthesia for gastrectomy. METHODS: Thirty-six ASA physical status 1 or 2 patients scheduled for gastrectomy were randomly assigned to the remifentanil, propofol, or combination group.To obtain the dose-effect curve of remifentanil or propofol only, the effect site concentration of each drug was escalated until bispectral index (BIS) was reached 40 by a target-controlled infusion (TCI) during the steady operational period.For the combination group, 0.25, 0.5, 1, 2, and 2.5 timed EC50 of each drug were co-administered.The heart rate, mean arterial pressure and BIS were measured during the study period.The interaction between remifentanil and propofol was analyzed with using isobologram. RESULTS: The EC50 of remifentanil for hypnosis (BIS 40) was 1.96 ng/ml, and that of propofol was 1.35microgram/ml.In the combination group, the EC50 of remifentanil was 0.81 ng/ml and that of propofol was 0.56microgram/ml.EC90 of remifentanil and propofol alone were 13.43 ng/ml and 4.88microgram/ml. For EC90 of the combination group, remifentanil 3.54 ng/ml and propofol 2.50 microgram/ml were required.The distance from the theoretical additive line in the isobologram was larger in the higher doses (EC50 < EC75 < EC90). CONCLUSIONS: This study shows that remifentanil and propofol reveal synergism by isobolographic analysis during intravenous anesthesia.

Drug Interactions of Intrathecal Carbachol and Clonidine in Neuropathic Pain Model of the Rats / 대한마취과학회지

BACKGROUND: After peripheral nerve injury in human, a syndrome of events (spontaneous pain, allodynia and hyperalgesia) may be observed that includes no response of morphine and dependency of this pain state on intact sympathetic function. Spinally delivered 2-adrenoceptor agonist and cholinergic agonist or cholinesterase inhibitors have been shown to have actions attenuating the hyperalgesia in rat models of nerve injury-induced pain. Using a fixed-dose analysis and an isobolographic paradigm, the spinal interaction between the 2-adrenoreceptor agonist, clonidine and cholinergic agonist, carbachol is characterized in rat model of nerve injury-induced tactile hyperalgesia. METHODS: Male Sprague Dawely rats were anesthetized with halothane, and the left L5 and L6 spinal nerve were ligated (Chung model). After recovery, a polyethylene tubing catheter was implanted into lumbar intrathecal space. After recovery from catheter implantation, intrathecal dose-response curves were established for the antiallodynic effect of carbachol (0.1, 0.3, 1.0, 3.0 microgram) and clonidine (0.3, 1.0, 3.0, 10 microgram) alone to obtain the ED50 for each agent. ED50 fractions (1/2, 1/4, 1/8, 1/16) of drug combinations of carbachol-clonidine were administered and thresholds for left hind limb paw withdrawal to von Frey hair application were assessed. The ED50 of carbachol-clonidine combination was established and isobolographic analysis of the drug interactions was carried out.c RESULTS: Intrathecal carbachol and clonidine alone produced dose-dependent reductions of tactile allodynia: ED50 of 66 ng (12~367 ng) and 39 ng (1~1452 ng), respectively. With the fixed dose analysis, the log dose-response curves showed a left shift that considerably exceeds the theoretical curves made by a simple sum of the effects of carbachol alone and clonidine. With the isobolographic analysis, ED50 of mixture was found to be statistically less than the theoretical additive ED50 of mixture. CONCLUSION: The experiments suggest that intrathecal carbachol and clonidine alone produce a dose dependent antagonism on touch evoked allodynia and intrathecal carbachol is synergistic when combined with intrathecal clonidine.

Isobolographic analysis of hypnotic interaction between propofol and ketamine / 中华麻醉学杂志

Objective To study the hypnotic interaction between propofol and ketamine with isobologram. Methods Seventy-five ASA Ⅰ - Ⅱ patients (35 male, 40 female) aged 20-50 yr, weighing 40-80 kg, undergoing elective upper abdominal surgery were randomly divided into three equal groups of 25 patients : propofol group (P); ketamine group (K) and propofol-ketamine combination group (P/K), Each group was further divided into 5 subgroups. Propofol 0.8, 1.0, 1.25, 1.56 or 1.95 mg ? kg-1 was given in 5 propofol subgroups (P1-5 ) respectively. Ketamine 0.32, 0.40, 0.50, 0.63 or 0.78 mg?kg-1 was given in 5 ketamine subgroups (K1-5 ) respectively. Propofol /ketamine 0.45/0.15, 0.60/0.20, 0.80/0.29, 1.05/0.35 or 1.41/0.47 mg?kg-1 were given in the 5 propofol-ketamine combination subgroups (P/K1-5 ) respectively. Two minutes after drug administration the patients were asked to open their eyes. Failure to open eyes was taken as the start-point of hypnotic effect. If the patient failed to respond to verbal order twice consecutively, the patient was considered to be in the hypnotic state. When the patient in hypnotic state failed to respond to electric stimulation of certain intensity, the patient was considered to be in anesthetic state. ED50s of propofol, ketamine and P/K combination for hypnotic and anesthetic effect were calculated. Isobologram was drawn. ED50 and 95 % confidence limit of ketamine were plotted on the abscissa and of propofol on the ordinate. The ED50 s of the two drugs were connected. If the ED50 of P/K combination was located on the connecting line, the two drugs are additive, on the left side of the connecting line synergistic, on the right side of the connecting line antagonistic. SBP, DBP, HR, SpO2 and BIS were continuously monitored before, during and after drug administration. Results The ED50 s for hypnotic and anesthetic effect were : 1.15 mg? kg-1 and 1.59 mg? kg-1 in group P; 0.40 mg? kg-1 and 0.72 mg? kg-1 in ketamine group; 0.65/0.22 mg?kg-1 and 1.19/0.40 mg?kg-1 in P/K group. The deviation of the location of ED50 of P/K combination from the connecting line was statistically insignificant. There was no significant change in SBP and DBF after administration of drugs in P/K group. Conclusion The hypnotic and anesthetic interaction between propofol and ketamine was additive. In terms of hemodynamic stability, P/K combination was the best among the three groups.