Isobolographic analysis of the analgesic interactions between ketamine and tramadol

Discovery of a Novel Orally Active Ketamine Derivative with Dual Analgesic and Antidepressant Activities, Lacking Psychomimetic Effects

This study investigated the synthesis, characterization, and in silico analysis of novel N-acetamide ketamine derivatives aimed at evaluating their analgesic, anesthetic, and antidepressant properties. The synthesis commenced with the preparation of chloroacetylamide derivatives, which were subsequently reacted with ketamine hydrochloride, yielding 16 derivatives k1 to k16. These compounds were characterized through H1 NMR, C13 NMR, mass spectroscopy (EIMS), and elemental analysis, followed by an assessment of their physicochemical properties. The analgesic efficacy of all of the synthesized derivatives was evaluated using the acetic acid-induced writhing test via intraperitoneal administration. The best-performing molecule was further evaluated for analgesic (acetic acid-induced writhing test, tail suspension test (TST), and hot plate test) and anti-inflammatory (carrageenan-induced paw edema) activities. For antidepressant effects, all derivatives were compared with ketamine in a lipopolysaccharide-induced model of depression in mice through the forced swimming test, open field test (OFT), sucrose preference test (SPT), and TST. It was observed that among all the derivatives, molecule k1 demonstrated comparable analgesic activity to ketamine. Further, compound k1 also exhibited the highest antidepressant potential during the forced swimming test, OFT, SPT, and TST. k1 was further compared with ketamine for their activities intraperitoneally and orally where k1 exhibited comparable antidepressant effects to ketamine. Henceforth, the psychomimetic potential of k1 was evaluated through loss of righting reflex and Y-maze tests. Very interestingly, these tests indicated approximately no psychomimetic activity of k1 compared to ketamine intraperitoneally and orally. Finally, molecular docking studies were conducted targeting the NMDA receptor at the JC09 ketamine binding pocket (PDB ID: 7EU7), where all synthesized derivatives exhibited significant binding affinities relative to ketamine. These findings suggest that the newly synthesized N-acetamide ketamine derivative k1 possesses promising pharmacological profiles, warranting further exploration.

Esketamine Anesthetizes Mice With a Similar Potency to Racemic Ketamine

Esketamine, the right-handed optical isomer of racemic ketamine, has recently become widely used for anesthesia and analgesia as a replacement for racemic ketamine. However, there are limited studies comparing the anesthetic and analgesic effects of esketamine and racemic ketamine in mice. This research was conducted to analyze the dose-dependent anesthetic and analgesic efficacy of esketamine in mice and to compare its potency with that of the racemate. We tested the anesthetic effects of different doses of esketamine and compared its potency with that of the racemate using righting reflex tests. Then, the acetic acid-induced pain model and formalin-induced pain model were used to investigate the analgesic effect. Compared with racemic ketamine, an equivalent dose of esketamine at 100 mg/kg was required to induce stable anesthesia. In contrast, 5 mg/kg esketamine was sufficient to provide analgesic effects similar to those of 10 mg/kg ketamine. Together, esketamine had a similar potency to racemic ketamine for anesthesia and a stronger potency for analgesia in mice.

Revisiting Tramadol: A Multi-Modal Agent for Pain Management

Tramadol-an atypical opioid analgesic-has a unique pharmacokinetic and pharmacodynamic profile, with opioidergic, noradrenergic, and serotonergic actions. Tramadol has long been used as a well-tolerated alternative to other drugs in moderate pain because of its opioidergic and monoaminergic activities. However, cumulative evidence has been gathered over the last few years that supports other likely mechanisms and uses of tramadol in pain management. Tramadol has modulatory effects on several mediators involved in pain signaling, such as voltage-gated sodium ion channels, transient receptor potential V1 channels, glutamate receptors, α₂-adrenoceptors, adenosine receptors, and mechanisms involving substance P, calcitonin gene-related peptide, prostaglandin E₂, and proinflammatory cytokines. Tramadol also modifies the crosstalk between neuronal and non-neuronal cells in peripheral and central sites. Through these molecular effects, tramadol could modulate peripheral and central neuronal hyperexcitability. Given the broad spectrum of molecular targets, tramadol as a unimodal analgesic relieves a broad range of pain types, such as postoperative, low back, and neuropathic pain and that associated with labor, osteoarthritis, fibromyalgia, and cancer. Moreover, tramadol has anxiolytic, antidepressant, and anti-shivering activities that could improve pain management outcomes. The aim of this review was to address these issues in the context of maladaptive physiological and psychological processes that are associated with different pain types.

The analgesic interaction of tramadol and morphine in rats: An isobolographic study

In order to assess possible synergistic antinociceptive interactions, the analgesic effects of intra-peritoneal tramadol and morphine administered either separately or in combination were determined using tail-flick latency test following exposure to radiant heat in rats. Groups of eight male Sprague-Dawley rats received either tramadol (3.90, 7.00, 12.50, and 22.20 mg kg^-1) and morphine (1.26, 2.25, 4.00 and 7.10 mg kg^-1) or a combination of tramadol and morphine (4 different combinations). The baseline latency was obtained before drug injection for each rat, then at 15, 30, 45, 60 and 75 min after injection. The effective dose (ED)₅₀ for either tramadol or morphine individually was 11.70 mgkg^-1 and 2.26 mg kg^-1, respectively. Based on isobolographic analysis, the ED₅₀ values obtained by drug combination were significantly less than the calculated additive values; which indicates that the co-administration of tramadol and morphine produces synergistic antinociception in the radiant heat tail-flick assay. Combination of morphine and tramadol administered intra-peritoneally can be used for the control of acute pain in rats.

The Antinociceptive Effect of a Tapentadol-Ketorolac Combination in a Mouse Model of Trigeminal Pain is Mediated by Opioid Receptors and ATP-Sensitive K+ Channels

Preclinical Research The aim of the present study was to evaluate the antinoceptive interaction between the opioid analgesic, tapentadol, and the NSAID, ketorolac, in the mouse orofacial formalin test. Tapentadol or ketorolac were administered ip 15 min before orofacial formalin injection. The effect of the individual drugs was used to calculate their ED50 values and different proportions (tapentadol-ketorolac in 1:1, 3:1, and 1:3) were assayed in the orofacial test using isobolographic analysis and interaction index to evaluate the interaction between the drugs. The combination showed antinociceptive synergistic and additive effects in the first and second phase of the orofacial formalin test. Naloxone and glibenclamide were used to evaluate the possible mechanisms of action and both partially reversed the antinociception produced by the tapentadol-ketorolac combination. These data suggest that the mixture of tapentadol and ketorolac produces additive or synergistic interactions via opioid receptors and ATP-sensitive K+ channels in the orofacial formalin-induced nociception model in mice. Drug Dev Res 78 : 63-70, 2017. © 2016 Wiley Periodicals, Inc.

Antinociceptive effect and interaction of uncompetitive and competitive NMDA receptor antagonists upon capsaicin and paw pressure testing in normal and monoarthritic rats

We assessed whether intrathecal administration of the uncompetitive and competitive NMDA receptor antagonists ketamine and (+/-)CPP, respectively, could produce differential modulation on chemical and mechanical nociception in normal and monoarthritic rats. In addition, the antinociceptive interaction of ketamine and (+/-)CPP on monoarthritic pain was also studied using isobolographic analysis. Monoarthritis was produced by intra-articular injection of complete Freund's adjuvant into the tibio-tarsal joint. Four weeks later, the antinociceptive effect of intrathecal administration of the drugs alone or combined was evaluated by using the intraplantar capsaicin and the paw pressure tests. Ketamine (0.1, 1, 10, 30, 100, 300 and 1000 microg i.t.) and (+/-)CPP (0.125, 2.5, 7.5, 12.5, 25 and 50 microg i.t.) produced significantly greater dose-dependent antinociception in the capsaicin than in the paw pressure test. Irrespective of the nociceptive test employed, both antagonists showed greater antinociceptive activity in monoarthritic than in healthy rats. Combinations produced synergy of a supra-additive nature in the capsaicin test, but only additive antinociception in paw pressure testing. The efficacy of the drugs, alone or combined, is likely to depend on the differential sensitivity of tonic versus phasic pain and/or chemical versus mechanical pain to NMDA antagonists.

The Addition of a Small-Dose Ketamine Infusion to Tramadol for Postoperative Analgesia: A Double-Blinded, Placebo-Controlled, Randomized Trial After Abdominal Surgery

BACKGROUND

There are few data on combining ketamine with tramadol for postoperative analgesia in humans. We tested the hypothesis that adding ketamine to tramadol would improve analgesia after major abdominal surgery.

METHOD

In this double-blind, randomized, controlled trial, adult patients (n = 120) having elective laparotomy were randomly assigned to a ketamine group (intraoperative ketamine 0.3 mg/kg and postoperative infusion at 0.1 mg x kg(-1) x h(-1) or control group (equivalent volume/rate of normal saline). All patients received intraoperative tramadol 3 mg/kg and a tramadol infusion (0.2 mg x kg(-1) x h(-1) for 48 h postoperatively and had morphine patient-controlled analgesia available for rescue analgesia.

RESULTS

The ketamine group had less pain at rest (P = 0.01) and with movement (P = 0.02) and required less morphine (P = 0.003) throughout the 48-h study period. In the 0-24 h period, ketamine improved subjective analgesic efficacy (P = 0.008), was less sedating (P = 0.03), and required fewer physician interventions to manage severe pain (P = 0.01). Hallucinations were more common in ketamine patients, but other side effects were similar.

CONCLUSION

Small-dose ketamine was a useful addition to tramadol and morphine after major abdominal surgery.

Isobolographic analysis of the dual-site synergism in the antinociceptive response of tramadol in the formalin test in rats

Tramadol is an atypical opioid with a complex mechanism of action including a synergistic interaction between the parent drug and an active metabolite. The local action of the parent drug is poorly documented. This study was designed to evaluate the site-site interaction of the antinociception produced by tramadol given by two different routes. The effects of individual and fixed-ratio combinations of intraplantar (i.pl.) and intraperitoneal (i.p.) tramadol were evaluated using the formalin test in rats. Isobolographic analysis was employed to identify the synergy produced by combinations. In both first and second phases of the formalin test, tramadol was active not only by the systemic (ED50 10.2+/-2.1 and 7.1+/-0.5 mg/kg i.p.) but also by the local route (ED50 171.0+/-44.8 and 134.6 microg/paw i.pl.). The isobolographic analysis revealed a "self-synergism" in the antinociceptive effect between the two routes of administration, as the experimental ED50 (211.1+/-13.6 and 45.9+/-3.9 "dose units" phase 1 and 2, respectively) of the combination was significantly lower than the theoretical ED50 (422.2+/-50.5 and 138.5+/-9.2 "dose units"). The mechanism underlying this self-synergism appears to be partially opioid since systemic but not local naloxone reversed the potentiation. The observed dual-site interaction in the antinociceptive action of tramadol provides insights for alternatives in the management of pain.