The Science of Local Anesthesia

Local anesthetics for the Nephrologist

Several specialists in medicine use local anesthetics. In patients with kidney disease, these agents are used during catheter insertions for hemodialysis and peritoneal dialysis, arteriovenous fistula and graft procedures, kidney transplantation, parathyroidectomy, kidney biopsies, and dental and skin procedures. Patients on chronic hemodialysis use a topical application prior to use of needles for arteriovenous fistula cannulation before starting dialysis. They are also used to manage acute and chronic pain conditions, in regional nerve blockade and in multi-modal enhanced recovery protocols. Despite their frequent use by both physicians and patients, data on the use of local anesthetics in patients with kidney impairment are not well reported. This review will summarize the use of local anesthetics in chronic kidney disease, describe their pharmacology and the impact of lower estimated glomerular filtration rate on their pharmacokinetics, and suggest dose regulation in those with kidney dysfunction.

Comprehensive Analysis to Identify the Encoded Gens of Sodium Channels as a Prognostic Biomarker in Hepatocellular Carcinoma

The SCN family as the encoded gens of sodium channels has been proven to participate in development of cancers including hepatocellular carcinoma (HCC), but the prognostic value of the SCN family is unclear. The results of the UALCAN database had showed that SCN2A/4A/5A/8A mRNA were highly expressed in tumour tissues, while SCN1A/7A/11A mRNA were expressed at low levels (p < 0.05), furthermore, the expression of SCN4A and SCN7A had the similar levels in microarray analysis result. The pan-tumour analysis showed that SCN7A expression was stably lower in tumours than SCN4A expression by TIMER. Both SCN4A and SCN7A were related to tumour grade, nodal metastatic status, histological subtype, patient race, individual cancer stages and TP53 mutation status to varying degrees. The Kaplan–Meier plotter demonstrated that high SCN4A mRNA expression was correlated with better overall survival (OS), disease-specific survival (DSS) and progression-free survival (PFS) and that high expression of SCN7A mRNA was associated with better OS; however, in Asians, higher SCN4A was correlated with better OS and DSS, and higher SCN7A was well correlated with better OS, recurrence-free survival (RFS), DSS and PFS. Analysis of data from cBioPortal showed that mutation of SCN7A was related to RFS and PFS. The protein expression of SCN4A and SCN7A had been detected by Immunohistochemistry. Univariate survival analysis revealed that high SCN7A protein expression was significantly linked to better OS (p = 0.001) and RFS (p = 0.003). Moreover, SCN7A displayed as an independent prognostic factor by multivariate analysis. In addition, a lower methylation level indicated a poor outcome. Pathway and functional enrichment analysis predicted a relationship between SCN7A and the PI3K pathway. In conclusion, there are significant and stable changes in SCN4A and SCN7A expression in HCC. SCN7A expression has better prognostic value and might participate in HCC progression.

Predictive value of immediate pain relief after lumbar transforaminal epidural injection with local anesthetics and steroids for single level radiculopathy

OBJECTIVE

To assess the predictive value of immediate pain-relief after CT-guided transforaminal epidural steroid injection (TFESI) including local anesthetics for longer-term pain relief and patients' global impression of change (PGIC) after 4 weeks.

MATERIALS AND METHODS

One hundred ninety-three patients (age 55.4 ± 14.9) with single-level discogenic lumbar radiculopathy and subsequent TFESI were included. Pain scores were recorded before (NRS₀), 15 min (NRS_15min), and 4 weeks (NRS_4w) after treatment using a numerical-rating-scale (NRS; 0, no pain; 10, intolerable pain). Additionally, the PGIC was assessed after 4 weeks. Two fellowship-trained musculoskeletal radiologists evaluated nerve compression of the injected level and contrast dispersion. Spearman's rank and point-biserial correlation were applied to assess associations between outcome variables and demographics/imaging findings. A p-value < 0.05 was considered to be statistically significant.

RESULTS

There was a significant positive correlation between immediate pain-relief and longer-term pain-reduction (r = 0.24, p = 0.001) with an odds ratio of 2.0 (CI: 1.1-3.6). A good short-term response (NRS_15min ≥ 50% reduction) was associated with a persistent longer-term good response (NRS_4w ≥ 50% reduction) in 59.7% (CI: 50.9-68.0%) of patients. There was no association between short-term pain-relief and PGIC after 4 weeks (p = 0.18). Extent and location of nerve compression and contrast dispersion during TFESI did not correlate with longer-term pain-relief (all p ≥ 0.07).

CONCLUSION

Our results indicate a significant positive correlation between immediate post-procedural and longer-term pain relief after TFESI in patients with lumbar radiculopathy; however, no effect of short-term pain relief is seen on PGIC after 4 weeks. Patients with good longer-term outcome (≥ 50% pain reduction) are twice as likely to have already shown good immediate pain reduction after TFESI.

The Options for Neuraxial Drug Administration

Neuraxial drug administration, i.e., the injection of drugs into the epidural or intrathecal space to produce anesthesia or analgesia, is a technique developed more than 120 years ago. Today, it still is widely used in daily practice in anesthesiology and in acute and chronic pain therapy. A multitude of different drugs have been introduced for neuraxial injection, only a part of which have obtained official approval for that indication. A broad understanding of the pharmacology of those agents is essential to the clinician to utilize them in a safe and efficient manner. In the present narrative review, we summarize current knowledge on neuraxial anatomy relevant to clinical practice, including pediatric anatomy. Then, we delineate the general pharmacology of neuraxial drug administration, with particular attention to specific aspects of epidural and intrathecal pharmacokinetics and pharmacodynamics. Furthermore, we describe the most common clinical indications for neuraxial drug administration, including the perioperative setting, obstetrics, and chronic pain. Then, we discuss possible neurotoxic effects of neuraxial drugs, and moreover, we detail the specific properties of the most commonly used neuraxial drugs that are relevant to clinicians who employ epidural or intrathecal drug administration, in order to ensure adequate treatment and patient safety in these techniques. Finally, we give a brief overview on new developments in neuraxial drug therapy.

The impact of dexamethasone as a perineural additive to ropivacaine for PECS II blockade in patients undergoing unilateral radical mastectomy - A prospective, randomized, controlled and double-blinded trial

STUDY OBJECTIVE

Dexamethasone is commonly used as an adjuvant to local anesthetics to prolong duration of peripheral nerve blocks with minimal side-effects. The present study investigates the efficacy of dexamethasone added to ropivacaine 0.2% as compared to ropivacaine 0.2% alone for pectoral nerves block II (PECS II) in unilateral radical mastectomy.

DESIGN

A prospective, randomized, controlled and double-blinded trial.

SETTING

The study was performed at Innsbruck Medical University Hospital, Austria, between January 2019 and October 2020.

PATIENTS

Sixty female patients with an American Society of Anesthesiologists Score I-II (18-90 years, BMI 18-35) scheduled for unilateral radical mastectomy without one-stage immediate autologous breast reconstruction were randomly assigned to receive PECS II block with ropivacaine 0.2% with or without dexamethasone 8 mg.

INTERVENTIONS

Patients were randomly assigned to receive PECS II block with ropivacaine 0.2% with or without dexamethasone 8 mg.

MEASUREMENTS

Primary outcome parameter was the cumulative opioid consumption during the first 72 postoperative hours. Secondary outcome parameters were the duration of analgesia and the course of the visual analogue scale (VAS) and the area under the curve VAS (AUC-VAS).

MAIN RESULTS

There was no difference in cumulative opioid consumption after 72 h between the ropivacaine 0.2% plus dexamethasone group and the ropivacaine 0.2% plus placebo group (11.89 vs 11.90 morphine milligram equivalent, respectively; p 0.831). Duration of analgesia also did not differ significantly between the ropivacaine 0.2% plus dexamethasone group and the ropivacaine 0.2% plus placebo group (12.75 versus 8.75 h, respectively; p 0.680). There also was no difference in the course of VAS and AUC-VAS.

CONCLUSIONS

Dexamethasone 8 mg when added to ropivacaine 0.2% for PECS II block in unilateral radical mastectomy was not found to reduce total opioid consumption over 72 postoperative hours or to prolong duration of analgesia as compared to pure ropivacaine 0.2%.

Ropivacaine suppresses tumor biological characteristics of human hepatocellular carcinoma via inhibiting IGF-1R/PI3K/AKT/mTOR signaling axis

Ropivacaine, a common local anesthetic in the clinic, has anti-proliferative and pro-apoptotic effects in numerous cancers, however, the underlying regulatory mechanism of ropivacaine in hepatocellular carcinoma remains unclear. In the current study, human HepG2 cells were stimulated with different ropivacaine concentrations. Cell Counting Kit-8 assay, cell colony formation, and cell cycle were used to monitor cell viability. Cell apoptosis, migration, and invasion were determined by flow cytometry and transwell assays. Tumor xenograft experiments were performed to prove the anti-cancer effect of ropivacaine in vivo. A high dose of ropivacaine inhibited proliferation and promoted apoptosis of HepG2 cells in a dose-dependent manner. Ropivacaine challenge also arrested cells in the G2 phase, followed by a decline in the protein expression of cyclin D1 and cyclin-dependent kinase 2, and an increase in p27 levels in HepG2 cells. Additionally, different ropivacaine doses suppressed cell migration and invasion by upregulating E-cadherin expression and downregulating N-cadherin expression. Mechanically, ropivacaine challenge gradually restrained insulin-like growth factor-1 receptor (IGF-1 R) expression and the activities of phosphorylated-PI3K, AKT, and mTOR in HepG2 cells with increased ropivacaine doses. In the tumor xenograft experiment, ropivacaine was confirmed to inhibit tumor growth, accompanied by inhibition of the IGF-1 R/PI3K/AKT/mTOR signaling axis. In conclusion, ropivacaine suppressed tumor biological characteristics and promoted apoptosis, resulting in the suppression of hepatocellular carcinoma progression by targeting the IGF-1 R/PI3K/AKT/mTOR signaling pathway. It is possible that ropivacaine-mediated local anesthesia may be developed as a novel surgical adjuvant drug for treating hepatocellular carcinoma.

Antimalarial primaquine for spinal sensory and motor blockade in rats

OBJECTIVES

The purpose of the experiment was to estimate whether intrathecal antimalarial drugs could provoke spinal block, and their comparison with lidocaine.

METHODS

Rats were intrathecally administrated with antimalarial agents (primaquine, chloroquine, hydroxychloroquine and amodiaquine) and lidocaine, and neurobehavioural examinations (nociception, proprioception and motor function) were assessed; n = 8 per group. One-way and two-way analysis of variance were designed to analyse data.

KEY FINDINGS

At a concentration of 20 mM, primaquine (0.46 mg/rat) exhibited the longest duration and the most potent effect of nociceptive, proprioceptive and motor blockade (P < 0.01) among five drugs, whereas the other antimalarial drugs displayed a lesser or similar potency of spinal blockade compared with lidocaine (0.29 mg/rat). In dose-dependent studies, primaquine was more potent (P < 0.01) than lidocaine for spinal block. At ED25, ED50 and ED75 equipotent doses, primaquine produced a greater duration of spinal motor, proprioceptive and nociceptive blockade when compared with lidocaine (P < 0.01).

CONCLUSIONS

Primaquine, chloroquine, hydroxychloroquine and amodiaquine produced spinal blockade. Primaquine was more potent and displayed a prolonged life of local anaesthetic effect compared with lidocaine, whereas the other antimalarial drugs displayed a lesser or similar potency compared with lidocaine.

Lido-OH, a Hydroxyl Derivative of Lidocaine, Produced a Similar Local Anesthesia Profile as Lidocaine With Reduced Systemic Toxicities

Background: lidocaine is one of the most commonly used local anesthetics for the treatment of pain and arrhythmia. However, it could cause systemic toxicities when plasma concentration is raised. To reduce lidocaine’s toxicity, we designed a hydroxyl derivative of lidocaine (lido-OH), and its local anesthesia effects and systemic toxicity in vivo were quantitively investigated.

Method: the effectiveness for lido-OH was studied using mouse tail nerve block, rat dorsal subcutaneous infiltration, and rat sciatic nerve block models. The systemic toxicities for lido-OH were evaluated with altered state of consciousness (ASC), arrhythmia, and death in mice. Lidocaine and saline were used as positive and negative control, respectively. The dose-effect relationships were analyzed.

Results: the half effective-concentration for lido-OH were 2.1 mg/ml with 95% confident interval (CI95) 1.6–3.1 (lidocaine: 3.1 mg/ml with CI95 2.6–4.3) in tail nerve block, 8.2 mg/ml with CI95 8.0–9.4 (lidocaine: 6.9 mg/ml, CI95 6.8–7.1) in sciatic nerve block, and 5.9 mg/ml with CI95 5.8–6.0 (lidocaine: 3.1 mg/ml, CI95 2.4–4.0) in dorsal subcutaneous anesthesia, respectively. The magnitude and duration of lido-OH were similar with lidocaine. The half effective doses (ED₅₀) of lido-OH for ACS was 45.4 mg/kg with CI95 41.6–48.3 (lidocaine: 3.1 mg/kg, CI95 1.9–2.9), for arrhythmia was 16.0 mg/kg with CI95 15.4–16.8 (lidocaine: 3.0 mg/kg, CI95 2.7–3.3), and for death was 99.4 mg/kg with CI95 75.7–124.1 (lidocaine: 23.1 mg/kg, CI95 22.8–23.4). The therapeutic index for lido-OH and lidocaine were 35.5 and 5.6, respectively.

Conclusion: compared with lidocaine, lido-OH produced local anesthesia at similar potency and efficacy, but with significantly reduced systemic toxicities.

The 14-day repeated-dose toxicity studies of a fixed-dose combination, QXOH/levobupivacaine, via subcutaneous injection in mice

QXOH-LB, a fixed-dose combination (35 mM QXOH and 10 mM levobupivacaine) has been shown to induce a long duration of local anesthesia in animal efficacy testing, which indicates potential for postoperative pain management. In this study, we evaluated the potential toxicity of QXOH-LB in NIH mice under the Guidance on the repeated-dose toxicity published by the China Food and Drug Administration. Mice (n = 30 per sex per group) were subcutaneously injected 5, 10, 20 mg/kg QXOH-LB, 5, 10, 20 mg/kg QXOH, and 5 mg/kg levobupivacaine (LB) once a day for 14 days with sacrifice of main study animals; remaining mice (n = 10 per sex per group) were monitored for an additional 4-week recovery period. Mice in the 10 and 20 mg/kg QXOH, and 20 mg/kg QXOH-LB died, which was considered due to excessive respiratory inhibition. The doses of 10 mg/kg QXOH-LB and 5 mg/kg QXOH were well tolerated without any clinical signs of toxicity. Therefore, the no-observed-adverse-effect level (NOAEL) of QXOH-LB and QXOH was considered to be 10 and 5 mg/kg/day, respectively. In the dose range from 5 to 20 mg/kg, the exposure of QXOH and LB in QXOH-LB was equal to each agent used alone at the same dose in NIH mice. There was no gender difference on exposure and no evidence of accumulation.

Antimalarial primaquine for skin infiltration analgesia in rats

OBJECTIVES

The purpose of this study was to estimate the ability of antimalarial medications to induce local infiltration analgesia.

METHODS

Using a rat model of skin infiltration anaesthesia, the effects of antimalarial medications (primaquine, chloroquine, hydroxychloroquine and amodiaquine) were compared with the application of lidocaine.

KEY FINDINGS

At a dose of 3 μmol, primaquine and chloroquine displayed better potency (all P < 0.05) and greater duration (all P < 0.01) of cutaneous analgesia than lidocaine, whereas the other antimalarial medications showed a similar potency and duration of cutaneous analgesia when compared with lidocaine. When a dose of 3 μmol antimalarial medication was used, primaquine was the most potent and had the longest duration of action among four antimalarial medications. The relative potency ranking (ED50, 50% effective dose) has been found to be primaquine [2.10 (1.87 - 2.37) μmol] > lidocaine [6.27 (5.32 -7.39) μmol] (P < 0.01). Infiltration analgesia of skin with primaquine had a greater duration of action than did lidocaine on the equipotent (ED25, ED50, ED75) basis (P < 0.01).

CONCLUSIONS

Primaquine and chloroquine have greater potency and longer lasting skin analgesia when compared with lidocaine, while the other antimalarials display a similar potency in comparison with lidocaine.

Brachial Plexus Block with Liposomal Bupivacaine for Shoulder Surgery Improves Analgesia and Reduces Opioid Consumption: Results from a Multicenter, Randomized, Double-Blind, Controlled Trial

OBJECTIVE

The utility of single-injection and continuous peripheral nerve blocks is limited by short duration of analgesia and catheter-related complications, respectively. This double-blind, multicenter trial evaluated the efficacy, safety, and pharmacokinetics of single-injection, ultrasound-guided brachial plexus block (BPB) with liposomal bupivacaine (LB) added to a standardized pain management protocol for shoulder surgery.

METHODS

Adults undergoing total shoulder arthroplasty or rotator cuff repair were randomized to receive LB 133 mg, LB 266 mg (pharmacokinetic and safety analyses only), or placebo, added to a standardized analgesia protocol. The primary end point was area under the curve (AUC) of visual analog scale pain intensity scores through 48 hours postsurgery. Secondary end points were total opioid consumption, percentage of opioid-free patients, and time to first opioid rescue through 48 hours. Pharmacokinetic samples were collected through 120 hours and on days 7 and 10. Adverse events were documented.

RESULTS

One hundred fifty-five patients received treatment (LB 133 mg, N = 69; LB 266 mg, N = 15; placebo, N = 71). BPB with LB 133 mg was associated with significantly improved AUC of pain scores (least squares mean [SE] = 136.4 [12.09] vs 254.1 [11.77], P < 0.0001), opioid consumption (least squares mean [SE] = 12.0 [2.27] vs 54.3 [10.05] mg, P < 0.0001), median time to opioid rescue (4.2 vs 0.6 h, P < 0.0001), and percentage of opioid-free patients (treatment difference = 0.166, 95% confidence interval = 0.032-0.200, P = 0.008) through 48 hours vs placebo. Adverse event incidence was comparable between groups.

CONCLUSIONS

Single-injection BPB with LB 133 mg provided analgesia through 48 hours postsurgery with reduced opioid use compared with placebo after shoulder surgery.

Future in regional anesthesia and pain medicine: the pharmacological view

Local anesthetics are still incompletely understood, and none of the currently available drugs are optimal. The primary target of local anesthetics is the voltage-gated sodium channel (VGSC), where they lead to a temporary interruption of nerve conduction. Unfortunately, local anesthetics are neither specific at blocking a specific VGSC isoform, nor a specific cell type. We realize now that the old classification of A and C fibers according to myelin thickness is outdated, that next to differing myelin configuration, cells differ also by their molecular biology, and that there are close to 20 different neuronal subgroups when function is concerned. The ideal local anesthetic would only block sensory impulses, or even only painful impulses. In the search for that drug, several research avenues have been followed. First, efforts have been undertaken to extend duration of local anesthetics, by additives or extended-release formulation. Second, blockade of specific pain fibers has been attempted by targeting permanently charged anesthetics specifically into nociceptors. Third, blockade of specific isoforms using antibodies, and adaptation of naturally occurring neurotoxins has shown promise. Lastly, combination of local anesthetics with other analgesics may improve their duration of action.

Effect of tertiary amine local anesthetics on G protein-coupled receptor lateral diffusion and actin cytoskeletal reorganization

Although widely used clinically, the mechanism underlying the action of local anesthetics remains elusive. Direct interaction of anesthetics with membrane proteins and modulation of membrane physical properties by anesthetics are plausible mechanisms proposed, although a combination of these two mechanisms cannot be ruled out. In this context, the role of G protein-coupled receptors (GPCRs) in local anesthetic action is a relatively new area of research. We show here that representative tertiary amine local anesthetics induce a reduction in two-dimensional diffusion coefficient of the serotonin_1A receptor, an important neurotransmitter GPCR. The corresponding change in mobile fraction is varied, with tetracaine exhibiting the maximum reduction in mobile fraction, whereas the change in mobile fraction for other local anesthetics was not appreciable. These results are supported by quantitation of cellular F-actin, using a confocal microscopic approach previously developed by us, which showed that a pronounced increase in F-actin level was induced by tetracaine. These results provide a novel perspective on the action of local anesthetics in terms of GPCR lateral diffusion and actin cytoskeleton reorganization.

KM-416, a novel phenoxyalkylaminoalkanol derivative with anticonvulsant properties exerts analgesic, local anesthetic, and antidepressant-like activities. Pharmacodynamic, pharmacokinetic, and forced degradation studies

Anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic, neuropathic pain. We obtained a phenoxyalkylaminoalkanol derivative, KM-416 which had previously demonstrated a significant anticonvulsant activity and had also been shown to bind to 5-HT_1A, α₂-receptors and SERT and not to exhibit mutagenic properties. As KM-416 is a promising compound in our search for drug candidates, in the present study we further assessed its pharmacological profile (analgesic, local anesthetic, and antidepressant-like activities) accompanied with patch-clamp studies. Considering the importance of drug safety, its influence on the cardiovascular system was also evaluated. Moreover, KM-416 was subjected to forced degradation and pharmacokinetic studies to examine its stability and pharmacokinetic parameters. KM-416 revealed a significant antinociceptive activity in the tonic - the formalin test, neurogenic - the capsaicin test, and neuropathic pain model - streptozotocin-induced peripheral neuropathy. Moreover, it exerted a local anesthetic effect. In addition, KM-416 exhibited anti-depressant like activity. The results from the patch-clamp studies indicated that KM-416 can inhibit currents elicited by activation of NMDA receptors, while it also exhibited a voltage-dependent inhibition of Na⁺ currents. KM-416 did not influence ventricular depolarization and repolarization. Following oral administration, pharmacokinetics of KM-416 was characterized by a rapid absorption in the rat. The brain-to-plasma AUC ratio was 6.7, indicating that KM-416 was well distributed to brain. The forced degradation studies showed that KM-416 was very stable under stress conditions. All these features made KM-416 a promising drug candidate for further development against neuropathic pain and epilepsy.

Entrapping bupivacaine-loaded emulsions in a crosslinked-hydrogel increases anesthetic effect and duration in a rat sciatic nerve block model

The purpose of this research was to evaluate a novel long-acting bupivacaine delivery system for control of postoperative pain. Bupivacaine-loaded lipid emulsion (BLE) droplets were created by high-speed homogenization. The BLE droplets were then entrapped into a crosslinked-hyaluronic acid hydrogel system to create an injectable composite gel formulation (HA-BLE). Dynamic light scattering, rheological, and drug release techniques were used to characterize the formulations. A rat sciatic nerve block with a thermal nociceptive assay was used to evaluate the anesthetic effect in comparison to controls, bupivacaine HCl and liposomal bupivacaine. The BLE droplets had a zeta potential, droplet size, and polydispersity index of -40.8 ± 0.66 mV, 299 ± 1.77 nm, and 0.409 ± 0.037, respectively. The HA-BLE formulation could be injected through 25 g needles and had an elastic modulus of 372 ± 23.7 Pa. Approximately 80% and 100% of bupivacaine was released from the BLE and HA-BLE formulations by 20 and 68 h, respectively. The HA-BLE formulation had a 5-times greater anesthetic area under the curve and an anesthetic duration that was twice as long as controls. Results indicate that incorporating the BLEs into the hydrogel significantly increased anesthetic effect by protecting the BLE droplets from the in vivo environment.

Chlorpheniramine produces cutaneous analgesia in rats

BACKGROUND

This study sought to assess the cutaneous (peripheral) analgesic effects of antihistamine chlorpheniramine, compared with the long-lasting local anesthetic bupivacaine.

METHODS

After chlorpheniramine and bupivacaine were subcutaneously injected under the dorsal skin of the rats, the cutaneous analgesia effect was quantitatively evaluated by scoring the number to which the animal failed to react (cutaneous trunci muscle reflex). The quality and duration of chlorpheniramine and bupivacaine on infiltrative cutaneous analgesia were compared.

RESULTS

We revealed that subcutaneous chlorpheniramine, as well as the local anesthetic bupivacaine elicited cutaneous analgesia in a dosage-dependent manner. Based on their ED50s (50% effective doses), the relative potency was found to be chlorpheniramine [1.13 (1.05-1.22) μmol] < bupivacaine [0.52 (0.46-0.58) μmol] (p < 0.01). When comparing the ED25s, ED50s and ED75s, full recovery time induced by chlorpheniramine was longer (p < 0.01) than that induced by bupivacaine.

CONCLUSIONS

Our preclinical data demonstrated that both chlorpheniramine and bupivacaine dose-dependently provoked the cutaneous analgesic effects. Chlorpheniramine with a more prolonged duration was less potent than bupivacaine in inducing cutaneous analgesia.

Local anesthesia in piglets undergoing castration-A comparative study to investigate the analgesic effects of four local anesthetics on the basis of acute physiological responses and limb movements

Surgical castration of male piglets without analgesia is a painful procedure. This prospective, randomized and double-blinded study aimed to evaluate the analgesic effects of four different local anesthetics for piglet castration during the first week of life. In total, 54 piglets aged 3 to 7 days were distributed into 6 treatment groups: handling (H); castration without pain relief (sodium chloride, NaCl); and castration with a local anesthetic: 4% procaine (P), 2% lidocaine (L), 0.5% bupivacaine (B) or 20 mg/ml mepivacaine (M). By excluding stress and fear as disruptive factors via a minimum anesthesia model, all piglets received individual minimum alveolar concentration (MAC) isoflurane anesthesia. Twenty minutes before castration, all treatment groups except group H received one injection per testis. Then, 0.5 ml of a local anesthetic or NaCl was injected intratesticularly (i.t.), and 0.5 ml was administered subscrotally. Acute physiological responses to noxious stimuli at injection and castration were evaluated by measuring blood pressure (BP), heart rate (HR), cortisol, epinephrine, norepinephrine and chromogranin A (CgA); limb movements were quantified. The results confirm that castration without analgesia is highly painful. Surgical castration without pain relief revealed significant changes in mean arterial blood pressure (MAP) and HR. Local anesthetic administration significantly reduced changes in BP and HR associated with castration. Piglets receiving a preoperative local anesthetic exhibited the fewest limb movements during castration, while the NaCl group exhibited the most. Injection itself was not associated with significant changes in MAP or HR. However, many piglets exhibited limb movements during injection, indicating that the injection itself causes nociceptive pain. No significant differences were found between groups regarding parameters of plasma cortisol, catecholamines and CgA. In conclusion, all four local anesthetics administered are highly effective at reducing signs of nociception during castration under light isoflurane anesthesia. However, injection of a local anesthetic seems to be painful.

Chloroquine for prolonged skin analgesia in rats

The purpose of this study was to investigate the ability of chloroquine and chloroquine in combination with vasoconstrictor epinephrine to act as a local anesthetic in skin analgesia. After subcutaneous injection of drugs in rats, the inhibition of the cutaneous trunci muscle reflex (CTMR) is designed for evaluation of the cutaneous analgesic effect. The analgesic effect of chloroquine was compared with that of bupivacaine or coadministration of chloroquine and epinephrine. Chloroquine produced exactly the same local anesthesia as bupivacaine did in a dose-dependent manner. On the ED₅₀ (50 % effective dose) basis, the analgesic potency was chloroquine (4.81 [4.45-5.20] μmol) < bupivacaine (0.46 [0.40‒0.52] μmol) (p <  0.01). At every equipotent dose tested (ED₂₅, ED₅₀ and ED₇₅), chloroquine had a longer duration of cutaneous analgesia than bupivacaine (p <  0.01). Epinephrine enhanced the potency and duration of chloroquine-induced cutaneous analgesia. We found that chloroquine and bupivacaine elicit dose-dependent cutaneous analgesia. Chloroquine is not as potent as bupivacaine, but acts as an infiltrative anesthetic for a longer duration of time and is more potent and effective when used in combination with epinephrine.

Efficacy and duration of effect for liposomal bupivacaine when administered perineurally to the palmar digital nerves of horses

OBJECTIVE

To determine the efficacy and duration of effect for liposomal bupivacaine following perineural administration to the medial and lateral palmar digital nerves of horses.

ANIMALS

9 nonlame mares.

PROCEDURES

For each horse, 2 mL of liposomal bupivacaine (13.3 mg/mL; total dose, 53.2 mg or approx 0.11 mg/kg) or sterile saline (0.9% NaCl) solution was injected adjacent to the medial and lateral palmar digital nerves at the level of the distal aspect of the proximal sesamoid bones of a randomly selected forelimb. Twenty-one days later, the opposite treatment was administered in the contralateral forelimb. A digital algometer was used to measure the mechanical nociceptive threshold (MNT) immediately before and at predetermined times for 48 hours after injection of each treatment. The mean MNT was compared between the 2 treatments at each measurement time.

RESULTS

The mean MNT for the liposomal bupivacaine-treated limbs was significantly greater (ie, the limb was less sensitive) than that for the saline-treated limbs between 30 minutes and 4 hours after treatment injection. Following liposomal bupivacaine administration, 1 horse developed mild swelling at the injection sites that resolved without treatment within 24 hours. No other adverse effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that liposomal bupivacaine is another option for perineural anesthesia in horses. Further research is necessary to determine the optimal dose and better elucidate the duration of effect for the drug when used for palmar digital nerve blocks in horses.

Adjuncts to local anesthetic wound infiltration for postoperative analgesia: a systematic review

Local anesthetics (LAs) are commonly infiltrated into surgical wounds for postsurgical analgesia. While many adjuncts to LA agents have been studied, it is unclear which adjuncts are most effective for co-infiltration to improve and prolong analgesia. We performed a systematic review on adjuncts (excluding epinephrine) to local infiltrative anesthesia to determine their analgesic efficacy and opioid-sparing properties. Multiple databases were searched up to December 2019 for randomized controlled trials (RCTs) and two reviewers independently performed title/abstract screening and full-text review. Inclusion criteria were (1) adult surgical patients and (2) adjunct and LA agents infiltration into the surgical wound or subcutaneous tissue for postoperative analgesia. To focus on wound infiltration, studies on intra-articular, peri-tonsillar, or fascial plane infiltration were excluded. The primary outcome was reduction in postoperative opioid requirement. Secondary outcomes were time-to-first analgesic use, postoperative pain score, and any reported adverse effects. We screened 6670 citations, reviewed 126 full-text articles, and included 89 RCTs. Adjuncts included opioids, non-steroidal anti-inflammatory drugs, steroids, alpha-2 agonists, ketamine, magnesium, neosaxitoxin, and methylene blue. Alpha-2 agonists have the most evidence to support their use as adjuncts to LA infiltration. Fentanyl, ketorolac, dexamethasone, magnesium and several other agents show potential as adjuncts but require more evidence. Most studies support the safety of these agents. Our findings suggest benefits of several adjuncts to local infiltrative anesthesia for postoperative analgesia. Further well-powered RCTs are needed to compare various infiltration regimens and agents.

Protocol registration

PROSPERO (CRD42018103851) (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=103851)

Study on the Effect of Lidocaine in the Cuff for Endotracheal Tube in Vitro and in Vivo

OBJECTIVE

The purpose of this research was to investigate the effectiveness on postoperative pharyngalgia of filling the endotracheal catheter (ETC) cuffs with air, double distilled water, 2% lidocaine hydrochloride, and 1.73% lidocaine carbonate.

METHODS

A group of 80 female patients were divided into 4 groups randomly. The ETC cuffs were filled with air (Group A), double distilled water (Group B), 2% lidocaine hydrochloride (Group C), and 1.73% lidocaine carbonate (Group D) after endotracheal intubation in corresponding patients. Sore throat, hoarseness, bucking, perioperative hemodynamic changes were examined in all participants.

RESULTS

The Group D had significantly less severity of POST (P < 0.05), postoperative hoarseness (P < 0.05) and bucking on emergence from general anesthesia (P < 0.01) than patients from other groups. The Group D reported significantly less hemodynamic changes after extubation 1, 5, 10 minutes (P < 0.05).

CONCLUSION

Lidocaine carbonate injected into the ETC cuffs decreased the severity of postoperative pharyngalgia, postoperative hoarseness and bucking on emergence from general anesthesia.

Novel compound LL-a produces long and nociceptive-selective regional anesthesia via TRPV1 channels in rodents sciatic nerve block model

BACKGROUND AND OBJECTIVE

Long-acting nociceptive-selective regional anesthesia has remained an elusive clinical goal. We aspired to identify a novel compound that would produce nociceptive-selective regional anesthesia through the transient receptor potential vanilloid 1 (TRPV1) channels.

METHODS

We designed and synthesized a novel compound (LL-a) that penetrates the cell membrane through TRPV1 channels and binds to voltage-gated sodium channels. The regional anesthetic effect of LL-a was evaluated in a rodent sciatic nerve block model. Electrophysiological recording was applied to test the inhibition of LL-a on voltage-gated sodium channel currents.

RESULTS

LL-a inhibited sodium channel currents on the dorsal root ganglion neurons of mice and this action was diminished by TRPV1 channel knockout. In a sciatic nerve block model of a rat, 0.2% and 0.4% (w/v) LL-a produced selective sensory block with median (IQR) durations of 42.0 (24.0, 48.0) and 72.0 (69.0, 78.0) hours, respectively. No motor block was found for 0.2% LL-a. 0.4% LL-a produced a motor block with a median (IQR) duration of 3.0 (0.0, 6.0) hours. This selective sensory block was not observed on TRPV1 knockout mice. As a positive control, 0.5% and 0.75% levobupivacaine produced a non-selective sciatic nerve block with median (IQR) durations of 2.8 (2.6, 2.8) and 3.8 (3.8, 4.8) hours, respectively. No systemic or local irritation was observed during injection of LL-a and sensory and motor function completely recovered for all the animals.

CONCLUSIONS

LL-a is a potential novel local anesthetic for long-lasting nociceptive-selective analgesia.

Voltammetry of local anesthetics: theoretical and practical aspects

Local anesthetics (LAs) are widely used in anesthesiology, ophthalmology, and otolaryngology as well as for treatment of chronic and oncological pain. However, anesthetics can cause adverse effects up to lethal ones. In this work, we cited reviews on chromatographic and spectroscopic methods of local anesthetics determination published earlier, and the main purpose was to review the possibilities and advantages of voltammetric methods used for the LAs determination. The electrochemical behavior, mechanism of LAs transformation on the various working electrodes and analytical parameters of voltammetric methods used for their determination were reviewed in the work. Vast majority of these methods were developed for the most widely used anesthetics in medicine like benzocaine, lidocaine and procaine. Special attention was paid to possible mechanisms of electrochemical oxidation and in some cases reduction of LAs or their derivatives. Voltammetry is used for the determination of LAs in pharmaceutical formulations and in biological fluids. The analytical characteristics in terms of sensitivity, selectivity, reproducibility also were discussed in the article.

[Stocktaking of local anesthetics 2020]

For decades local anesthetics have proven to be safe and effective drugs in the clinical practice, crucially promoting the enormous achievements in regional anesthesia. Meanwhile, it is a well-known fact that local anesthetics are much more than just "simple" sodium channel blockers. They also interact with numerous other ion channels and subcellular structures, enhancing nerve blockade and resulting in systemic "alternative" effects, which can sometimes even be clinically used. By the simultaneous administration of various adjuvants (e.g., opioids, corticosteroids and α₂-receptor agonists) attempts are made to prolong the time of action of local anesthetics after a single administration in order to achieve the best possible improvement in postoperative analgesia. In this context, ultralong-acting local anesthetics, such as liposomal bupivacaine, which at least theoretically can provide a sensory nerve block for several days, have been developed and clinically introduced. The coming years will show whether these approaches will develop into genuine alternatives to the personnel and cost-intensive continuous nerve blockades.Local anesthetic-induced systemic toxicity is meanwhile rare but still a potentially life-threatening event, frequently resulting from accidental intravascular injection or extensive systemic resorption. Consequently, slow and fractional application of these agents with intermittent aspiration helps to prevent toxic sequelae. If toxic symptoms occur, however, the intravenous infusion of 20% lipid solutions in addition to basic treatment measures can enhance the success of treatment.

Contributions of natural products to ion channel pharmacology

Covering: Up to 2020Ion channels are a vast super-family of membrane proteins that play critical physiological roles in excitable and non-excitable cells. Their biomedical importance makes them valuable and attractive drug targets for neurological, cardiovascular, gastrointestinal and metabolic diseases, and for cancer therapy and immune modulation. Current therapeutics target only a minor subset of ion channels, leaving a large unexploited space within the ion channel field. Natural products harnessed from the almost unlimited and diverse universe of compounds within the bioenvironment have been used to modulate channels for decades. In this review we highlight the impact made by natural products on ion channel pharmacology, specifically on K⁺, Na_V and Ca_V channels, and use case studies to describe the development of ion channel-modulating drugs from natural sources for the treatment of pain, heart disease and autoimmune diseases.

Factors Associated With Minimum Effective Volume of Lidocaine 1.5% for Sciatic Nerve Blocks

OBJECTIVES

The objectives of this study were to investigate the correlations between the minimum effective volume (MEV) of lidocaine 1.5% for an ultrasound-guided popliteal sciatic nerve block and individual factors including the cross-sectional nerve area, sex, age, body mass index, and the depth of the sciatic nerve and to evaluate the safety of combined femoral and sciatic nerve blocks by monitoring the plasma concentration of local anesthetics.

METHODS

Forty patients received combined single-shot femoral and continuous sciatic nerve blocks. The femoral nerve block was performed with an in-plane technique and 15 mL of lidocaine 1.5%. A continuous peripheral nerve block annular tube was positioned between the tibial and peroneal nerves inside the paraneural sheath. Thirty minutes after the femoral nerve block, a loading dose of 5 mL of lidocaine 1.5% was given to block the sciatic nerve after obtaining the maximum compound muscle action potential (CMAP) amplitude using nerve conduction studies. Additional lidocaine 1.5% was pumped at a rate of 30 mL/h through the indwelling annular tube if, after 8 minutes, the CMAP amplitude was still present. The CMAP amplitude monitored by the nerve conduction studies and pinprick tests were recorded every 2 minutes after the administration of lidocaine 1.5%. When the CMAP amplitude decreased to nearly 0 mV, this MEV was recorded. The influences of the cross-sectional area of the sciatic nerve, sex, age, body mass index, and the depth of the sciatic nerve on the MEV were analyzed using stepwise multiple linear regression. Blood samples were collected from 10 patients to evaluate the safety of combined femoral and sciatic nerve blocks by ultra-performance liquid chromatography-tandem mass spectrometry. Blood was drawn at 0 minutes before femoral nerve injection; 0 minutes before sciatic nerve injection; 8 minutes after sciatic nerve injection; and 0, 10, 20, 30, 45, 60, 75, 90, and 120 minutes after the pumping of lidocaine 1.5% stopped.

RESULTS

A significant correlation was found between the MEV of lidocaine 1.5% and the cross-sectional area of the sciatic nerve (r=0.459), with a regression equation of the MEV (mL)=5.969+0.095×(the cross-sectional area of the sciatic nerve). The coefficient of determination was 0.211 (P<0.05). The MEV of lidocaine 1.5% for complete sciatic nerve blocks ranged from 7 to 15 mL. The maximum concentrations of lidocaine, monoethylglycinexylidide, and glycinexylidide were 1672.9 (227.6), 265.7 (32.7), and 42.2 (22.4) ng/mL, respectively.

CONCLUSIONS

There is a positive correlation between the cross-sectional area of the sciatic nerve and the MEV. The regression equation can help to predict the MEV of lidocaine 1.5% for popliteal sciatic nerve blocks. The maximum concentrations of lidocaine and its metabolites did not approach toxic threshold limits in this study.

Subcutaneous brompheniramine for cutaneous analgesia in rats

Brompheniramine as an antihistamine blocked sodium channels, and local anesthetics by blocking sodium channels produced the local anesthetic effects. The authors aimed to assess local anesthetic quality and duration of brompheniramine when compared to the local anesthetic mepivacaine. After rats were shaved and injected subcutaneously on the dorsal skin, the panniculus reflex, induced via applying a noxious pinprick to the skin (injected area), was scored. The dose-response curve and nociceptive block duration of brompheniramine were constructed and compared with mepivacaine. The cutaneous analgesic effects in both brompheniramine and mepivacaine groups were concentration-dependent. On the basis of the amount required to produce a 50% block effect (ED50, 50% effective dose), the drug's potency was brompheniramine (0.89 [0.82-0.96] μmol) better than mepivacaine (2.45 [2.17-2.76] μmol) (P < 0.01). Full recovery time of brompheniramine was more prolonged than mepivacaine's (P < 0.01) on infiltrative cutaneous analgesia when comparing ED25s, ED50s and ED75s. Our preclinical data demonstrated that subcutaneous brompheniramine induces dose-relatedly analgesic effects, and brompheniramine induces prolonged analgesic duration when compared with mepivacaine. Brompheniramine also provokes better cutaneous analgesia than mepivacaine.

Dopamine enhancement of dextrorphan-induced skin antinociception in response to needle pinpricks in rats

BACKGROUND

Dextrorphan with long-acting local anesthetic effects did not cause system toxicity as fast as bupivacaine, while catecholamines (i.e., epinephrine) with the vasoconstrictive characteristics enhanced the effects of local anesthetic drugs. The objective of the experiment was to examine the synergistic effect of local dopamine (a catecholamine) injection on cutaneous antinociception of dextrorphan.

METHODS

The panniculus reflex in response to skin stimulation with a needle was used as the primary endpoint when dextrorphan (1.50, 2.61, 5.46, 10.20 and 20.40 μmol) alone, dopamine (16.20, 32.40, 51.60, 60.00 and 81.60 μmol) alone, or dopamine + dextrorphan (a ratio of ED50vs. ED50) was injected subcutaneously on the rat's back. We used an isobolographic modelling approach to determine whether a synergistic effect would be observed.

RESULTS

We showed that dextrorphan, dopamine, or the mixture of dopamine and dextrorphan produced dose-related skin antinociception. The potency (ED50, 50% effective dose) for cutaneous antinociception was dextrorphan [6.02 (5.93-6.14) μmol] greater than dopamine [48.91 (48.80-49.06) μmol] (p < 0.01). The duration of nociceptive inhibition induced by dopamine was longer than that induced by dextrorphan (p <  0.01) based on their equipotent doses (ED25, ED50, and ED75). Enhancement and prolongation of skin antinociception occurred after co-administration of dopamine with dextrorphan.

CONCLUSIONS

When compared to dopamine, dextrorphan was more potent and had a shorter duration of skin nociceptive block. Dopamine produced a synergistic effect on dextrorphan-mediated antinociception, and prolonged dextrorphan's antinociceptive duration.