Population Pharmacokinetics of Intravenous Lidocaine in Adults: A Systematic Review.

BACKGROUND: The establishment of optimal dosing regimens for intravenous (IV) lidocaine in the perioperative setting, aiming to balance effective pain relief with minimisation of potential side effects, is a topic of ongoing debate. This discussion stems from the significant variability in lidocaine's pharmacokinetic (PK) parameters and its relatively narrow safety margin. Population pharmacokinetic (popPK) modelling has emerged as a valuable tool for understanding the factors contributing to this observed variability in drug kinetics. OBJECTIVES: This systematic review compiles the existing knowledge on lidocaine's PK properties and published popPK models, with a focus on significant covariates. METHODS: A systematic search on Cochrane CENTRAL, Medline, and EMBASE was performed from inception to June 2023. Original clinical studies that administered IV lidocaine to adults and performed PK analyses using a nonlinear mixed effects modelling approach were included. The quality of the included studies was assessed by compliance with the Clinical Pharmacokinetics (ClinPK) statement checklist. RESULTS: Seven studies were included, which involved a diverse adult population, including both volunteers and patients with various comorbidities. Lidocaine PK was primarily characterised by a two- or three-compartment model. The volume of distribution at steady state ranged from 66 to 194 L, and the total clearance ranged from 22 to 49 L/h. Despite adjusting for significant covariates like heart failure status, alpha-1-acid glycoprotein, duration of lidocaine infusion, and body weight, each study revealed substantial variability in PK parameters. The potential impact of hepatic or renal function biomarkers on these PK parameters calls for further investigation. Incomplete reporting of key aspects of developed models may hinder the models' reliability and clinical application. CONCLUSION: The findings emphasise the importance of tailoring drug dosage to ensure the safe and effective use of intravenous lidocaine. Optimal design methodologies may be incorporated for a more efficient identification of important covariates. Utilising contemporary model evaluation methods like visual predictive checks and bootstrapping would enhance the robustness of popPK models and the reliability of their predictions. This comprehensive review advances our understanding of lidocaine's pharmacokinetics and lays the groundwork for further research in this critical area of perioperative pain management. Review protocol registered on 25 August 2023 in PROSPERO (CRD42023441113). This work was supported by the Fundamental Research Grant Scheme, the Ministry of Higher Education, Malaysia (FRGS/1/2020/SKK01/UM/02/2).

Absorption and pharmacokinetics of bupivacaine after bilateral topical administration in tonsillar fossae for posttonsillectomy pain relief.

No previous studies have investigated the systemic absorption of bupivacaine when used topically for posttonsillectomy pain. The present study was undertaken to investigate the pharmacokinetics of bupivacaine after administration by a swab in the tonsillar fossae over 4 min after tonsillectomy. Eleven adult patients undergoing elective tonsillectomy were recruited. After removal of both tonsils, each of the two tonsillar fossae was covered with a swab moistened with 2 mL of bupivacaine 5 mg/mL, that is, a total of 20 mg bupivacaine. Blood samples were drawn after 0, 5, 10, 20, 30, 45, and 60 min. Bupivacaine was analyzed with an ultra-high-performance liquid chromatography-tandem mass spectrometry method. The highest single measured bupivacaine serum concentration was 23.2 ng/mL and took place 10 min after drug administration. Mean (±SD) Cmax was 11.4 ± 6.0 ng/mL and mean tmax was 11.3 ± 4.7 min. Mean t1/2 was 31.6 ± 9.3 min. As the toxic concentration threshold has been reported to be in the interval 1500-4500 ng/mL, the concentrations measured were well below 2% of the lowest cited toxic threshold. In conclusion, this study shows that applying 4 mL of bupivacaine 5 mg/mL by a swab in the tonsillar fossae posttonsillectomy yields very low plasma concentrations, suggesting its safe application without any risk of systemic toxic effects.

Blood bupivacaine concentrations after pecto-serratus and serratus anterior plane injections of plain and liposomal bupivacaine in robotically-assisted mitral valve surgery: Sub-study of a randomized trial.

STUDY OBJECTIVE: To investigate the timing of peak blood concentrations and potential toxicity when using a combination of plain and liposomal bupivacaine for thoracic fascial plane blocks. DESIGN: Pharmacokinetic analysis. SETTING: Operating room. PATIENTS: Eighteen adult patients undergoing robotically-assisted mitral valve surgery. INTERVENTIONS: Ultrasound-guided pecto-serratus and serratus anterior plane blocks using a mixture of 0.5% bupivacaine HCl up to 2.5 mg/kg and liposomal bupivacaine up to 266 mg. MEASUREMENTS: Arterial plasma bupivacaine concentration. MAIN RESULTS: Samples from 13 participants were analyzed. There was substantial inter-patient variability in plasma concentrations. A geometric mean maximum bupivacaine concentration was 1492 ng/ml (range 660 to 4650 ng/ml) at median time of 30 min after injection. In 4/13 (31%) patients, plasma bupivacaine concentrations exceeded our predefined 2000 ng/ml toxic threshold. A second much smaller peak was observed about 32 h after the injection. No obvious signs of local anesthetic toxicity were observed. CONCLUSIONS: Combined injection of plain and liposomal bupivacaine for pecto-serratus/serratus anterior plane blocks produced a biphasic pattern, with the highest arterial plasma concentrations observed within 30 min. Maximum concentrations exceeded the potential toxic threshold in nearly a third of patients, but without clinical evidence of toxicity. Clinicians should not assume that routine combinations of plain and liposomal bupivacaine for thoracic fascial plane blocks are inherently safe.

Assessment of Total Ropivacaine Concentration in Blood after Bilateral Pecto-Intercostal Fascial Block Combined with Rectus Sheath Block in Cardiac Surgery Patients.

OBJECTIVES: Pecto-intercostal fascial block (PIFB) and rectus sheath block (RSB) have been combined to offer better analgesia for cardiac surgery patients, but safety of the analgesic protocol with a large volume of ropivacaine is uncertain. METHODS: This is a prospective observational study at Peking University People's Hospital to investigate the pharmacokinetic profile of ropivacaine after combined regional blocks. Patients undergoing elective cardiac surgery by a median sternotomy were enrolled to receive bilateral PIFB and RSB with 70 mL 0.3% ropivacaine (total dose 210 mg). Blood was sampled at 5, 10, 15, 30, 60, 90 and 120 mins after blocks. Total blood concentration of ropivacaine for patients were measured. RESULTS: Ten patients were enrolled and analyzed. The peak total ropivacaine concentration varied from 0.67 to 2.42 µg/mL. Time to reach the peak values mainly located between 10 and 30 mins after the performance. No patients had ropivacaine concentration values above toxic threshold (4.3 µg/mL), and there were no systemic toxicity symptoms during the perioperative period. CONCLUSIONS: PIFB combined with RSB in a general injection of 70 mL 0.3% ropivacaine does not give rise to toxic levels, and it is an effective and safe analgesic protocol for cardiac surgery patients.

Micro-pharmacokinetics of lidocaine and bupivacaine transfer across a myelinated nerve fiber.

BACKGROUND: The aim of the present study was to predict the time to onset and duration of action of two local anesthetics (lidocaine and bupivacaine) based on experimental dimensions of a typical nerve and experimental octanol/water partition coefficients. METHODS: We began our compilation of experimental data with a numerical solution of the Smoluchowski equation for the transfer of lidocaine and bupivacaine across the axon membrane in the region of the node of Ranvier (axolemma) and across the Schwann cell. The difference between the aqueous and lipid environments of the neuron was simulated by including the coordinate-dependent chemical potential. In the second step, the permeation rates calculated using the diffusion equation were used to solve a system of four ordinary differential equations. This approach allowed us to simulate the cellular environment for a longer time and to compare our model with pharmacokinetic properties (time to onset and duration of action) of local anesthetics from the literature. The behavior of local anesthetics under physiological conditions and in case of local acidosis was also simulated. RESULTS: We demonstrated that local anesthetics cross the axolemma in a time span of less than 1 µs. The time to onset of action, controlled by diffusion from the epineurium to an axon with a typical distance of 500 µm, was 167 s and 186 s for lidocaine and bupivacaine, respectively. The calculated half-life, which is a measure of the duration of action, was 41 min and 328 min for lidocaine and bupivacaine, respectively. CONCLUSIONS: Duration of action is controlled by the storage capacity of lipophilic compartments around the axon, which is higher for bupivacaine but lower in local acidosis. For the latter case, the literature, including textbooks, provides a misinterpretation, namely that protonated species cannot penetrate the membrane.

Plasma concentrations of levobupivacaine in neonates during caudal epidural analgesia maintained over 48 hours.

BACKGROUND: Differences in neonatal pharmacokinetics are known to cause systemic accumulation of levobupivacaine with adverse effects during epidural analgesia. Therefore, it is not recommended to surpass 48 hours of administration in neonates. Free and total levobupivacaine levels are considered as predictors of toxicity. OBJECTIVE: The aim of the LEVON pilot study was to detect the accumulation of levobupivacaine during epidural analgesia exceeding 48 hours in neonates. METHODS: Ten neonates received a loading dose of levobupivacaine (1.25 mg/kg) followed by a continuous infusion (0.2 mg/kg/hour) epidurally. Free and total levobupivacaine concentrations were measured 0.5, 1, 6, 12, 36, 72 and 144 hours after the start of infusion. Cumulative doses of levobupivacaine, pain scores and clinical signs of toxicity were used for assessing efficacy and safety. RESULTS: The median concentrations of total levobupivacaine were 586.0, 563.0, 837.5, 957.0, 1930.0, 708.5 and 357.5 ng/ml. The median concentrations of free levobupivacaine were 4.0, 3.6, 5.5, 3.6, 5.5, 0.8 and 0.0 ng/ml. Three patients reached concerning concentrations of total levobupivacaine. Levels of free levobupivacaine remained low. No signs of toxicity were observed. CONCLUSION: Caudal epidural analgesia with levobupivacaine lasting longer than 48 hours appears to be safe providing that free levobupivacaine levels are below the presumed threshold for toxicity (Tab. 1, Fig. 1, Ref. 29). Text in PDF www.elis.sk Keywords: free levobupivacaine, total levobupivacaine, neonate, caudal continuous epidural analgesia, postoperative pain.

Synthesis of nanocapsules blended polymeric hydrogel loaded with bupivacaine drug delivery system for local anesthetics and pain management.

Local anesthetics are used clinically for the control of postoperative pain management. This study aimed to develop chitosan (CS) with genipin (GP) hydrogels as the hydrophilic lipid shell loaded poly(ε-caprolactone) (PC) nanocapsules as the hydrophobic polymeric core composites (CS-GP/PC) to deliver bupivacaine (BPV) for the prolongation of anesthesia and pain relief. The swelling ratio, in vitro degradation, and rheological properties enhancement of CS-GP/PC polymeric hydrogel. The incorporation of PC nanocapsules into CS-GP hydrogels was confirmed by SEM, FTIR, and XRD analysis. Scanning electron microscopy results demonstrated that the CS-GP hydrogels and CS-GP/PC polymeric hydrogels have a porous structure, the pore dimensions being non-uniform with diameters between 25 and 300 µm. The in vitro drug release profile of CS-GP/PC polymeric hydrogel has been achieved 99.2 ± 1.12% of BPV drug release in 36 h. Cellular viability was evaluated using the CCK-8 test on 3T3 fibroblast cells revealed that the obtained CS-GP/PC polymeric hydrogel with BPV exhibited no obvious cytotoxicity. The CS-GP/PC polymeric hydrogel loaded with BPV showed significant improvement in pain response compared to the control group animals for at least 7 days. When compared with BPV solution, CS-GP hydrogel and CS-GP/PC polymeric hydrogel improved the skin permeation of BPV 3-fold and 5-fold in 24 h, respectively. In vitro and in vivo results pointed out PC nanocapsules loaded CS-GP hydrogel can act as effective drug carriers, thus prolonging and enhancing the anesthetic effect of BPV. Histopathological results demonstrated the excellent biodegradability and biocompatibility of the BPV-loaded CS-GP/PC polymeric hydrogel system on 7, 14, and 21 days without neurotoxicity.HIGHLIGHTSPreparation and characterization of CS-GP/PC polymeric hydrogel system.BPV-loaded CS-GP/PC exhibited prolonged in vitro release in PBS solution.Cytotoxicity of BPV-loaded CS-GP/PC polymeric hydrogel against fibroblast (3T3) cells.Development of CS-GP/PC a promising skin drug-delivery system for local anesthetic BPV.

Pharmacological and clinical implications of local anaesthetic mixtures: a narrative review.

Various techniques have been explored to prolong the duration and improve the efficacy of local anaesthetic nerve blocks. Some of these involve mixing local anaesthetics or adding adjuncts. We did a literature review of studies published between 01 May 2011 and 01 May 2021 that studied specific combinations of local anaesthetics and adjuncts. The rationale behind mixing long- and short-acting local anaesthetics to hasten onset and extend duration is flawed on pharmacokinetic principles. Most local anaesthetic adjuncts are not licensed for use in this manner and the consequences of untested admixtures and adjuncts range from making the solution ineffective to potential harm. Pharmaceutical compatibility needs to be established before administration. The compatibility of drugs from the same class cannot be inferred and each admixture requires individual review. Precipitation on mixing (steroids, non-steroidal anti-inflammatory drugs) and subsequent embolisation can lead to serious adverse events, although these are rare. The additive itself or its preservative can have neurotoxic (adrenaline, midazolam) and/or chondrotoxic properties (non-steroidal anti-inflammatory drugs). The prolongation of block may occur at the expense of motor block quality (ketamine) or block onset (magnesium). Adverse effects for some adjuncts appear to be dose-dependent and recommendations concerning optimal dosing are lacking. An important confounding factor is whether studies used systemic administration of the adjunct as a control to accurately identify an additional benefit of perineural administration. The challenge of how best to prolong block duration while minimising adverse events remains a topic of interest with further research required.

The impact of height on the spread of spinal anesthesia and stress response in parturients undergoing caesarean section: a prospective observational study.

BACKGROUND: The spread of spinal anesthesia was influenced by many factors, and the effect of body height on spinal anesthesia is still arguable. This study aimed to explore the impact of height on the spread of spinal anesthesia and the stress response in parturients. METHODS: A total of ninety-seven parturients were allocated into two groups according to their height: the shorter group (body height was shorter than 158 cm) and taller group (body height was taller than 165 cm). Spinal anesthesia was performed with the same amount of 12 mg plain ropivacaine in mothers of different heights. The primary outcome of the study was the success or failure of the spinal anesthesia. The secondary outcomes of the study were stress response, time to T6 sensory level, the incidence of hypotension, the satisfaction of abdominal muscle relaxation and patient VAS scores. RESULTS: The rate of successful spinal anesthesia in the shorter group was significantly higher than that in the taller group (p = 0.02). The increase of maternal cortisol level in the shorter group was lower than that in the taller group at skin closure (p = 0.001). The incidence of hypotension (p = 0.013), time to T6 sensory block (p = 0.005), the quality of abdominal muscle relaxation (p <  0.001), and VAS values in stretching abdominal muscles and uterine exteriorization (p <  0.001) in the shorter group were significantly different from those in the taller group. Multivariate analysis showed that vertebral column length (p <  0.001), abdominal girth (p = 0.022), amniotic fluid index (p = 0.022) were significantly associated with successful spinal anesthesia. CONCLUSIONS: It's difficult to use a single factor to predict the spread of spinal anesthesia. Patient's vertebral column length, amniotic fluid index and abdominal girth were the high determinant factors for predicting the spread of spinal anesthesia. TRIALS REGISTRATION: ChiCTR-ROC-17012030 ( Chictr.org.cn ), registered on 18/07/2017.

Pharmacokinetics and safety of liposomal bupivacaine after local infiltration in healthy Chinese adults: a phase 1 study.

BACKGROUND: Liposomal bupivacaine (LB) is a long-acting formulation of bupivacaine. The safety and efficacy of LB has been demonstrated across surgical procedures. However, pharmacokinetic (PK) parameters and safety of LB in the Chinese population have not been assessed. METHODS: In this single-arm, single center, phase 1, open-label study, PK and safety of local infiltration with LB 266 mg were assessed in healthy Chinese adults. Eligible participants were aged 18 to 55 years with biologic parents and grandparents of Chinese ethnicity, in generally good health (i.e., no clinically significant abnormalities), and with a body mass index (BMI) 19.0 to 24.0 kg/m2 (inclusive) and body weight ≥ 50 kg. RESULTS: Participants (N = 20) were predominantly men (80 %); mean age was 32 years; and mean BMI was 21.8 kg/m2. After LB administration, mean plasma levels of bupivacaine rapidly increased during the first hour and continued to increase through 24 h; plasma levels then gradually decreased through 108 h followed by a monoexponential decrease through 312 h. Geometric mean maximum plasma concentration was 170.9 ng/mL; the highest plasma bupivacaine concentration detected in any participant was 374.0 ng/mL. Twenty-two treatment-emergent adverse events were reported (mild, n = 21; moderate, n = 1). CONCLUSIONS: After single-dose administration of LB, PK measures were similar to a previously reported profile in US adults. The highest observed peak plasma concentration of bupivacaine was several-fold below the plasma concentration threshold accepted as being associated with neurotoxicity or cardiotoxicity (2000-4000 ng/mL). These data support that LB is well tolerated and safe in individuals of Chinese descent. TRIAL REGISTRATION: NCT04158102 (ClinicalTrials.gov identifier), Date of registration: November 5, 2019.

Formulation optimization, anesthetic activity, skin permeation, and transportation pathway of Alpinia galanga oil SNEDDS in zebrafish (Danio rerio).

Alpinia galanga oil (AGO) has an anesthetic activity but its water insoluble property limits its clinical applications. The aim of the present study was to develop a self-nanoemulsifying drug delivery system of AGO (SNEDDS-AGO) to avoid the use of organic solvent and investigate AGO transportation pathway and anesthetic activity. Three optimized formulations from a contour plots of droplet size; SNEDDS-AGO-1, SNEDDS-AGO-2, and SNEDDS-AGO-3, composed of AGO, Miglyol 812, Cremophor RH 40, Capmul MCM EP, and ethanol at the ratios of 40:10:35:10:5, 40:20:15:20:5, and 60:10:15:10:5, respectively were selected as they possessed different droplet size of 62 ± 0.5, 107 ± 2.8, and 207 ± 4.3 nm, respectively. It was found that the droplet size played an important role in fish anesthesia. SNEDDS-AGO-3 showed the longest anesthetic induction time (270 sec) (p < 0.03). Transportation pathway and skin permeation of SNEDDS-AGO-2 were investigated using nile red labelled AGO and detected by fluorescence microscope. AGO was found mostly in brain, gills, and skin suggesting that the transportation pathway of AGO in zebrafish is passing through the gills and skin to the brain. SNEDDS-AGO formulations showed significantly higher permeation through the skin than AGO ethanolic solution. In conclusion, SNEDDS is a promising delivery system of AGO.

Impact of Different Mixing Methods on the Performance of Suspension-Based Transdermal Delivery Systems.

Suspension-based matrix transdermal delivery systems (TDSs) are specialized systems that maintain a continuous driving force for drug delivery over prolonged wear. The pressure-sensitive adhesive (PSA) is the most critical constituent of such systems. Our study aimed to determine the effect of different mixing methods on the performance of silicone PSA-based suspension TDSs. Lidocaine suspension TDSs were prepared using conventional slow rotary mixing, high-speed homogenization, bead-mill homogenization, vortex shaking, and by an unguator. Resultant TDSs were tested for tack, shear, and peel properties and correlated to coat weight, content uniformity, microstructure, and in vitro permeation across dermatomed human skin. Every mixing method tested caused a significant reduction in peel. However, bead-mill homogenization resulted in significant loss of all adhesive properties tested, while unguator-mixed TDSs retained most properties. Good linear correlation (R2 = 1.000) between the shear properties of the TDSs with the average cumulative amount of lidocaine permeated after 24 h was observed, with no significant difference between percutaneous delivery from slow rotary-mixed systems (1334 ± 59.21 µg/cm2) and unguator-mixed systems (1147 ± 108.3 µg/cm2). However, significantly lower delivery from bead-mill homogenized systems (821.1 ± 28.00 µg/cm2) was noted. While many factors affect TDS performance, careful consideration must also be given to the processing parameters during development as they have been shown to affect the resultant system's therapeutic efficacy. Extensive mixing with bead-mill homogenization demonstrated crystallization of drug, loss in adhesive properties, coat weight, and film thickness, with reduced transdermal delivery of lidocaine from the prepared system.

Topical anesthetic and pain relief using penetration enhancer and transcriptional transactivator peptide multi-decorated nanostructured lipid carriers.

Many strategies have been developed to overcome the stratum corneum (SC) barrier, including functionalized nanostructures. Chemical penetration enhancers (CPEs) and cell-penetrating peptides (CPP) were applied to decorate nanostructured lipid carriers (NLC) for topical anesthetic and pain relief. A novel pyrenebutyrate (PB-PEG-DSPE) compound was synthesized by the amide action of the carboxylic acid group of PB with the amido groups of DSPE-PEG. PB-PEG-DSPE has a hydrophobic group, hydrophilic group, and lipid group. The lipid group can be inserted into NLC to form PB functional NLC. In order to improve the penetrability, TAT and PB multi-decorated NLC were designed for the delivery of lidocaine hydrochloride (LID) (TAT/PB LID NLC). The therapeutic effects of NLC in terms of in vitro skin penetration and in vivo in animal models were further studied. The size of TAT/PB LID NLC tested by DLS was 153.6 ± 4.3 nm. However, the size of undecorated LID NLC was 115.3 ± 3.6 nm. The PDI values of NLC vary from 0.13 ± 0.01 to 0.16 ± 0.03. Zeta potentials of NLC were negative, between -20.7 and -29.3 mV. TAT/PB LID NLC (851.2 ± 25.3 µg/cm2) showed remarkably better percutaneous penetration ability than PB LID NLC (610.7 ± 22.1 µg/cm2), TAT LID NLC (551.9 ± 21.8 µg/cm2) (p < .05) and non-modified LID NLC (428.2 ± 21.4 µg/cm2). TAT/PB LID NLC exhibited the most prominent anesthetic effect than single ligand decorated or undecorated LID NLC in vivo. The resulting TAT/PB LID NLC exhibited good skin penetration and anesthetic efficiency, which could be applied as a promising anesthesia system.

Spinal anaesthesia with Chloroprocaine HCl 1% for elective lower limb procedures of short duration: a prospective, randomised, observer-blind study in adult patients.

BACKGROUND: This prospective, randomised, observer-blinded study has been conducted in patients undergoing procedures of the lower extremities to evaluate the time to complete block resolution of 2-chloroprocaine 1% at three intrathecal doses (30, 40 and 50 mg). METHODS: After informed consent, we enrolled 45 male and female patients, aged 18-65 years, ASA score I-II, BMI 18-32 kg/m2, undergoing elective lower limb procedures lasting ≤40 min and with a requested dermatomeric level of sensory block ≥ T12. The patients were randomised in a 1:1:1 ratio to receive Chloroprocaine HCl 1% at one of the three different intrathecal doses (Group 30 = 30 mg, Group 40 = 40 mg or Group 50 = 50 mg). The progression and regression of both sensory and motor blocks were evaluated blindly. Urine and venous blood samples were collected for pharmacokinetic analysis. RESULTS: Times to regression of spinal blocks were 1.76 ± 0.35 h, 2.13 ± 0.46 h and 2.23 ± 0.38 h, in Group 30, 40 and 50 respectively: the 30 mg dose showed a significantly faster resolution of spinal block than the 40 mg (p = 0.034) and the 50 mg (p = 0.006). Time to readiness for surgery was significantly reduced with the dose of 50 mg when compared to dose of 30 mg (p = 0.0259). CONCLUSIONS: The doses of 50 mg and 40 mg yielded a longer resolution of spinal block than the dose of 30 mg. Nevertheless, the dose of 30 mg resulted in a higher secondary failure rate. TRIAL REGISTRATION: Registration of clinical trial: clinicaltrials.gov ( NCT02481505 ).

Novel insights on the encapsulation mechanism of PLGA terminal groups on ropivacaine.

Currently, the influences of free terminal groups (hydroxyl, carboxyl and ester) of PLGA on encapsulating active pharmaceutical ingredient are relatively ambiguous even though PLGA types were defined as critical quality attributes in vast majority of design of experiment process. In this study, emulsion method combined with premix membrane emulsification technique has been used to encapsulate ropivacaine (RVC), a small molecule local anesthetic in clinical. Based on the narrow particle size distribution, the influences and mechanisms of the terminal groups on properties of ropivacaine loaded microspheres have been investigated in detail. It was found that microspheres prepared by PLGA with hydroxyl or ester groups exhibited lower encapsulation efficiency but faster in vitro release rate than that of carboxyl groups. In the meanwhile, on microcosmic level analysis by quartz crystal microbalance with dissipation, atomic force microscope and confocal laser scanning microscopy, we attributed this distinction to the specific interaction between ropivacaine and different terminal groups. Subsequently, the reaction activation centers were verified by density functional simulation calculation and frontier molecular orbital theory at molecular level. Additionally, pharmacokinetics and pharmacodynamic research of infiltration anesthesia model were performed to compare sustained release ability, duration and intensity of the anesthetic effect in vivo. Finally, potential safety and toxicity were evaluated by the biochemical analysis. This study not only provides a novel mechanism of drug encapsulation process but also potential flexible selections in terms of various anesthesia indications in clinical.

Quantification of systemic o-toluidine after intrathecal administration of hyperbaric prilocaine in humans: a prospective cohort study.

Hyperbaric 2% prilocaine is increasingly used for spinal anesthesia. It is the only local anesthetic metabolized to o-toluidine, a human bladder carcinogen. Increase of o-toluidine hemoglobin adducts, a marker of o-toluidine ability to modify the DNA structure, was described following subcutaneous injection. In this prospective cohort study we aimed to assess and quantify o-toluidine hemoglobin adducts and urinary o-toluidine after a single intrathecal dose of hyperbaric prilocaine.10 patients undergoing surgery received 50 mg of hyperbaric prilocaine intrathecally. Blood and urine samples were collected before injection and up to 24 h later (Hospital Braine l'Alleud-Waterloo, Braine l'Alleud, Belgium). Urinary o-toluidine and o-toluidine hemoglobin adducts were measured by tandem mass-spectrometry after gas-chromatographic separation (Institute of the Ruhr-Universität, Bochum Germany). The trial was registered to ClinicalTrials.gov (NCT03642301; 22-08-2018)Intrathecal administration of 50 mg of hyperbaric prilocaine leads to a significant increase of o-toluidine hemoglobin adducts (0.1 ± 0.02-11.9 ± 1.9 ng/g Hb after 24 h, p = 0.001). Peak of urinary o-toluidine was observed after 8 h (0.1 ± 0.1-460.5 ± 352.8 µg/L, p = 0.001) and declined to 98 ± 66.8 µg/L after 24 h (mean ± SD)Single intrathecal administration of hyperbaric prilocaine leads to a systemic burden with o-toluidine and o-toluidine hemoglobin adducts. O-toluidine-induced modifications of DNA should be examined and intrathecal hyperbaric prilocaine should not be proposed to patients chronically exposed to o-toluidine.Clinical trial number and registry URL NCT03642301.

Population pharmacokinetics of ropivacaine used for local infiltration anaesthesia during primary total unilateral and simultaneous bilateral knee arthroplasty.

BACKGROUND: Ropivacaine is commonly used in local infiltration anaesthesia (LIA) as pain management after total knee arthroplasty (TKA). Although considered safe, no studies evaluated the pharmacokinetics of high-dose ropivacaine infiltration in simultaneous bilateral TKA. METHODS: We studied 13 patients undergoing unilateral and 15 undergoing bilateral TKA. Standard LIA technique was used with ropivacaine 0.2%, 200 ml (400 mg) injected peri-articularly in each knee. Free and total plasma concentrations of ropivacaine were measured within 24 h using liquid chromatography-mass spectrometry. A population pharmacokinetic model was built using non-linear mixed-effects models. RESULTS: Peak free ropivacaine concentration was 0.030 (0.017-0.071) µg ml-1 (mean [99% confidence interval]) vs 0.095 (0.047-0.208) µg ml-1, and peak total ropivacaine concentration was 0.756 (0.065-1.222) µg ml-1vs 1.695 (0.077-3.005) µg ml-1 for unilateral and bilateral TKA, respectively. The pharmacokinetics was ascribed a one-compartment model with first-order absorption. The main identified covariates were protein binding, allometrically scaled body weight on clearance and volume, and unilateral or bilateral surgery on volume. CONCLUSIONS: This is the first study to investigate the pharmacokinetics of free and total ropivacaine after unilateral and bilateral TKA. A population model was successfully built and peak free ropivacaine concentration stayed below previously proposed toxic thresholds in patients undergoing unilateral and bilateral TKA receiving LIA with high-dose ropivacaine. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04702282.

A weight of evidence assessment of the genotoxicity of 2,6-xylidine based on existing and new data, with relevance to safety of lidocaine exposure.

Lidocaine has not been associated with cancer in humans despite 8 decades of therapeutic use. Its metabolite, 2,6-xylidine, is a rat carcinogen, believed to induce genotoxicity via N-hydroxylation and DNA adduct formation, a non-threshold mechanism of action. To better understand this dichotomy, we review literature pertaining to metabolic activation and genotoxicity of 2,6-xylidine, identifying that it appears resistant to N-hydroxylation and instead metabolises almost exclusively to DMAP (an aminophenol). At high exposures (sufficient to saturate phase 2 metabolism), this may undergo metabolic threshold-dependent activation to a quinone-imine with potential to redox cycle producing ROS, inducing cytotoxicity and genotoxicity. A new rat study found no evidence of genotoxicity in vivo based on micronuclei in bone marrow, comets in nasal tissue or female liver, despite high level exposure to 2,6-xylidine (including metabolites). In male liver, weak dose-related comet increases, within the historical control range, were associated with metabolic overload and acute systemic toxicity. Benchmark dose analysis confirmed a non-linear dose response. The weight of evidence indicates 2,6-xylidine is a non-direct acting (metabolic threshold-dependent) genotoxin, and is not genotoxic in vivo in rats in the absence of acute systemic toxic effects, which occur at levels 35 × beyond lidocaine-related exposure in humans.

Canine orosomucoid (alpha-1 acid glycoprotein) variants and their influence on drug plasma protein binding.

Orosomucoid polymorphisms influence plasma drug binding in humans; however, canine variants and their effect on drug plasma protein binding have not yet been reported. In this study, the orosomucoid gene (ORM1) was sequenced in 100 dogs to identify the most common variant and its allele frequency determined in 1,464 dogs (from 64 breeds and mixed-breed dogs). Plasma protein binding extent of amitriptyline, indinavir, verapamil, and lidocaine were evaluated by equilibrium dialysis using plasma from ORM1 genotyped dogs (n = 12). Free and total drug plasma concentrations were quantified by liquid chromatography-mass spectrometry. From the five polymorphisms identified in canine ORM1, two were nonsynonymous. The most common was c.70G>A (p.Ala24Thr) with an allele frequency of 11.2% (n = 1464). Variant allele frequencies varied by breed, reaching 74% in Shetland Sheepdogs (n = 21). Free drug fractions did not differ significantly (p > .05; Mann-Whitney U) between plasma collected from dogs with c.70AA (n = 4) and those with c.70GG (n = 8) genotypes. While c.70G>A did not affect the extent of plasma protein binding in our study, the potential biological and pharmacological implication of this newly discovered ORM1 variant in dogs should be further investigated.

Anestesia espinal parte III. Mecanismos de acción / Spinal anesthesia part III. Mechanisms of action

Spinal anesthesia is a widely used technique in medical practice nowadays. Generally, nervous blockage is determined by three main factors. The first of them is the distribution of the local anesthetic in the cerebrospinal fluid (CSF), which can be affected by numerous factors, the most important of them being CSF volume. The second is absorption, which is greatest at the sites with higher drug concentration: this is the result of the accessibility, lipidic content and vascular irrigation of each area. The last of these factors is elimination, mediated mainly by the irrigation of the different compartments, and whose order differs from the mirror image of the onset's action order. The previously mentioned elements are the main sources of variation for the time needed to achieve desired effects, order in which fibers are affected and differential blockage. This text describes the principal mechanisms through which spinal anesthesia works, and the factors which can result in variations of its results.

La anestesia espinal es una técnica ampliamente utilizada en la práctica clínica. Por lo general, el bloqueo nervioso está determinado por tres factores principales. El primero es la distribución del anestésico local en el líquido cefalorraquídeo (LCR), que a su vez se ve afectado por una gran variedad de factores, destacando entre estos el volumen de LCR. El segundo es la absorción, la cual es mayor en los sitios en donde la concentración del fármaco también lo es: para esto afecta la accesibilidad, el contenido lipídico y la irrigación vascular de cada zona. El último factor es la eliminación, mediada principalmente por la irrigación de los distintos compartimentos, y cuyo orden es distinto a la imagen especular del inicio de acción. Los factores mencionados son los principales determinantes de los tiempos de demora de los bloqueos, el orden en el que se logra su acción en las distintas fibras y el bloqueo diferencial. Este texto pretende describir los principales mecanismos de acción mediante los cuales actúa la anestesia espinal y los factores que pueden determinar diferencias en los resultados de esta.