High-Dose Bupivacaine Remotely Loaded into Multivesicular Liposomes Demonstrates Slow Drug Release Without Systemic Toxic Plasma Concentrations After Subcutaneous Administration in Humans

Multi-vesicular Liposome and its Applications: A Novel Chemically Modified Approach for Drug Delivery Application

BACKGROUND

This study aimed to elaborate on all the aspects of multivesicular liposomes, including structure, function, topology, etc. Liposomes are a unique drug delivery system, in which both hydrophilic and hydrophobic drug molecules can be incorporated. Particularly, multivesicular liposomes have more advantages than other liposomes because of their unique structure. This study provides an overview of several works already performed by various researchers in this field. Numerous studies have reported on preparing and evaluating multivesicular liposomes for drug delivery applications. This study summarizes the process of formulating multivesicular liposomes and their application in drug delivery systems and provides details about how to resolve the problem of limited solubility and stability of biomolecules, along with controlled drug release kinetics, with the possibility of loading various drugs. There is no doubt that multivesicular liposome opens new avenues to develop novel drug delivery system for achieving the desired functional performances and expanding the applications in the drug delivery area.

Lipid-Based Nanotechnology: Liposome

Over the past several decades, liposomes have been extensively developed and used for various clinical applications such as in pharmaceutical, cosmetic, and dietetic fields, due to its versatility, biocompatibility, and biodegradability, as well as the ability to enhance the therapeutic index of free drugs. However, some challenges remain unsolved, including liposome premature leakage, manufacturing irreproducibility, and limited translation success. This article reviews various aspects of liposomes, including its advantages, major compositions, and common preparation techniques, and discusses present U.S. FDA-approved, clinical, and preclinical liposomal nanotherapeutics for treating and preventing a variety of human diseases. In addition, we summarize the significance of and challenges in liposome-enabled nanotherapeutic development and hope it provides the fundamental knowledge and concepts about liposomes and their applications and contributions in contemporary pharmaceutical advancement.

Application of Advanced Technologies-Nanotechnology, Genomics Technology, and 3D Printing Technology-In Precision Anesthesia: A Comprehensive Narrative Review

There has been increasing interest and rapid developments in precision medicine, which is a new medical concept and model based on individualized medicine with the joint application of genomics, bioinformatics engineering, and big data science. By applying numerous emerging medical frontier technologies, precision medicine could allow individualized and precise treatment for specific diseases and patients. This article reviews the application and progress of advanced technologies in the anesthesiology field, in which nanotechnology and genomics can provide more personalized anesthesia protocols, while 3D printing can yield more patient-friendly anesthesia supplies and technical training materials to improve the accuracy and efficiency of decision-making in anesthesiology. The objective of this manuscript is to analyze the recent scientific evidence on the application of nanotechnology in anesthesiology. It specifically focuses on nanomedicine, precision medicine, and clinical anesthesia. In addition, it also includes genomics and 3D printing. By studying the current research and advancements in these advanced technologies, this review aims to provide a deeper understanding of the potential impact of these advanced technologies on improving anesthesia techniques, personalized pain management, and advancing precision medicine in the field of anesthesia.

Recent advances in lipid-based long-acting injectable depot formulations

Long-acting injectable (LAIs) delivery systems sustain the drug therapeutic action in the body, resulting in reduced dosage regimen, toxicity, and improved patient compliance. Lipid-based depots are biocompatible, provide extended drug release, and improve drug stability, making them suitable for systemic and localized treatment of various chronic ailments, including psychosis, diabetes, hormonal disorders, arthritis, ocular diseases, and cancer. These depots include oil solutions, suspensions, oleogels, liquid crystalline systems, liposomes, solid lipid nanoparticles, nanostructured lipid carriers, phospholipid phase separation gel, vesicular phospholipid gel etc. This review summarizes recent advancements in lipid-based LAIs for delivering small and macromolecules, and their potential in managing chronic diseases. It also provides an overview of the lipid depots available in market or clinical phase, as well as patents for lipid-based LAIs. Furthermore, this review critically discusses the current scenario of using in vitro release methods to establish IVIVC and highlights the challenges involved in developing lipid-based LAIs.

Incisional infiltration versus transversus abdominis plane block of liposomal bupivacaine after midline vertical laparotomy for suspected gynecologic malignancy: a pilot study

Background

To evaluate whether incisional infiltration of liposomal bupivacaine would decrease opioid requirement and pain scores after midline vertical laparotomy for suspected or known gynecologic malignancy compared with transversus abdominis plane (TAP) block with liposomal bupivacaine.

Methods

A prospective, single blind randomized controlled trial compared incisional infiltration of liposomal bupivacaine plus 0.5% bupivacaine versus TAP block with liposomal bupivacaine plus 0.5% bupivacaine. In the incisional infiltration group, patients received 266 mg free base liposomal bupivacaine with 150 mg bupivacaine hydrochloride. In the TAP block group, 266 mg free base bupivacaine with 150 mg bupivacaine hydrochloride was administered bilaterally. The primary outcome was total opioid use during the first 48-hour postoperative period. Secondary outcomes included pain scores at rest and with exertion at 2, 6, 12, 24 and 48 h after surgery.

Results

Forty three patients were evaluated. After interim analysis, a three-fold higher sample size than originally calculated was required to detect a statistically significant difference. There was no clinical difference between the two arms in mean opioid requirement (morphine milligram equivalents) for the first 48 h after surgery (59.9 vs. 80.8, p = 0.13). There were no differences in pain scores at rest or with exertion between the two groups at pre-specified time intervals.

Conclusion

In this pilot study, incisional infiltration of liposomal bupivacaine and TAP block with liposomal bupivacaine demonstrated clinically similar opioid requirement after gynecologic laparotomy for suspected or known gynecologic cancer. Given the underpowered study, these findings cannot support the superiority of either modality after open gynecologic surgery.

DoE development of ionic gradient liposomes: A successful approach to improve encapsulation, prolong anesthesia and decrease the toxicity of etidocaine

Etidocaine (EDC) is a long-acting local anesthetic of the aminoamide family whose use was discontinued in 2008 for alleged toxicity issues. Ionic gradient liposomes (IGL) are nanostructured carriers for which an inner/outer gradient of ions increases drug upload. This work describes IGL_EDC, a formulation optimized by Design of Experiments, composed of hydrogenated soy phosphatidylcholine:cholesterol:EDC, and characterized by DLS, NTA, TEM/Cryo-TEM, DSC and ¹H NMR. The optimized IGL showed significant encapsulation efficiency (41 %), good shelf stability (180 days) and evidence of EDC interaction with the lipid bilayer (as seen by DSC and ¹H NMR results) that confirms its membrane permeation. In vitro (release kinetics and cytotoxicity) tests showed that the encapsulation of EDC into the IGL promoted sustained release for 24 h and decreased by 50 % the intrinsic toxicity of EDC to Schwann cells. In vivo IGL_EDC decreased the toxicity of EDC to Caenorhabditis elegans by 25 % and extended its anesthetic effect by one hour, after infiltrative administration, at clinically used (0.5 %) concentration, in rats. Thus, this novel drug delivery system is a promise for the possible reintroduction of EDC in clinics, aiming at the control of operative and postoperative pain.

Development and in vivo validation of phospholipid-based depots for the sustained release of bupivacaine

By direct deposition of the drug at the local site of action, injectable depot formulations - intended for treatment of a local disease or for local intervention - are designed to limit the immediate exposure of the active principle at a systemic level and to reduce the frequency of administration. To overcome known drawbacks in the production of some marketed phospholipid-based depots, here we propose to manufacture drug-loaded negatively charged liposomes through conventional technologies and to control their aggregation mixing a solution of divalent cations prior to administration. We identified phosphatidylglycerol (PG) as the most suitable phospholipid for controlled aggregation of the liposomes and to modulate the release of the anesthetic bupivacaine (BUP) from liposomal depots. In vivo imaging of the fluorescently-labelled liposomes showed a significantly higher retention of the PG liposomes at the injection site with respect to zwitterionic ones. In situ mixing of PG liposomes with calcium salts significantly extended the area under the curve of BUP in plasma compared to the non-depot system. Overall, controlling the aggregation of negatively charged liposomes with divalent cations not only modulated the particle clearance from the injection site but also the release in vivo of a small amphipathic drug such as BUP.

[Liposomal bupivacaine-No breakthrough in postoperative pain management]

One of the main limitations concerning the use of local anesthetics is due to their restricted duration of action. In recent years, liposomal formulations with prolonged release kinetics have been developed to extend the pharmacological duration of action of the 1‑stage peripheral regional anesthesia (single-shot procedure) and thus bring about a longer duration of action. The focus here is particularly on achieving postoperative freedom from pain for at least 24 h (or even better 48 h) and thus early mobilization of patients using on-demand medication causing (at most) minor local sensory blockade without causing motor impairments (at least that is the ideal). Therefore, methods of utilizing slow-release drugs as seen in liposomal carrier systems have experienced increasing scientific attention in the last few years. A common modern pharmacological example with a theoretically significantly longer duration of action is liposomal bupivacaine, an amide local anesthetic. Due to a multivesicular liposome structure, the retarded release of the active component bupivacaine HCl leads to a theoretical pharmacological effectiveness of up to 72 h. Previous studies consistently showed a safety profile comparable to conventional bupivacaine HCl. Liposomal bupivacaine has been approved by the U.S. Food and Drug Administration (FDA) under the trade name Exparel© (Pacira Pharmaceuticals, Parsippany, NJ, USA) since 2011; however, its use is currently limited to local wound infiltration, transverse abdominis plane (TAP) blocks, and interscalene nerve blocks of the brachial plexus. In 2020, the European Medicines Agency (EMA) also approved the use of liposomal bupivacaine for blockade of the brachial plexus or the femoral nerve and as a field block or for wound infiltration to treat postoperative pain. So far, studies on the clinical effectiveness of liposomal bupivacaine have been very heterogeneous and there have been no conclusive meta-analyses with sufficient rigor or significance. Recent systematic reviews and meta-analyses, combining the results of clinical studies regarding the analgesic efficiency of liposomal bupivacaine in different fields of application, consistently refuted any benefit of clinical relevance provided by the liposomal formulation. There is currently sufficient evidence to now end the ongoing debate around liposomal bupivacaine. The aim of this work is to give the reader a current, evidence-based overview of this substance.

Does the use of periarticular anesthetic cocktail provide adequate pain control following shoulder arthroplasty?

BACKGROUND

Interscalene nerve block and liposomal bupivacaine have been found to provide adequate pain control following shoulder arthroplasty. We hypothesized that local infiltration of a periarticular cocktail would provide equivalent pain control compared to interscalene nerve block and liposomal bupivacaine.

METHODS

Eighty-seven patients undergoing primary shoulder arthroplasty were treated with local infiltration of a periarticular cocktail (200 mg of 0.5% ropivacaine, 1 mg epinephrine, and 30 mg ketorolac), local infiltration of liposomal bupivacaine, or preoperative interscalene nerve block. The outcomes of the study were postoperative visual analog scale scores, opioid consumption, length of stay, and complications.

RESULTS

A total of 30 patients receiving local infiltration of a periarticular cocktail, 26 receiving liposomal bupivacaine, and 31 receiving interscalene nerve block were included in the study. Patients who received local infiltration of a periarticular cocktail had a significantly lower mean visual analog scale when compared to interscalene nerve block and liposomal bupivacaine on postoperative day 0 (2.5 versus 4.0 versus 4.8, P = 0.001 and P < 0.001). Pain scores between postoperative day 0-3 were lower in patients who received local infiltration of a periarticular cocktail, but not significantly. Patients who received local infiltration of a periarticular cocktail required significantly less opioids than the interscalene nerve block group on postoperative day 0 (P < 0.001).

DISCUSSION

A decrease in early postoperative pain and opioid consumption was found with local infiltration of a periarticular cocktail when compared with interscalene nerve block and liposomal bupivacaine after shoulder arthroplasty.Level of evidence: Level II.

Degradable polymeric vehicles for postoperative pain management

Effective control of pain management has the potential to significantly decrease the need for prescription opioids following a surgical procedure. While extended release products for pain management are available commercially, the implementation of a device that safely and reliably provides extended analgesia and is sufficiently flexible to facilitate a diverse array of release profiles would serve to advance patient comfort, quality of care and compliance following surgical procedures. Herein, we review current polymeric systems that could be utilized in new, controlled post-operative pain management devices and highlight where opportunities for improvement exist.

Clinical Effectiveness of Liposomal Bupivacaine Administered by Infiltration or Peripheral Nerve Block to Treat Postoperative Pain

The authors provide a comprehensive summary of all randomized, controlled trials (n = 76) involving the clinical administration of liposomal bupivacaine (Exparel; Pacira Pharmaceuticals, USA) to control postoperative pain that are currently published. When infiltrated surgically and compared with unencapsulated bupivacaine or ropivacaine, only 11% of trials (4 of 36) reported a clinically relevant and statistically significant improvement in the primary outcome favoring liposomal bupivacaine. Ninety-two percent of trials (11 of 12) suggested a peripheral nerve block with unencapsulated bupivacaine provides superior analgesia to infiltrated liposomal bupivacaine. Results were mixed for the 16 trials comparing liposomal and unencapsulated bupivacaine, both within peripheral nerve blocks. Overall, of the trials deemed at high risk for bias, 84% (16 of 19) reported statistically significant differences for their primary outcome measure(s) compared with only 14% (4 of 28) of those with a low risk of bias. The preponderance of evidence fails to support the routine use of liposomal bupivacaine over standard local anesthetics.

Liposomal Bupivacaine (Bupigel) Demonstrates Minimal Local Nerve Toxicity in a Rabbit Functional Model

We previously reported the development of a novel formulation of an ultra-long-acting local anesthetic based on bupivacaine encapsulated in large multivesicular liposomes (Bupisomes) embedded in hydrogel. This formulation (Bupigel) prolonged bupivacaine release from the formulation in dissolution-like studies in vitro and analgesia in vivo in mouse, rat, and pig models. In this study we assessed Bupigel neurotoxicity on rabbit sciatic nerve using histopathology and electrophysiologic testing. Sciatic nerves of both hind limbs were injected dropwise with different formulations. Nerve conduction studies and needle electromyography two weeks after perineural administration showed signs of neural damage after injection of free lidocaine and bupivacaine, while there was no sign of neural damage after injection with saline, demonstrating the validity of the method. This test also did not show evidence of motor or sensory nerve damage after injection with liposomal bupivacaine at a dose 10-times higher than free bupivacaine. Histologically, signs of neural damage could be observed with lidocaine. Nerves injected with Bupigel showed mild signs of inflammation and small residues of hydrogel in granulomas, indicating a long residence time of the hydrogel at the site of injection, but no histopathological signs of nerve damage. This demonstrated that early signs of neural damage were detected electrophysiologically, showing the usefulness and sensitivity of electrodiagnostic testing in detection of neural damage from new formulations.

A prospective randomized trial comparing liposomal bupivacaine vs standard bupivacaine wound infiltration in open gynecologic surgery on an enhanced recovery pathway

BACKGROUND

Value in healthcare is reflected by patient-centered outcomes of care per health dollar expended. Although liposomal bupivacaine is more expensive, it has been shown to provide prolonged analgesia (up to 72 hours).

OBJECTIVE

This study aimed to evaluate whether the addition of liposomal bupivacaine to standard bupivacaine could decrease opioid intake and improve pain control after laparotomy for gynecologic surgery compared with standard bupivacaine alone in an enhanced recovery after surgery pathway.

STUDY DESIGN

A prospective randomized controlled single-blinded trial of wound infiltration with liposomal bupivacaine plus 0.25% bupivacaine (study arm) vs 0.25% bupivacaine (control arm) was performed at a National Cancer Institute-designated tertiary referral cancer center. Participants were patients aged ≥18 years undergoing exploratory laparotomy for a gynecologic indication. All patients were treated on an enhanced recovery pathway including local wound infiltration before closure. In this study, 266 mg of liposomal bupivacaine (free base; equal to 300 mg bupivacaine HCL)+150 mg of bupivacaine mixed in the same syringe was used in the study arm, and 150 mg of bupivacaine was used in the control arm. The primary outcome was the proportion of patients who were opioid-free within 48 hours after surgery. Secondary outcomes included number of opioid-free days from postoperative day 0 to postoperative day 3, days to first opioid administration, morphine equivalent daily dose, and patient-reported outcomes collected with the MD Anderson Symptom Inventory. The MD Anderson Symptom Inventory was administered as a preoperative baseline, daily while hospitalized, and at least weekly for 8 weeks after discharge. All outcomes were prespecified before data collection.

RESULTS

In this study, 102 patients were evaluated. Among them, 16.7% of patients in the study arm received no opioids up to 48 hours compared with 14.8% in the control arm (P=.99). There were no significant differences in the amount of intraoperative opioids administered or days to first opioid use. There was no significant difference between the 2 arms in median cumulative morphine equivalent daily dose (21.3 [study arm] vs 33.8 [control arm]; P=.36) or between the groups in morphine equivalent daily dose per individual day. There were no significant differences in patient-reported pain or interference with walking between the 2 arms or other patient-reported outcomes.

CONCLUSION

Within an enhanced recovery after surgery pathway, adding liposomal bupivacaine to 0.25% bupivacaine wound infiltration did not decrease the proportion of patients who were opioid-free within 48 hours after surgery, did not decrease opioid intake, or did not improve patient's self-reported pain and functional recovery compared with standard bupivacaine.

Enhanced Recovery With Paravertebral and Transversus Abdominis Plane Blocks in Microvascular Breast Reconstruction

Purpose:

We have shown previously that a preoperative paravertebral nerve block is associated with improved postoperative recovery in microvascular breast reconstruction. The purpose of this study was to compare the outcomes of a complete enhanced recovery after surgery (ERAS) protocol with complete regional anesthesia coverage to our traditional care with paravertebral block.

Patients and methods:

This was a retrospective cohort study of 83 patients who underwent autologous breast reconstruction by T.M.M. between May 2014 and February 2018 at a tertiary academic center. Patients in the ERAS group were additionally administered acetaminophen, non-steroidal anti-inflammatory drugs (NSAIDs), gabapentin, a transversus abdominis plane block (liposomal or plain bupivacaine), and primarily oral opioids postoperatively. The patients were mobilized earlier with more rapid diet progression. All patients received a preoperative paravertebral block.

Results:

Forty-four patients in the ERAS cohort were compared with 39 retrospective controls. The 2 groups were similar with respect to demographics and comorbidities. The ERAS cohort required significantly less opioids (291 vs 707 mg oral morphine equivalent, P < .0001) with unchanged postoperative pain scores and a shorter time to oral only opioid use (16.0 vs 78.2 hours, P < .0001). Median length of stay (3.20 vs 4.62, P < .0001) and time to independent ambulation (1.86 vs 2.88, P < .0001) were also significantly decreased in the ERAS cohort. Liposomal bupivacaine use did not significantly affect the results (P ⩾ .2).

Conclusions:

Implementation of a robust enhanced recovery protocol with complete regional anesthesia coverage was associated with significantly decreased opioid use despite unchanged pain scores, with improved markers of recovery including length of stay, time to oral only narcotics, and time to independent ambulation.

Perineural dexamethasone attenuates liposomal bupivacaine-induced delayed neural inflammation in mice in vivo

BACKGROUND

Liposomal bupivacaine (Exparel®) is a sustained-release formulation of bupivacaine for use in surgical infiltration anaesthesia. We analysed the histological nerve toxicity and clinical effectiveness of perineural Exparel® alone or with added dexamethasone in a mouse model.

METHODS

We assigned 98 mice receiving a perineural sciatic nerve injection into seven groups: sham (n=14, perineural saline), B (n=14, perineural bupivacaine), BDIP (n=14, perineural bupivacaine + intraperitoneal dexamethasone), BDPN (n=14, perineural bupivacaine + perineural dexamethasone), E (n=14, perineural Exparel®), EDIP (n=14, perineural Exparel® + intraperitoneal dexamethasone), and EDPN (n=14, perineural Exparel® + perineural dexamethasone). The duration of thermoalgesic and motor block was evaluated in 49 mice (seven mice randomly selected by group) every 30 min until recovery. Mice were killed for sciatic nerve histological assessment at 14 or 28 days.

RESULTS

The median duration of motor block was 90, 120, 120, 120, 180, and 180 min and the duration of thermoalgesic block was 240, 300, 360, 360, 360, and 420 min for groups B, BDIP, BDPN, E, EDIP, and EDPN, respectively. The B group mice showed mild neural inflammation at 14 days and the E group mice showed mild neural inflammation at 28 days. Addition (intraperitoneal or perineural) of dexamethasone reduced neural inflammation induced by bupivacaine, whereas only perineural dexamethasone reduced neural inflammation induced by Exparel®.

CONCLUSIONS

Perineural or systemic dexamethasone had a protective effect against the neural inflammation induced by bupivacaine, and perineural dexamethasone attenuated delayed inflammation induced by perineural Exparel®.

Pharmacokinetics and Pharmacodynamics Modeling and Simulation Systems to Support the Development and Regulation of Liposomal Drugs

Liposomal formulations have been developed to improve the therapeutic index of encapsulated drugs by altering the balance of on- and off-targeted distribution. The improved therapeutic efficacy of liposomal drugs is primarily attributed to enhanced distribution at the sites of action. The targeted distribution of liposomal drugs depends not only on the physicochemical properties of the liposomes, but also on multiple components of the biological system. Pharmacokinetic⁻pharmacodynamic (PK⁻PD) modeling has recently emerged as a useful tool with which to assess the impact of formulation- and system-specific factors on the targeted disposition and therapeutic efficacy of liposomal drugs. The use of PK⁻PD modeling to facilitate the development and regulatory reviews of generic versions of liposomal drugs recently drew the attention of the U.S. Food and Drug Administration. The present review summarizes the physiological factors that affect the targeted delivery of liposomal drugs, challenges that influence the development and regulation of liposomal drugs, and the application of PK⁻PD modeling and simulation systems to address these challenges.

A Randomized Controlled Trial of Liposomal Bupivacaine Parasternal Intercostal Block for Sternotomy

BACKGROUND

Optimal pain control continues to be a concern in cardiac surgery. Current strategies for postoperative pain management often yield suboptimal results. The superiority of Exparel (Pacira Pharmaceuticals, Inc, Parsippany, NJ) in providing postoperative pain control and opioid sparing is equivocal. This prospective, randomized, double-blind study examines the efficacy of Exparel as a novel single-dose application parasternal nerve block in postoperative pain control and opioid sparing.

METHODS

This single-surgeon study included 79 patients undergoing median sternotomy for coronary revascularization. Study participants were randomized to either the drug or a control arm. Each participant received Exparel or normal saline placebo administered as a parasternal nerve block. Postoperative pain was rated according to the nonverbal pain scale or numeric rating scale. Total amount of narcotic pain medication used and patients' pain scores within the first 72 hours postoperatively were compared. Secondary outcomes compared the intensive care unit length of stay, hospital length of stay, time to extubation, time to return of bowel function, and time to return to work or daily activities.

RESULTS

The primary endpoint of pain levels between the two groups demonstrated no significant difference when analyzing the individual time points postoperatively. However, overall pain levels were significantly lower in the study drug group (p = 0.04). There was no significant difference in the amount of analgesics required postoperatively or in secondary endpoints between the groups.

CONCLUSIONS

Exparel does not provide an opioid-sparing benefit or any secondary outcome benefit compared with placebo. Exparel may be associated with a marginal decrease in postoperative pain levels. (Parasternal Nerve Bock in Cardiac Patients; NCT01826851.).

Thumb Basal Joint Arthroplasty: Prospective Comparison of Perioperative Analgesia and Opioid Consumption

Trapeziectomy alone or in combination with a suspensionplasty technique is a common surgical treatment for symptomatic thumb basal joint arthritis. The authors undertook a prospective comparative study to test the hypothesis that peripheral nerve blocks would provide better pain control than local anesthesia with bupivacaine or liposomal bupivacaine regarding pain scores and opioid pill consumption. Patients who elected to undergo basal joint arthroplasty were allocated to 1 of 3 postoperative pain management groups: (1) peripheral nerve block, (2) local anesthesia with bupivacaine, or (3) local anesthesia with liposomal bupivacaine. Total opioid pill consumption and visual analog scale pain scores were reported for the first 5 postoperative days (PODs). Seventy-eight patients were enrolled, with 27, 23, and 28 patients in the peripheral nerve block, bupivacaine, and liposomal bupivacaine groups, respectively. All groups experienced an increase in opioid pill consumption and visual analog scale pain scores from POD 0 to POD 1. Postoperative visual analog scale pain scores were lowest in group 3 from POD 0 to POD 2. Average visual analog scale pain scores were highest in group 1, except for on POD 0. After POD 2, visual analog scale pain scores normalized between all groups and decreased uniformly thereafter. Total opioid consumption was lowest in group 3 (average, 11 pills) compared with group 1 (average, 17 pills) and group 2 (average, 19 pills). Overall, these findings did not support the authors' hypothesis that peripheral nerve blocks are superior in terms of postoperative pain control and opioid consumption. Although there were advantages regarding opioid consumption and pain control with liposomal bupivacaine, these were limited to the first POD. The effectiveness of each modality, as well as potential risks and costs, should be considered when determining the optimal strategy. [Orthopedics. 2018; 41(3):e410-e415.].

Bupivacaine in alginate and chitosan nanoparticles: an in vivo evaluation of efficacy, pharmacokinetics, and local toxicity

Objective

This study reports a preclinical evaluation of an alginate/chitosan nanoparticle formulation containing NovaBupi®, a racemic bupivacaine (BVC) containing 25% dextrobupivacaine and 75% levobupivacaine.

Methods

New Zealand White rabbits (n=6) received intraoral or intrathecal injections of BVC 0.5% or BVC 0.5%-loaded alginate–chitosan nanoparticles (BVC_ALG). BVC plasma levels and pharmacokinetic parameters were determined in blood samples of these rabbits. An infraorbital nerve blockade was performed in male Wistar rats (n=7) with the same formulations and the vehicle (NP_ALG). Histological evaluation of local toxicity after 6 hours and 24 hours of the treatments was performed in rats’ (n=6) oral tissues.

Results

No statistically significant difference was observed between plasma concentrations and pharmacokinetic parameters (p>0.05) after intraoral injections. However, after intrathecal injection BVC_ALG changed approximately three times the values of volume of distribution and area under the curve (AUC_0–t; p<0.05). The total analgesic effect of BVC after infraorbital nerve blockade was improved by 1.4-fold (p<0.001) with BVC_ALG. BVC and BVC_ALG did not induce significant local inflammatory reaction.

Conclusion

The encapsulation of BVC prolongs the local anesthetic effect after infraorbital nerve blockade and altered the pharmacokinetics after intrathecal injection.

Development of bupivacaine decorated reduced graphene oxide and its local anesthetic effect-In vivo study

The present works aims to develop bupivacaine modified reduced graphene oxide (BPV/RGO), and comparative evaluation of their anesthetic effect with free bupivacaine (BPV). The prepared BPV/RGO was studied by using various spectroscopic and microscopic characterization studies. In vitro drug release from BPV/RGO was studied using HPLC analysis. The cytotoxicity of BPV/RGO was studied against fibroblast (3T3) cells. In vivo evaluation of anesthetic effects was performed on animal models. BPV/RGO showed a prolonged in vitro release and lower cytotoxicity when compared to free BPV. Also, BPV/RGO showed a significantly prolonged analgesic effect when compared to free BPV. Further, the prepared BPV/RGO drug delivery system demonstrated to function as gifted to overcome the drawbacks of free BPV and other available drug delivery systems by prolonging the anesthetic effect with poor cytotoxicity.

Systemic Safety of Liposomal Bupivacaine in Simultaneous Bilateral Total Knee Arthroplasty

BACKGROUND

Intraoperative periarticular injections (PAIs) with local anesthetic are an important component of multimodal pain control in total joint arthroplasty. Liposomal bupivacaine is an extended-release formulation of bupivacaine designed to provide extended pain relief, approved for use in a single surgical site. The systemic safety profile for use in simultaneous bilateral TKA (bTKA) with a full dose in each knee has not been evaluated. The purpose of this study was to determine the safety and pharmacokinetics of bilateral full-dose PAI liposomal bupivacaine in the blood collected in patients undergoing simultaneous bTKA.

METHODS

In this prospective study, patients had an identical PAI consisting of 20 cc of liposomal bupivacaine (266 mg), 30 cc of 0.25% bupivacaine (75 mg) with epinephrine, and 10 cc of normal saline injected into each knee during bTKA. Blood samples were collected at predefined intervals until patient discharge. No exogenous bupivacaine was administered. Pharmacokinetic evaluations were subsequently performed and compared to bupivacaine toxicity levels. Patients were monitored for adverse events related to anesthetic toxicity (cardiac and neurologic).

RESULTS

Fifteen patients (mean age, 60.7 years; range, 57-64 years) were enrolled in the study. The mean peak level (Cmax) was 0.8 μg/mL (range, 0.4-1.2 μg/mL). All patients were well below the reported systemic cardiac and toxicity levels reported as 2-4 μg/mL. There were no reported cardiac and neurotoxic events in any patients.

CONCLUSION

The use of full-dose PAI with liposomal bupivacaine placed into each knee during simultaneous bTKA is safe with systemic bupivacaine levels well below reported cardiac and neurotoxic levels.

Liposomal Formulations in Clinical Use: An Updated Review

Liposomes are the first nano drug delivery systems that have been successfully translated into real-time clinical applications. These closed bilayer phospholipid vesicles have witnessed many technical advances in recent years since their first development in 1965. Delivery of therapeutics by liposomes alters their biodistribution profile, which further enhances the therapeutic index of various drugs. Extensive research is being carried out using these nano drug delivery systems in diverse areas including the delivery of anti-cancer, anti-fungal, anti-inflammatory drugs and therapeutic genes. The significant contribution of liposomes as drug delivery systems in the healthcare sector is known by many clinical products, e.g., Doxil®, Ambisome®, DepoDur™, etc. This review provides a detailed update on liposomal technologies e.g., DepoFoam™ Technology, Stealth technology, etc., the formulation aspects of clinically used products and ongoing clinical trials on liposomes.

Local anesthetic effects of bupivacaine loaded lipid-polymer hybrid nanoparticles: In vitro and in vivo evaluation

PURPOSE

There is a compelling need for prolonged local anesthetic that would be used for analgesia with a single administration. However, due to the low molecular weight of local anesthetics (LA) (lidocaine, bupivacaine, procaine, dibucaine, etc), they present fast systemic absorption.

METHODS

The aim of the present study was to develop and evaluate bupivacaine lipid-polymer hybrid nanoparticles (BVC LPNs), and compared with BVC loaded PLGA nanoparticles (BVC NPs). Their morphology, particle size, zeta potential and drug loading capacity were evaluated. In vitro release study, stability and cytotoxicity were studied. In vivo evaluation of anesthetic effects was performed on animal models.

RESULTS

A facile nanoprecipitation and self-assembly method was optimized to obtain BVC LPNs, composed of PLGA, lecithin and DSPE-PEG₂₀₀₀, of ∼175nm particle size. Compared to BVC NPs, BVC LPNs exhibited prolonged in vitro release in phosphate-buffered saline (pH=7.4). Further, BVC LPNs displayed enhanced in vitro stability in 10% FBS and lower cytotoxicity (the concentration of BVC ranging from 1.0μM to 20μM). In addition, BVC LPNs exhibited significantly prolonged analgesic duration.

CONCLUSION

These results demonstrate that the LPNs could function as promising drug delivery system for overcoming the drawbacks of poor stability and rapid drug leakage, and prolonging the anesthetic effect with slight toxicity.

No Difference in Early Analgesia Between Liposomal Bupivacaine Injection and Intrathecal Morphine After TKA

BACKGROUND

Opioid analgesics have been a standard modality for postoperative pain management after total knee arthroplasty (TKA) but are also associated with increased risk of nausea, pruritus, vomiting, respiratory depression, prolonged ileus, and cognitive dysfunction. There is still a need for a method of anesthesia that can deliver effective long-term postoperative pain relief without incurring the high cost and health burden of opioids and nerve blocks.

QUESTIONS/PURPOSES

(1) Is liposomal bupivacaine-based periarticular injection (PAI) more effective than morphine-based spinal anesthesia or ropivacaine-based PAI in controlling postoperative pain after TKA? (2) Do patients treated with liposomal bupivacaine-based PAI experience fewer opioid-related adverse events compared with patients treated with morphine-based spinal anesthesia or ropivacaine-based PAI in controlling postoperative pain after TKA?

METHODS

This multicenter, blind trial randomized 119 patients undergoing TKA with spinal anesthesia to receive spinal anesthesia plus periarticular injection with liposomal bupivacaine (40 patients), spinal anesthesia with bupivacaine plus intrathecal morphine (41 patients) but no liposomal bupivacaine injection, or spinal anesthesia with bupivacaine (38 patients) and no liposomal bupivacaine injection. The two groups that did not receive periarticular liposomal bupivacaine did receive periarticular injection with ropivacaine, and all three groups had ketorolac (30 mg) plus epinephrine (1:1000) in the periarticular injections. Patients in all three groups received identical perioperative multimodal analgesic and antiemetic drugs. All patients were analyzed in the group to which they were randomized and no patients were lost to followup. The primary study endpoints were visual analog score (VAS) for pain and narcotic use during postoperative day 1. Secondary endpoints included side effects associated with narcotic administration during the hospital stay.

RESULTS

Mean VAS pain in the liposomal bupivacaine PAI group was lower than that for the ropivacaine PAI group at 6 hours (1.8 ± 2.1 versus 3.3 ± 2.3, p = 0.005, mean difference: 1.5, 95% confidence interval [CI], 0.5-2.5) and 12 hours (1.5 ± 2.0 versus 3.3 ± 2.4, p < 0.001, mean difference: 1.8, 95% CI, 0.8-2.8) after surgery. The morphine spinal group had lower pain compared with the liposomal bupivacaine PAI group at 6 hours (0.9 ± 1.8 versus 1.8 ± 2.1, p = 0.035, mean difference: 1.0, 95% CI, 0.1-1.8), but there was no difference at 12 hours (0.8 ± 1.5 versus 1.5 ± 2.0, p = 0.086, mean difference: 0.7, 95% CI, -0.1 to 1.5). The magnitude of the differences at 6 and 12 hours are near the lower end of minimal clinically important differences reported in the literature, and thus the improvement shown in this study may only represent a small clinical improvement. Both the liposomal bupivacaine group (13% [five of 40]) and the ropivacaine group (5% [two of 38]) had fewer incidents of itching (pruritus) than the spinal morphine group (38% [15 of 41]) (p = 0.001).

CONCLUSIONS

This prospective multicenter three-arm blind randomized controlled trial showed potentially improved pain control at 6 and 12 hours in the liposomal bupivacaine and intrathecal morphine groups compared with the ropivacaine group at the cost of much higher incidences of pruritus (itching) in the intrathecal morphine group. Based on these results, we prefer the use of PAI with liposomal bupivacaine as an alternative to spinal anesthesia with intrathecal morphine as a result of similar postoperative pain control and the potential for reducing adverse events.

LEVEL OF EVIDENCE

Level I, therapeutic study.

A Novel Proliposomal Ropivacaine Oil: Pharmacokinetic-Pharmacodynamic Studies After Subcutaneous Administration in Pigs

BACKGROUND

Liposomal local anesthetics are limited by a short liposomal shelf-life, even when under refrigeration. We describe a novel proliposomal ropivacaine that produces liposomes in situ, only after exposure to aqueous media.

METHODS

In vitro: Nanoparticles were assessed (particle size distribution analyzer, cryo-transmission electron microscopy) at baseline and after exposure to saline/plasma.

TOXICITY

In porcine wound healing study (n = 12), healing was assessed by photography, clinical assessment, and histology. Pharmacodynamics: Seventeen young piglets were randomly assigned to plain 0.5% ropivacaine (n = 5), proliposomal 4% ropivacaine (n = 6), or sham (n = 6). Tactile threshold was assessed using von Frey filaments applied to the surgical wound; the nonoperated skin was used as a control. Tactile threshold over time was determined using area under the curve (AUC) and assessed by 1-way analysis of variance.

PHARMACOKINETICS

8 young piglets were randomly assigned to plain 0.5% (25 mg, n = 4) or proliposomal 4% (200 mg, n = 4) ropivacaine. Plasma ropivacaine was assessed by high-performance liquid chromatography at baseline and at intervals over 36 hours. Paired ropivacaine concentration (from wound exudate and plasma) was obtained at 96 hours. Data were analyzed using noncompartmental and compartmental models.

RESULTS

In vitro: On exposure to saline and plasma, the study drug was transformed from a homogenous oil to an emulsion containing liposomes of approximately 1.4-μm diameter; this effect was dilution dependent and stable over time.

TOXICITY

All wounds healed well; no effect of drug group was observed. Pharmacodynamics: Plain and proliposomal ropivacaine provided sensory anesthesia for approximately 6 and 30 hours, respectively. There was an approximately 7-fold increase in the AUC of anesthesia for proliposomal ropivacaine compared with plain ropivacaine (mean difference, 1010; 95% confidence interval [CI], 625-1396 g·h/mm; P < 0.0001).

PHARMACOKINETICS

There was no difference in Cmax (2.31 ± 0.74 vs 2.32 ± 0.46 mg/L), despite an approximately 8-fold difference in dose. However, proliposomal ropivacaine was associated with a marked prolongation of Tmax (6.50 ± 6.35 vs 0.5 ± 0.0 hours), terminal half-life (16.07 ± 5.38 vs 3.46 ± 0.88 hours; P = 0.0036), and ropivacaine-time AUC (47.72 ± 7.16 vs 6.36 ± 2.07 h·mg/L; P < 0.0001), when compared with plain ropivacaine. The proliposomal formulation provided an approximately 250-fold higher ropivacaine concentration in the surgical wound (mean difference, 3783 ng/mL; 95% CI, 1708-5858; P = 0.001) and an approximately 25-fold higher wound:plasma ropivacaine concentration ratio (mean difference, 126; 95% CI 38-213; P = 0.011).

CONCLUSIONS

Proliposomal ropivacaine exerted prolonged anesthesia with delayed elimination, typical for liposomal drugs. The advantage of this novel proliposomal ropivacaine is its ease of preparation and its extended shelf-stability (>2 years) at room temperature.

Proliposomal Ropivacaine Oil: Pharmacokinetic and Pharmacodynamic Data After Subcutaneous Administration in Volunteers

BACKGROUND

Slow-release liposomal formulations of local anesthetics prolong plasma redistribution and reduce peak plasma drug concentration, allowing safer administration of larger doses and further prolonging sensory effects. However, their clinical applicability is limited by expensive manufacture and liposomal leakage. Previously, we described the simple preparation of a novel proliposomal ropivacaine oil that produces multilamellar liposomal vesicles on exposure to aqueous media and that has a shelf-life of >2 years at room temperature. In this study, we present both pharmacodynamic and pharmacokinetic data in healthy volunteers after subcutaneous injection of this novel proliposomal preparation of ropivacaine.

METHODS

In the pharmacodynamic phase of this study, 15 volunteers received 3 separate subcutaneous injections of 2.5 mL containing 1 of the following drugs: proliposomal 4% ropivacaine, plain 0.5% ropivacaine, and the ropivacaine-free proliposomal vehicle. Drugs were administered into the lower back, and their location was randomized and blinded; a separate area was used as an uninjected, open control. Experimental sensory assessment was made at repeated intervals over 72 hours using both pinprick sensation and experimental heat pain tolerance (assessed using quantitative sensory testing). In a separate pharmacokinetic phase of this study, 9 volunteers received subcutaneous injections of 2.5 mL of either proliposomal 4% ropivacaine (n = 6) or plain 0.5% ropivacaine (n = 3); these participants had plasma ropivacaine concentrations assessed at repeated intervals over 72 hours.

RESULTS

The mean ± SE duration of pinprick anesthesia after proliposomal and plain ropivacaine administration lasted 28.8 ± 6.0 and 15.9 ± 3.5 hours, respectively (mean difference, 16.8 hours; 95% confidence interval, 10.0-23.7; P = 0.001). For experimental heat pain, the anesthesia duration was approximately 36 and 12 hours, respectively, with mean ± SE area under the curve of the normalized heat pain tolerance over time 55.0 ± 28.8 Δ°C·min for proliposomal ropivacaine and 9.6 ± 26.0 Δ°C·min for plain ropivacaine (mean difference, 64.6 Δ°C·min; 95% confidence interval, 10.2-119.0; P = 0.036). In the pharmacokinetic study, there was no significant difference in peak plasma concentration in the proliposomal ropivacaine group (164 ± 43 ng/mL compared with 100 ± 41 ng/mL in the plain ropivacaine group; P = 0.07) despite an 8-fold increase in ropivacaine dose in the proliposomal group. The 99% upper prediction limit for peak plasma concentrations (351 ng/mL proliposomal; 279 ng/mL plain) was well below the putative toxic plasma concentration for both groups. The mean ± SE terminal half-life and area under the curve for proliposomal ropivacaine versus plain ropivacaine were 13.8 ± 3.6 hours vs 5.9 ± 2.3 hours (P = 0.011) and 5090 ± 1476 h·ng/mL vs 593 ± 168 h·ng/mL (P = 0.0014), respectively.

CONCLUSIONS

The prolonged pharmacodynamic effect of proliposomal ropivacaine, together with its delayed elimination and prolonged redistribution to plasma, is compatible to depot-related slow-release and similar to the performance of other liposomal local anesthetics. The advantage of the proliposomal oil is its ease of preparation and its extended shelf-stability at room temperature.

Liposomal bupivacaine for regional anesthesia

PURPOSE OF REVIEW

Using a regional block in a multimodal approach to postoperative analgesia management involves addressing, which local anesthetic and how much should be used to ensure adequate pain relief to reduce related morbidity and mortality. This article will review literature surrounding the recently approved formulation of slow release liposomal bupivacaine, define its proven benefits, and identify ongoing studies to further examine the utility of this novel formulation by various routes.

RECENT FINDINGS

Recent Phase II and III clinical trials have demonstrated the ability of liposomal bupivacaine to provide prolonged analgesia, maintain a high safety profile in therapeutic doses, and decrease opioid requirements when compared with placebo in local infiltration applications for up to 24 h. Between 24 and 72 h after study drug administration, there was minimal to no difference between EXPAREL and placebo treatments on mean pain intensity. Conventional bupivacaine or ropivacaine groups (current standard practice in many hospitals in the USA) were not compared. In addition, the analgesic efficacy, cost-effectiveness, and safety profile of liposomal bupivacaine has not thoroughly been studied in various standard clinical settings such as perineural, intrathecal, and epidural administration.

SUMMARY

Current published data do not provide superior clinical results for EXPAREL over conventional bupivacaine based upon the lack of adequately powered multicentered clinical trials with comparison groups. Further investigation is necessary to identify the analgesic efficacy and safety profile of liposomal bupivacaine versus standard local anesthetics and to define the optimal clinical indication for liposomal bupivacaine administration in regional anesthesia.

Femoral Nerve Block Versus Long-Acting Wound Infiltration in Total Knee Arthroplasty

Multimodal wound infiltration analgesic techniques have attracted growing interest for applications in total knee arthroplasty (TKA). A benefit of using wound infiltration instead of femoral nerve block (FNB) in a multimodal pain control regimen is the limitation of muscle strength impairment to the surgical area, which will focus the pain control effort and may provide the opportunity for easier rehabilitation and earlier discharge from the hospital. The current study directly compares patients undergoing TKA who are given a continuous FNB with those who were administered an injection of liposomal bupivacaine infiltration. The study cohort included 36 patients with osteoarthritis who were treated with a continuous FNB (OnQ pump; I-Flow, Lake Forest, California), and 36 patients who were administered an injection for liposome bupivacaine infiltration (EXPAREL; Pacira Pharmaceuticals, Inc, Parsippany, New Jersey) for postoperative pain analgesia. The average number of narcotic doses and the total number of narcotics consumed was greater in the FNB group (P<.001). Average visual analog scale pain scores trended higher for patients in the FNB group (2.29 vs 1.93) overall and for each day postoperatively up to day 5, although the overall difference was not significant in this study sample (P=.115). The results of the current study support the conclusion that long-acting liposome bupivacaine infiltration gives comparable postoperative analgesia compared with a continuous FNB, but with significantly less narcotic medication. [Orthopedics. 2016; 39(3):e449-e455.].

Effects of Continuous Peritubal Local Anesthetic Instillation on Postoperative Pain After Percutaneous Nephrolithotomy: A Prospective, Randomized Three-Arm Study

OBJECTIVE

We evaluated the effects of continuous instillation of a local anesthetic at the nephrostomy site on postoperative pain following percutaneous nephrolithotomy (PCNL).

PATIENTS AND METHODS

Sixty patients who underwent PCNL between August 2013 and March 2015 were enrolled in this randomized prospective study. The following three groups comprising 20 patients each were analyzed: Group A, continuous infiltration of local anesthetic at the nephrostomy site; Group B, local anesthetic injected only once; and Group C, 0.9% saline injected as a control at the end of the procedure. Postoperative patients reported pain scores, and amount of analgesic use was recorded at 2, 6, 12, 24, and 48 hours after the surgery.

RESULTS

The mean pain scores of patients in Group A and B were significantly lower compared with Group C patients as much as 12 hours postoperatively (p = 0.001). However, at 24 hours postoperatively, the mean pain scores of Group B and C patients became comparable, while those of Group A patients remained significantly lower until 48 hours after the surgery (p < 0.001). Patients in Group A and C demanded the least and greatest amounts of analgesics, respectively, at all-time intervals (all p < 0.05).

CONCLUSIONS

Continuous infiltration of a local anesthetic is effective for both managing pain immediately after surgery and in dealing with pain that occurs late in the recovery period.

Liposomal Bupivacaine: A Comparative Study of More Than 1000 Total Joint Arthroplasty Cases

Pain after total joint arthroplasty (TJA) can be severe and difficult to control. A single-dose local analgesic delivers bupivacaine in a liposomal time-release platform. In 2248 consecutive patients with hip and knee arthroplasty, half (Pre) were treated using a well-established multimodal analgesia, including periarticular injection (PAI), and half had the PAI substituted for a liposomal bupivacaine injection technique (Post). Pain scores were significantly lower for patients in the Post group for both hip and knee procedures. A large series of patients who had TJA experienced pain relief after the introduction of liposomal bupivacaine as part of an established multimodal protocol.

Liposomal bupivacaine in forefoot surgery

BACKGROUND

Liposomal bupivacaine is increasingly being utilized in attempts to provide prolonged local analgesia in the immediate postoperative period. The purpose of this study was to quantify the reduction in opioid consumption as well as postoperative pain scores in the postoperative period when liposomal bupivacaine is used at the conclusion of forefoot surgery.

METHODS

This was a prospective therapeutic cohort study with 20 patients receiving liposomal bupivacaine at the conclusion of their forefoot procedure in addition to our routine multimodal analgesic protocol and 20 patients as the control without the addition of liposomal bupivacaine. Pain scores, number of narcotic pills consumed on postoperative days 1 through 4, need for refill, time to first refill and wound complications were evaluated.

RESULTS

Mean number of narcotic pills consumed on postoperative day 1 (1.4 vs 3.6, P = .002) and day 2 (1.8 vs 3.6, P = .021) was significantly lower for the liposomal bupivacaine group than the control group. Daily pain scores were lower for those patients who received liposomal bupivacaine on postoperative days 1 through 4, although this was not statistically significant. Fewer patients required medication refills in the liposomal bupivacaine group compared to the control group, however this was not statistically significant (3 vs 7, P = .273). There was no increase in wound complications in the liposomal bupivacaine group when compared to the control (1 vs 4).

CONCLUSION

Liposomal bupivacaine appears to be a useful adjunct in the treatment of postoperative pain when used as a part of a multimodal analgesic regimen in patients undergoing forefoot surgery.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Local pathology and systemic serum bupivacaine after subcutaneous delivery of slow-releasing bupivacaine microspheres

BACKGROUND

Prolonged local anesthesia, particularly desirable to minimize acute and chronic postoperative pain, has been provided by microspheres that slowly release bupivacaine (MS-Bup). In this study, we report on the systemic drug concentrations and the local dermatopathology that occur after subcutaneous injection of MS-Bup.

METHODS

Rats (approximately 300 g) were injected under the dorsolumbar skin with MS-Bup containing 40 mg of bupivacaine (base) or with 0.4 mL of 0.5% bupivacaine-HCl (BupHCl; 1.78 mg bupivacaine). Blood was drawn, under sevoflurane anesthesia, at 10 minutes to 144 hours, and the serum analyzed for total bupivacaine by liquid chromatography-tandem mass spectrometry. In different animals, skin punch biopsies (4 mm) were taken at 1, 3, 7, 14, and 30 days after the same drug injections, sectioned at 5 μm, and stained with hematoxylin-eosin. Samples from skin injected with BupHCl, with MS-Bup suspended in carboxymethyl cellulose (MS-Bup.CMC), or in methyl cellulose (MS-Bup.MC) were compared with their respective drug-free controls (placebos).

RESULTS

Serum bupivacaine reached a maximal average value (n = 8) of 194.9 ng/mL at 8 hours after injection of MS-Bup (95% upper prediction limit = 230.2 ng/mL), compared with the maximal average (n = 6) serum level of 374.9 ng/mL (95% prediction limit = 470.6 ng/mL) at 30 minutes after injection of BupHCl. Serum bupivacaine decreased to undetectable levels (<3.23 ng/mL) at 8 hours after BupHCl and was detectable at approximately 20% of the maximal value at 144 hours after MS-Bup injection. BupHCl injection resulted in moderate lymphocytic infiltration of skeletal muscle at 1 and 3 days. MS-Bup.CMC and placebo-CMC caused extensive infiltration of macrophages, lymphocytes, and some neutrophils at 1 to 7 days, whereas MS-Bup.MC and placebo-MC caused only mild inflammation.

CONCLUSIONS

Subcutaneous administration of microspheres releasing bupivacaine results in lower blood levels lasting for much longer times than those from bupivacaine solution.