Toxicity of bupivacaine encapsulated into liposomes and injected intravenously: comparison with plain solutions

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.

Robust gelatin hydrogels for local sustained release of bupivacaine following spinal surgery

Adequate treatment of pain arising from spinal surgery is a major clinical challenge. Opioids are the mainstay of current treatment methods, but the frequency and severity of their side effects display a clear need for opioid-free analgesia. Local anesthetics have been encapsulated into sustained-release drug delivery systems to provide postoperative pain relief. However, these formulations are limited by rapid diffusion out of the surgical site. To overcome this limitation, we synthesized ring-shaped hydrogels incorporating bupivacaine, designed to be co-implanted with pedicle screws during spinal surgery. Hydrogels were prepared by riboflavin-mediated crosslinking of gelatin functionalized with tyramine moieties. Additionally, oxidized β-cyclodextrin was introduced into the hydrogel formulation to form dynamic bonds with tyramine functionalities, which enables self-healing behavior and resistance to shear. Feasibility of hydrogel implantation combined with pedicle screws was qualitatively assessed in cadaveric sheep as a model for instrumented spinal surgery. The in-situ crystallization of bupivacaine within the hydrogel matrix provided a moderate burst decrease and sustained release that exceeded 72 hours in vitro. The use of bupivacaine crystals decreased drug-induced cytotoxicity in vitro compared to bupivacaine HCl. Thus, the presented robust hydrogel formulation provides promising properties to enable the stationary release of non-opioid analgesics following spinal surgery. STATEMENT OF SIGNIFICANCE: Currently, postoperative pain following spinal surgery is mainly treated with opioids. However, the use of opioids is associated with several side effects including addiction. Here we developed robust and cytocompatible gelatin hydrogels, prepared via riboflavin-mediated photocrosslinking, that can withstand orthopedic implantation. The implantability was confirmed in cadaveric instrumented spinal surgery. Further, hydrogels were loaded with bupivacaine crystals to provide sustained release beyond 72 hours in vitro. The use of crystallized bupivacaine decreased cytotoxicity compared to bupivacaine HCl. The present formulation can aid in enabling opioid-free analgesia following instrumented spinal surgery.

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.

Effects of intraoperative liposomal bupivacaine on pain control and opioid use after pediatric Chiari I malformation surgery: an initial experience

OBJECTIVE

Pediatric Chiari I malformation decompression is a common neurosurgical procedure. Liposomal bupivacaine (LB) is a novel formulation that can have an impact on postoperative recovery for particular procedures, but its potential role in pediatric neurosurgery is largely unexplored. The authors sought to describe and assess their initial experience with LB in pediatric Chiari I malformation decompression to better define its potential role as an analgesic agent in a procedure for which the postoperative course is often remarkably painful.

METHODS

A retrospective review of all pediatric Chiari procedures performed at the authors' institution between 2018 and 2020 was conducted. Patients were divided into those who were treated with a single intraoperative dose of LB (LB group) and those who were not (control group). Comparisons of total opioid use and pain control were made using chi-square and Wilcoxon rank-sum tests.

RESULTS

A total of 18 patients were identified, 9 (50%) in the LB group and 9 (50%) in the control group. Overall, there were 13 (72%) female and 5 (28%) male patients with a mean age of 15.9 years. No surgical complications were observed over a mean length of stay of 2.7 days. Within the first 24 hours after surgery, the LB group had significantly lower total opioid use than the control group (17.5 vs 47.9 morphine milligram equivalents, respectively; p = 0.03) as well as lower mean pain scores reported by patients using a 10-point visual analog scale (3.6 vs 5.5 for the LB vs control groups, p = 0.04). However, from the first 24 postoperative hours to discharge, total opioid use (p = 0.51) and mean pain scores (p = 0.09) were statistically comparable between the two groups. There were 2/9 (22%) LB patients versus 0/9 (0%) control patients who did not require opioid analgesia at any point during hospitalization.

CONCLUSIONS

The use of a single intraoperative dose of LB in pediatric Chiari I malformation surgery appears to be safe and has the potential to reduce pain scores and opioid use when administered during the first 24 postoperative hours. From that time period to discharge, however, there may be no significant difference in total opioid use or pain scores.

Epicardial Interventions: Impact of Liposomal Bupivacaine on Postprocedural Management (The EPI-LIBRE Study)

Background:

Electrophysiological procedures such as epicardial ventricular tachycardia ablation and Lariat left atrial appendage ligation that involve the epicardial space are typically associated with significant postoperative pain due to mechanical irritation and associated inflammation. There is an unmet need for an effective pain management strategy in this group of patients. We studied how this impacts patient comfort and duration of hospitalization and other associated comorbidities related to pericardial access.

Methods:

This is a multicenter retrospective study including 104 patients who underwent epicardial ventricular tachycardia ablation and Lariat left atrial appendage exclusion. We compared 53 patients who received postprocedural intrapericardial liposomal bupivacaine (LB)+oral colchicine (LB group) and 51 patients who received colchicine alone (non-LB group) between January 2015 and March 2018.

Results:

LB was associated with significant lowering of median pain scale at 6 hours (1.0 [0–2.0] versus 8.0 [6.0–8.0], P <0.001), 12 hours (1.0 [1.0–2.0] versus 6.0 [5.0–6.0], P <0.001), and up to 48 hours postprocedure. Incidence of acute severe pericarditis delayed pericardial effusion and gastrointestinal adverse effects were similar in both groups. Median length of stay was significantly lower in LB group (2.0 versus 3.0; adjusted linear coefficient −1 [CI −1.3 to −0.6], P <0.001). Subgroup analysis demonstrated similar favorable outcomes in both Lariat and epicardial ventricular tachycardia ablation groups.

Conclusions:

Addition of intrapericardial postprocedural LB to oral colchicine in patients undergoing epicardial access during ventricular tachycardia ablation or Lariat procedure is associated with significantly decreased numeric pain score up to 48 hours compared with colchicine alone. It is also associated with significantly shorter length of hospital stay without an increase in the risk of adverse events.

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.

Drug delivery systems for prolonged duration local anesthesia

Numerous drug delivery systems have been applied to the problem of providing prolonged duration local anesthesia (PDLA). Here we review the rationale for PDLA, the desirable features for and important attributes of such systems, and specific examples that have been developed.

The effect of two drug delivery systems in ropivacaine cytotoxicity and cytokine release by human keratinocytes and fibroblasts

Objectives

Modified drug delivery systems have been developed to improve pharmacological properties of local anaesthetics. However, the inflammatory potential of these formulations was not investigated. This study compared the in-vitro effects of ropivacaine (ropi) in plain, liposomal (MLV) or 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) formulations on cell viability, apoptosis and cytokine (IL-1α, TNF-α, IL-6 and IL-10) release.

Methods

Human immortalized keratinocytes (HaCaT) and human immortalized gingival fibroblasts (HGF) were exposed to 1–100 μm ropi concentrations. The cell viability was measured by XTT and LIVE/DEAD assay. Apoptosis was performed by flow cytometry, and cytokine release was measured by ELISA assay.

Key findings

Human immortalized keratinocyte viability was reduced by ropi and both drug delivery systems. However, none of the formulations induced apoptosis. Results showed a differential regulation of IL-1α TNF-α, IL-6 and IL-10 by HaCaT and HGF. Ropi-HP-β-CD increased twofold the IL-6 release by HGF in comparison with the control, while 100 μm ropi-MLV led to an increased release of all pro-inflammatory cytokines by HGF.

Conclusion

The loss in cell viability was not related to cellular apoptosis. Ropi complexed with HP-β-CD showed a similar cytokine release pattern when compared to the plain formulation. Thus, the HP-β-CD form was a better drug carrier than the MLV form for ropivacaine drug delivery.

Femoral and sciatic nerve blockades and incision site infiltration in rabbits undergoing stifle joint arthrotomy

This study was designed to determine whether perineural injections of local anaesthetics decreases intraoperative nociception and improves postoperative analgesia in New Zealand White rabbits undergoing experimental stifle arthrotomy. All animals were anaesthetized using isoflurane and received morphine intramuscularly. The sciatic and femoral nerves of the leg to be operated on were located using a nerve stimulator (1 Hz, 0.5 mA). Rabbits were assigned to a treatment group (LB; n = 12) or a placebo group (P; n = 12) in a randomized blinded fashion. Group LB received lidocaine 2% (1 mg/kg) combined with bupivacaine 0.5% (0.25 mg/kg) injections around the sciatic and femoral nerves (0.1 mL/kg total volume per site) and subcutaneous infiltration of the incision site with lidocaine 1% (1.25 mg/kg). Group P received the same volume of 0.9% NaCl. Rabbits in group P required higher doses of intraoperative fentanyl and propofol to reduce heart rate and suppress increase in systolic blood pressure, and maintain an adequate anaesthetic plane. Interventional analgesia (buprenorphine and carprofen) was required significantly earlier in rabbits in group P (2 and 6 h after the first nerve blockade, respectively) based on assessment of their pain-related behaviour and range of motion. Using a visual analogue scale (0 mm= no pain to 100 mm= maximal possible pain), rabbits in group LB were judged to show significantly less pain compared with rabbits in group P (14 ± 10 mm and 37 ± 25 mm, respectively) 2 h after nerve blockade. In conclusion, this technique of perineural analgesia combined with incision site infiltration reduced intraoperative fentanyl requirements and improved postoperative analgesia in rabbits.

Release Pattern of Liposomal Bupivacaine in Artificial Cerebrospinal Fluid

OBJECTIVE

We aimed to compare the possible controlled release profile of multilamellar liposomal bupivacaine formulations with non-liposomal forms in artificial cerebrospinal fluid (CSF) under in vitro conditions.

METHODS

Liposome formulations were prepared using a dry-film hydration method. Then, an artificial CSF-buffered solution was prepared. Bupivacaine base with liposomal bupivacaine base, bupivacaine HCl with liposomal bupivacaine HCl and bupivacaine HCl were added in a Franz diffusion cell. These solutions were kept in a hot water bath for 24 h. The samples were taken at 0.5, 1, 3, 6, 12 and 24 h (1st series of experiment). Solutions of bupivacaine base with liposomal bupivacaine base and bupivacaine HCl with liposomal bupivacaine HCl were centrifuged to obtain liposomal bupivacaine base and liposomal bupivacaine HCl. Afterwards, liposomal bupivacaine base and liposomal bupivacaine HCl were added in a Franz diffusion cell. After keeping these solutions in a hot water bath for 24 h as well, the samples were taken at the same time intervals (2(nd) series of experiment). All samples (54 from the 1st experiment and 36 from the 2(nd) experiment) were analysed with high-performance liquid chromatography and ultra-performance liquid chromatography and their chromatograms were obtained.

RESULTS

After obtaining calibration curves for bupivacaine base and HCl, release patterns of these formulations were plotted. A markedly controlled slow-release pattern was observed for multilamellar liposomal bupivacaine than for non-liposomal bupivacaine in artificial CSF.

CONCLUSION

Demonstration of controlled slow-release profile for mutilamellar liposomal bupivacaine in artificial CSF in vitro might support intrathecal use of liposomal bupivacaine in vivo in animal studies.

Anaesthetic efficacy of unilamellar and multilamellar liposomal formulations of articaine in inflamed and uninflamed tissue

We compared the efficacy of articaine encapsulated in multilamellar and unilamellar liposomes with that of articaine with epinephrine, after infiltration into inflamed and uninflamed tissue in rats. We encapsulated 4% articaine in multilamellar (articaine:multi) and unilamellar (articaine:uni) liposomes and compared them with 4% articaine with 1:100 000 epinephrine (articaine:epinephrine), in inflamed (plantar incision into the hind paw) and uninflamed (infraorbital nerve block) tissue in rats. Anaesthetic formulations (0.1ml) were injected near the right infraorbital foramen in uninflamed tissue, where success and duration of anaesthesia were assessed by pinching the upper lip every 5 minutes. For inflamed tissue the anaesthetic formulations (0.1ml) were injected laterally into a surgical wound made 24 hours earlier in the plantar region of the rat's right hind paw. The degree of anaesthesia was assessed by application of forces laterally to the wound with electronic von Frey filaments. Articaine:uni resulted in less successful anaesthesia than both articaine:multi (p=1.1x10(-5)) and articaine:epinephrine (p=4.3x10(-8)) in uninflamed tissue, but there were no differences in duration or success of anaesthesia between articaine:epinephrine and articaine:multi. In inflamed tissue articaine:epinephrine gave significantly more effective anaesthesia for longer than articaine:uni (p=2.3x10(-6)), and articaine:epinephrine (p=1.8x10(-6)) formulations, which did not differ from each other. Multilamellar liposomal articaine could be an option for local anaesthesia in uninflamed tissues. However, articaine with epinephrine gave better results than liposomal formulations in inflamed tissue.

Liposomal lidocaine gel for topical use at the oral mucosa: characterization, in vitro assays and in vivo anesthetic efficacy in humans

OBJECTIVE

To characterize liposomal-lidocaine formulations for topical use on oral mucosa and to compare their in vitro permeation and in vivo anesthetic efficacy with commercially available lidocaine formulations.

MATERIALS AND METHODS

Large unilamellar liposomes (400 nm) containing lidocaine were prepared using phosphatidylcholine, cholesterol, and α-tocoferol (4:3:0.07, w:w:w) and were characterized in terms of membrane/water partition coefficient, encapsulation efficiency, size, polydispersity, zeta potential, and in vitro release. In vitro permeation across pig palatal mucosa and in vivo topical anesthetic efficacy on the palatal mucosa in healthy volunteers (double-blinded cross-over, placebo controlled study) were performed. The following formulations were tested: liposome-encapsulated 5% lidocaine (Liposome-Lido5); liposome-encapsulated 2.5% lidocaine (Liposome-Lido2.5); 5% lidocaine ointment (Xylocaina®), and eutectic mixture of lidocaine and prilocaine 2.5% (EMLA®).

RESULTS

The Liposome-Lido5 and EMLA showed the best in vitro permeation parameters (flux and permeability coefficient) in comparison with Xylocaina and placebo groups, as well as the best in vivo topical anesthetic efficacy.

CONCLUSION

We successfully developed and characterized a liposome encapsulated 5% lidocaine gel. It could be considered an option to other topical anesthetic agents for oral mucosa.

Liposomal-benzocaine gel formulation: correlation between in vitro assays and in vivo topical anesthesia in volunteers

The aim of the present study was to characterize a liposome-based benzocaine (BZC) formulation designed for topical use on the oral mucosa and to evaluate its in vitro retention and permeation using the Franz-type diffusion cells through pig esophagus mucosa. To predict the effectiveness of new designed formulations during preclinical studies, a correlation between in vitro assays and in vivo efficacy was performed. Liposomal BZC was characterized in terms of membrane/water partition coefficient, encapsulation efficiency, size, polydispersity, zeta potential, and morphology. Liposomal BZC (BL10) was incorporated into gel formulation and its performances were compared to plain BZC gel (B10) and the commercially available BZC gel (B20). BL10 and B10 presented higher flux and retention on pig esophagus mucosa with a shorter lag time, when compared to B20. BZC flux was strongly correlated with in vivo anesthetic efficacy, but not with topical anesthesia duration. The retention studies did not correlate with any of the in vivo efficacy parameters. Thus, in vitro permeation study can be useful to predict anesthetic efficacy during preclinical tests, because a correlation between flux and anesthetic efficacy was observed. Therefore, in vitro assays, followed by in vivo efficacy, are necessary to confirm anesthetic performance.

Extended release formulations for local anaesthetic agents

Systemic toxicity through overdose of local anaesthetic agents is a real concern. By encapsulating local anaesthetics in biodegradable carriers to produce a system for prolonged release, their duration of action can be extended. This encapsulation should also improve the safety profile of the local anaesthetic as it is released at a slower rate. Work with naturally occurring local anaestheticss has also shown promise in the area of reducing systemic and neurotoxicity. Extended duration local anaesthetic formulations in current development or clinical use include liposomes, hydrophobic based polymer particles such as Poly(lactic-co-glycolic acid) microspheres, pasty injectable and solid polymers like Poly(sebacic-co-ricinoleic acid) P(SA:RA) and their combination with synthetic and natural local anaesthetic. Their duration of action, rationale and limitations are reviewed. Direct comparison of the different agents is limited by their chemical properties, the drug doses encapsulated and the details of in vivo models described.

Local anesthetic systemic toxicity: prevention and treatment

Anesthesia is a sine qua non for most surgeries. Like any medical advance, progress in regional anesthesia has not come without its share of complications, including a spectrum extending from localized nerve injury to systemic cardiovascular toxicity and death. This article discusses the mechanisms and clinical presentation, prevention, treatment, and future trends of local anesthetic systemic toxicity. The adverse effects of lipid emulsion therapy are also included.

Review of prolonged local anesthetic action

IMPORTANCE OF THE FIELD

Pain following surgery is often treated by local anesthetic agents. Duration of the analgesia can be extended safely following administration of encapsulated large doses of local anesthetic agents.

AREAS COVERED IN THIS REVIEW

This review considers formulations used for encapsulation of local anesthetic agents for prolonged anesthesia effect. All studies describing encapsulation of a commercial local anesthetic agent for providing prolonged analgesia were considered using the NCBI Medline site. of local anesthetic, prolonged anesthesia, polymers and liposomes were entered in order to retrieve appropriate articles and reviews from 1966 to 2010, with emphasis on the last 10 years. Reference pages were searched manually for other relevant articles. The topics covered include an overview of local anesthetic agents and a review of local anesthetic carrier agents, with emphasis on liposomes and polymer carriers. Articles were limited to the English language.

WHAT THE READER WILL GAIN

The current research areas for prolongation of local anesthetic effect are evaluated, along with their limitations. Each topic has been summarized, and the review has attempted to cover all current laboratory and clinical studies in a simple manner that should also be useful for readers without a pharmacology background. The direction of research is promising and exciting, and this review should be a useful up-to-date reference.

TAKE HOME MESSAGE

Many formulations including polymer and liposome carriers have facilitated prolonged local anesthetic action for several days, although few clinical studies have been performed. This field promises a safe way to deliver local anesthetics for effect far beyond that of commercially available agents, with potential cost and health benefits for patients suffering chronic or postoperative pain.

Liposomal encapsulation improves the duration of soft tissue anesthesia but does not induce pulpal anesthesia

STUDY OBJECTIVE

To compare the topical and the pulpal anesthesia efficacy of liposomal and plain benzocaine formulations.

DESIGN

Double-blinded, randomized crossover study.

SETTING

University ambulatory dental center.

PATIENTS

30 ASA physical status I volunteers.

INTERVENTIONS

Volunteers received, in three different sessions, topical application of liposome-encapsulated 10% benzocaine (LB10), 10% benzocaine gel (B10), and 20% benzocaine gel (B20) in the right maxillary canine mucobuccal fold.

MEASUREMENTS

Pain associated with the needle insertion was rated by visual analog scale (VAS) and the duration of topical anesthesia was recorded. Pulpal anesthesia was evaluated using an electric pulp tester.

MAIN RESULTS

VAS values (median, 1st - 3rd quartiles) were 17 cm (11 - 25), 14 cm (3 - 22), and 21 cm (9 - 21) for B10, LB10, and B20, respectively. No differences were noted among the groups (Friedman test; P = 0.58). Soft tissue anesthesia was also not different. The LB10 [10 (8 - 12) min] showed longer soft tissue anesthesia (Friedman test; P < 0.01) than the other agents [B10 = 8 (5 - 10) min, and B20 = 7 (6 - 9) min]. None of the topical benzocaine formulations tested induced pulpal anesthesia.

CONCLUSIONS

The encapsulation of benzocaine into liposome increased the duration of soft tissue anesthesia. However, it did not induce pulpal anesthesia.

Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine

This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and α-tocopherol (4:3:0.07, mole%). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVCPLAIN) and liposomal RVC (RVCLUV) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 ± 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P &lt; 0.001) from liposomes. RVCLUV presented reduced cytotoxicity (P &lt; 0.001) when compared with RVCPLAIN. Treatment with RVCLUV increased the duration (P &lt; 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4–1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVCPLAIN. Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVCPLAIN or RVCluv at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVCLUV as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

Bupivacaine binding to pegylated liposomes

BACKGROUND

Local anesthetic drugs, such as bupivacaine, can cause severe toxicity. Lipid emulsions have been proposed and used clinically for treating such cases. Liposomes may be an alternative for overdose treatment because of their unique structures and surface charges, which allows them to act as high affinity drug "sinks" and remove bupivacaine from solution.

METHODS

We conducted in vitro experiments with unilamellar and multilamellar anionic, polymer-coated liposomes to determine the amount of bupivacaine bound to liposomes in buffer solutions as a means of assessing the liposome-drug affinity. Binding experiments were also done in human serum to determine the liposomes' ability to compete with serum proteins for binding drug molecules.

RESULTS

Unilamellar liposomes sequestered 60%-65% and 77%-85% of bupivacaine from buffer at 1.45 and 2.9 mg lipid/mL, respectively. The increased lipid loading increased the drug uptake at all drug concentrations measured (P = 0.001, 0.002, <0.001, and 0.003 for 5, 20, 35, and 50 microM, respectively). Multilamellar liposomes bound more drug per unit mass, with 71%-90% of the total bupivacaine bound at a phospholipid concentration of 1.45 mg lipid/mL. When comparing unilamellar and multilamellar liposomes at 1.45 mg lipid/mL, the multilamellar liposomes were significantly better at 3 of the 4 drug concentrations measured (P = 0.002, 0.001, 0.001, and 0.08 for 5, 20, 35, and 50 microM, respectively). In human serum samples, unilamellar liposomes (2.9 mg lipid/mL) reduced the unbound (free) drug by 36% (P = 0.037), 56% (P = 0.022), 47% (P = 0.042), and 50% (P = 0.018) for bupivacaine concentrations of 5, 20, 35, and 50 microM, respectively.

CONCLUSIONS

The anionic, pegylated liposomes exhibit high binding for bupivacaine, both in buffer and in human serum. These results suggest that an IV injection of liposomes could be useful for the treatment of bupivacaine toxicity through drug redistribution.

Stability and local toxicity evaluation of a liposomal prilocaine formulation

This study reports a physicochemical stability evaluation of a previously reported liposomal prilocaine (PLC(LUV)) formulation (Cereda et al. J. Pharm. Pharmaceut. Sci. 7:235, 2004) before and after steam sterilization as well as its local toxicity evaluation. Prilocaine (PLC) was encapsulated into extruded unilamellar liposomes (LUVs) composed by egg phosphatidylcholine:cholesterol:alfa-tocopherol (4:3:0.07, mole %). Laser light-scattering analysis (p > 0.05) and thiobarbituric acid reaction (p > 0.05) were used to evaluate the liposomes physical (size) and chemical (oxidation) stability, respectively. The prilocaine chemical stability was followed by (1)H-nuclear magnetic resonance. These tests detected no differences on the physicochemical stability of PLC or PLC(LUV), sterilized or not, up to 30 days after preparation (p > 0.05). Finally, the paw edema test and histological analysis of rat oral mucosa were used to assess the possible inflammatory effects of PLC(LUV). PLC(LUV) did not evoke rat paw edema (p > 0.05), and no significant differences were found in histological analysis, when compared to the control groups (p > 0.05). The present work shows that PLC(LUV) is stable for a 30-day period and did not induce significant inflammatory effects both in the paw edema test and in histological analysis, giving supporting evidence for its safety and possible clinical use in dentistry.

Liposome-encapsulated ropivacaine for topical anesthesia of human oral mucosa

BACKGROUND

The elimination of pain caused by needle insertion for local anesthesia would be a significant advance in dentistry.

METHODS

In this blinded cross-over study we evaluated the efficacy of liposome-encapsulated ropivacaine for topical anesthesia. Thirty healthy volunteers received 60 mg topical anesthetics: Liposome-encapsulated 1% ropivacaine, 1% plain ropivacaine, 2.5% lidocaine and 2.5% prilocaine mixture (EMLA), and 20% benzocaine gel, in the buccal fold of the upper-right canine for 2 min in different sessions. After insertion of 30-G needles, pain was rated on a visual analog scale (VAS). A pinprick test was used to measure the duration of topical anesthesia. The pulpar response was assessed by an electric pulp tester.

RESULTS

VAS median and interquartile range (in cm) were 0.8 (0.4-1.5), 1.6 (0.8-2.6), 1.1 (0.3-2.7), 2.2 (0.9-2.9) for liposome-encapsulated ropivacaine, ropivacaine, EMLA, and benzocaine groups, respectively. The liposome-encapsulated ropivacaine group showed lower VAS mean values when compared with the benzocaine group (P = 0.0205). The median values and interquartile range for the duration of soft tissue anesthesia were 11 (7-14), 6.5 (4-11), 14 (11-16), and 7 (6-9) min for liposome-encapsulated ropivacaine, ropivacaine, EMLA, and benzocaine groups, respectively. EMLA and liposome-encapsulated ropivacaine were just as efficient for reducing pain, and showed longer soft tissue anesthesia when compared to the other local anesthetics (P = 0.0001).

CONCLUSION

Liposomal-encapsulated 1% ropivacaine gel was equivalent to EMLA for reducing pain during needle insertion and for the duration of soft tissue anesthesia. None of the topical anesthetics was effective for inducing pulpal anesthesia.

Encapsulation of mepivacaine prolongs the analgesia provided by sciatic nerve blockade in mice

PURPOSE

Liposomal formulations of local anesthetics (LA) are able to control drug-delivery in biological systems, prolonging their anesthetic effect. This study aimed to prepare, characterize and evaluate in vivo drug-delivery systems, composed of large unilamellar liposomes (LUV), for bupivacaine (BVC) and mepivacaine (MVC).

METHODS

BVC and MVC hydrochloride were encapsulated into LUV (0.4 micro m) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07 molar ratio) to final concentrations of 0.125, 0.25, 0.5% for BVC and 0.5, 1, 2% for MVC. Motor function and antinociceptive effects were evaluated by sciatic nerve blockade induced by liposomal and plain formulations in mice.

RESULTS

Liposomal formulations modified neither the intensity nor the duration of motor blockade compared to plain solutions. Concerning sensory blockade, liposomal BVC (BVC(LUV)) showed no advantage relatively to the plain BVC injection while liposomal MVC (MVC(LUV)) improved both the intensity (1.4-1.6 times) and the duration of sensory blockade (1.3-1.7 times) in comparison to its plain solution (P < 0.001) suggesting an increased lipid solubility, availability and controlled-release of the drug at the site of injection.

CONCLUSION

MVC(LUV) provided a LA effect comparable to that of BVC. We propose MVC(LUV) drug delivery as a potentially new therapeutic option for the treatment of acute pain since the formulation enhances the duration of sensory blockade at lower concentrations than those of plain MVC.

Kinetic and dynamic studies of liposomal bupivacaine and bupivacaine solution after subcutaneous injection in rats

The pharmacodynamics and pharmacokinetics of bupivacaine in solution and in liposome preparations following subcutaneous administration were studied in rats. Multilamellar vesicles entrapping bupivacaine solution were prepared. The local anaesthetic effect was estimated by the tail-flick test in Wistar rats treated with 1 mg bupivacaine in 0.2-mL preparations. Plasma concentrations of bupivacaine were determined by high-performance liquid chromatography. The results showed that both bupivacaine solution and bupivacaine liposomes revealed local anaesthetic effects in the initial tail-flick test (15 min after injection). With bupivacaine liposomes, the duration of action was 5-fold (447+/-28.9 vs 87+/-6.7 min), the maximum possible effect was 2-fold (100+/-0 vs 47.6+/-13%), and the peak plasma concentration (Cmax) was less than one-fifth (0.12+/-0.04 vs 0.65+/-0.04 microg mL(-1)) that with bupivacaine solution. The sensory block effect of bupivacaine solution completely resolved at 90 min, while the plasma concentration of bupivacaine was still more than half the Cmax. Bupivacaine liposomes resulted in a low and relatively constant plasma level (approx. 0.1 microg mL(-1)) and a pronounced local anaesthetic effect throughout the experimental period (> 7 h). In conclusion, bupivacaine liposomes elevated the intensity and prolonged the duration of the local anaesthetic effect of bupivacaine, and suppressed the systemic absorption rate of encapsulated bupivacaine.

The Holy Grail: long-acting local anaesthetics and liposomes

The ability to provide an extended duration of analgesia of days following a single injection without the need for catheters, pumps and infusion systems would be a great benefit in acute and chronic pain. Exciting progress is being made in our ability to combine local anaesthetics with liposomes and polymer microspheres. These interesting formulations in animal models have allowed up to 4 days of analgesia. Their use clinically will be a great advance which could possibly occur in the near future.

DRV liposomal bupivacaine: preparation, characterization, and in vivo evaluation in mice

PURPOSE

To evaluate the dehydration-rehydration technique to prepare a formulation of liposomal bupivacaine, and to assess its analgesic efficacy.

METHODS

Bupivacaine hydrochloride (BUP) was encapsulated into dehydration-rehydration vesicles (DRV) of varying phospholipid (PL) compositions. Two bilayer-forming phospholipids were used, the "fluid" dimyristoyl-phosphatidylcholine and the "solid" distearoyl-phosphatidylcholine (DSPC), with 20 or 40 mol% cholesterol, in the presence of bupivacaine at a 1.28 or 0.64 BUP/PL mole ratio. After rehydration, drug/lipid ratios were determined. The formulation with the highest drug/lipid ratio (DSPC/cholesterol in an 8:2 mole ratio prepared in the presence of bupivacaine in a 1.28 BUP/PL mole ratio) was adjusted to a final bupivacaine concentration of 3.5% or 0.5%. The duration of skin analgesia after subcutaneous injection in mice produced by these formulations was compared with the conventional administration of a plain 0.5% solution of BUP. In addition, the concentration of residual bupivacaine at the injection site was followed for 96 h.

RESULTS

The relatively low organic solvent/aqueous phase and membrane/aqueous phase partition coefficients, together with liposomal trapped volume and BUP/PL mole ratio, indicated that most of the drug was encapsulated in the intraliposome aqueous phase of the DRV. The DSPC/cholesterol 8:2 mole ratio had the best drug encapsulation (BUP/PL = 0.36). Compared to plain BUP, these BUP-DRV produced significant prolongation of analgesia, which is explained by longer residence time of the drug at the site of injection.

CONCLUSIONS

Bupivacaine-DRV may have a role in achieving safe, effective, and prolonged analgesia in humans.

Prolongation of epidural anaesthesia in dogs with bupivacaine in a lipid emulsion

An aqueous solution and a lipid emulsion of bupivacaine were administered epidurally in doses of 1.8 mg/kg to six beagle dogs following a randomised two-phase crossover design. The aqueous solution was absorbed rapidly and the mean (sd) peak venous plasma concentration of bupivacaine, 1.4 (0.4) microg/ml, was detected after five minutes. After administration of the lipid emulsion, the peak plasma concentration of bupivacaine, 0.6 (0.2) microg/ml, was detected after 30 minutes. The mean (sd) t1/2beta of the aqueous preparation was 149.1 (32.6) minutes, and of the lipid emulsion 119.2 (34.0) minutes. Both preparations had a similar bioavailability. The mean time to the onset of motor block after the administration of the aqueous solution, 2.3 (2.2) minutes, was significantly shorter (P=0.028) than after the administration of the lipid emulsion, 9.4 (1.9) minutes, and the duration of the motor block induced by the lipid emulsion, 217.6 (26.2) minutes, was significantly longer (P=0.043) than for the aqueous solution, 158 (48.8) minutes. During anaesthesia, the plasma concentrations of bupivacaine ranged between 1.3 and 0.2 microg/ml. Non-significant changes in systolic blood pressure and heart rate were observed which coincided with the peak plasma concentrations of bupivacaine.

The effects of intrathecal morphine encapsulated in L- and D-dipalmitoylphosphatidyl choline liposomes on acute nociception in rats

Liposomes can serve as a sustained-release carrier system, permitting the spinal delivery of large opioid doses restricting the dose for acute systemic uptake. We evaluated the antinociceptive effects of morphine encapsulated in liposomes of two isomeric phospholipids, L-dipalmitoylphosphatidyl choline (L-DPPC) and D-dipalmitoylphosphatidyl choline (D-DPPC), in comparison with morphine in saline. Sprague-Dawley rats with chronic lumbar intrathecal catheters were tested for their acute nociceptive response using a hindpaw thermal escape test. Their general behavior, motor function, pinna reflex, and corneal reflex were also examined. The duration of antinociception was longer in both liposomal morphine groups than in the free morphine group. The peak antinociceptive effects were observed within 30 min after intrathecal morphine, L-DPPC or D-DPPC morphine injection. The rank order of the area under the effect-time curve for antinociception was L-DPPC morphine > D-DPPC morphine > morphine. The 50% effective dose was: 2.7 microg (morphine), 4.6 microg (L-DPPC morphine), and 6.4 microg (D-DPPC morphine). D-DPPC morphine had less side effects for a given antinociceptive AUC than morphine. In conclusion, L-DPPC and D-DPPC liposome encapsulation of morphine prolonged the antinociceptive effect on acute thermal stimulation and could decrease side effects, compared with morphine alone.

IMPLICATIONS

Two isomers of liposome (L-dipalmitoylphosphatidyl choline and D-dipalmitoylphosphatidyl choline) encapsulation of morphine prolonged the analgesic effect on acute thermal-induced pain when administered intrathecally and could decrease side effects, compared with morphine alone.

A dose-response study of epidural liposomal bupivacaine in rabbits

Liposomes are drug delivery systems used to prolong local effects of bupivacaine. We studied the relationships between motor and hemodynamic changes and epidural doses of plain bupivacaine (P) and liposomal bupivacaine (L) in rabbits equipped with chronical lumbar epidural and femoral arterial catheters. Liposomal (phosphatidylcholine-cholesterol) suspensions contained 20 mg ml-1 of lipid, and different doses of bupivacaine (Lipo 7.5=7.5-; Lipo 3.7=3. 75-; Lipo 2.5=2.5-; Lipo 1.2=1.25-; and Lipo 0.7=0.65-mg of bupivacaine per ml). Forty rabbits were randomly assigned to five groups to receive epidural anesthesia (1 ml) as follows: Groups I to V received 0.65 to 7.5 mg of bupivacaine as P then as L. Release rate of bupivacaine from liposome was significantly slower using Lipo 3.7 than after Lipo 2.5 (Td was 3.9 h and 1.7 h respectively). Increasing the doses of L and P resulted in faster onset time for complete motor blockade and in a prolonged duration of motor effects. Liposomal formulation appears to be a powerful delivery system to prolong the motor effects of bupivacaine since E50 was lower and Emax higher than after the use of plain solution (E50 4.49+/-1.81 mg and Emax 152+/-40 min for P; and E50 2.61+/-0.23 mg and Emax 202+/-9 min for L). Hemodynamic changes were linearly related to doses of bupivacaine injected. The best bupivacaine-to-lipid ratio to prolong motor effects using our model was 3.75 mg and 20.0 mg respectively (Lipo 3.7).

Novel Drug Delivery Systems

Interest in pain management is growing, with the emerging demand by our patients and colleagues, for pain relief. To meet that need, pharmaceutical and medical technology companies have provided the medical field with a variety of choices and options to deliver medication for pain control. Examination and review of the present systemic options are introduced. A more detailed look at the intrathecal route is necessary because of the tremendous potential for receptor-targeted drug delivery. The ability to treat nociceptive and neuropathic pain with drug-specific therapy makes this system all the more exciting. Because of this future, a wealth of new and old drugs are being found or reexamined for their use.

Wound infiltration with liposomal bupivacaine prolongs analgesia in rats

BACKGROUND

Wound infiltration with local anesthetics does not reliably produce satisfactory postoperative analgesia, and the dose of local anesthetic which may be safely administered is limited by the potential for systemic toxicity. This study evaluated the efficacy of a slow-release liposomal bupivacaine formulation on duration of wound analgesia.

METHODS

Multilammelar liposomes containing bupivacaine were assessed using a rat paw wound model. Twenty-four hours after surgical incision, paw wounds determined to be hyperalgesic to graded force testing with von Frey hairs were infiltrated with 0.3 ml of 2% liposomal bupivacaine, 0.5% plain bupivacaine, saline, or "empty' (normal saline) liposomes (n = 6/group). The duration of analgesia was measured. The 0.5% plain concentration was chosen because, in preliminary experiments, larger doses were often fatal. Analgesia duration was compared using Mann-Whitney U test at P < 0.05. In other rats, plasma bupivacaine levels after wound infiltration with either 2% liposomal formulation or 0.5% plain formulation were assessed (n = 8/group).

RESULTS

The mean duration of analgesia was 23 +/- 3 (SD) min for plain bupivacaine and 180 +/- 30 min for liposomal bupivacaine. No wound analgesia was detected in animals given normal saline or "empty' liposomes. Plasma bupivacaine levels tended to be lower after liposomal than plain bupivacaine.

CONCLUSIONS

The 8-fold increase in duration of wound analgesia and the lower plasma levels seen with the liposomal formulation are explained by gradual drug release from the liposomal depot. These results may have important implications for achieving safe and effective analgesia with wound infiltration techniques in humans.

Use of liposome-associated bupivacaine in a cancer pain syndrome

Bupivacaine 0.25% encapsulated by multilamellar liposomes was administered epidurally to a patient suffering pain associated with lung cancer and the effect compared with a plain bupivacaine solution of the same concentration. Complete analgesia was produced for 4 h with the plain solution and 11 h with the liposomal formulation. No motor blockade or haemodynamic instability was observed with the liposome-associated bupivacaine.

Antinociception and side effects of L- and D-dipalmitoylphosphatidyl choline liposome-encapsulated alfentanil after spinal delivery in rats

We have observed that spinal liposome administration in the rat resulted in in an allodynia evoked by light touch. We later determined that liposomes composed of D-isomer phospholipids were essentially non-toxic. This study examines the effects of alfentanil encapsulated in liposomes made from the natural L-isomer and synthetic D-isomer of dipalmitoyl phosphatidyl choline on antinoceiception, side effects, and algogenic behaviour. Both unilamellar and multilamellar liposomes were studied. Rats prepared with chronic intrathecal catheters received intrathecal injections of alfentanil (5 or 50 micrograms) in saline or encapsulated in liposomes composed of either L- or D-isomers of dipalmitoyl phosphatidyl choline (DPPC) in unilamellar or multilamellar liposome formulations. Antinociception was measured using the hot plate test (52.5 degrees). Side effects were measured by catalepsy, corneal responses, pinna response, righting reflex, and paw step. Allodynia was measured by lightly stroking the animal's back. Intrathecal alfentanil in saline or in the liposomes produced a dose-dependent increased latency in the hot plate response. Encapsulation of alfentanil in the liposomes produced a significant decrease in the loss of corneal, paw step and righting reflex and a slight decrease in catalepsy and loss of the pinna response. There was no significant difference between liposome preparations in preventing side effects. L-multilamellar-DPPC produced allodynia in 100% of the animals whereas significantly less allodynia was observed with the other preparations. This study indicates that liposomal preparations can significantly enhance the therapeutic ratio of a lipid soluble opioid after spinal delivery. However, the choice of lipids for the formulation of liposomes intended for spinal drug delivery must be considered since the L-isomer and larger lipid load of multilamellar liposomes have a direct spinal effect leading to alledynia. Previous studies have in fact shown that spinal lysolecithin can yield focal demyelination.

Motor and blood pressure effects of epidural sustained-release bupivacaine from polymer microspheres: a dose-response study in rabbits

The incorporation of local anesthetics into injectable polymer microspheres can be useful in providing prolonged regional effects. This randomized study was designed to compare the effects of bupivacaine and bupivacaine-loaded microspheres on the time course of motor block in rabbits injected epidurally. Bupivacaine-loaded microspheres and drug-free microspheres 1-10 microns in size were devised from poly-d,l-lactic acid by using a solvent evaporation/extraction method. The effects of bupivacaine and of similar amounts of bupivacaine-loaded microspheres were studied in 26 rabbits as follows: 0.9% sodium chloride, followed by drug-free microspheres, then 1.25 mg of bupivacaine and 1.25 mg of bupivacaine-loaded microspheres (Group I; n = 8); 2.5 mg of bupivacaine, then 2.5 mg of bupivacaine-loaded microspheres (Group II; n = 8); and 5 mg of bupivacaine and 5 mg of bupivacaine-loaded microspheres (Group III; n = 10). Motor block was evaluated blindly by observation of walking disturbances, using a scale from 0 (free movements) to 3 (total limb paralysis). A period of 3 days elapsed between each injection. No limitation on movements was observed after 0.9% sodium chloride and drug-free microsphere injection. With 5 mg, both bupivacaine solutions provided complete motor block which was significantly more prolonged (+244% +/- 129%, mean +/- SD) with bupivacaine-loaded microspheres than bupivacaine. With 2.5 and 1.25 mg, block intensity was less marked, and block duration was shorter after administration of bupivacaine-loaded microspheres than after bupivacaine. We concluded that blocks resulting from bupivacaine-loaded microspheres are highly influenced by the amount of drug initially released by the polymer.