Liposphere local anesthetic timed-release for perineural site application

Freeze-drying of bupivacaine lipospheres: preparation, characterization, and evaluation of anti-microbial properties

PURPOSE

To prepare freeze-dried bupivacaine lipospheres intended for topical application in burn injuries. The aim was improving the storage stability and developing a prolonged release pattern to tackle the adverse reactions resulting from the frequent administration of bupivacaine.

METHODS

The lipospheres were prepared by hot-melt dispersion method employing bupivacaine base at 1.5 and 3%w/w, tristearin 6% w/w as the core while dipalmitoyl phosphatidylcholine (DPPC) and soy phosphatidylcholine (SPC) as the coat at 0.75, 1.5 and 3% w/w. The lotion was then freeze-dried and cryoprotected by sucrose 3% w/w. Evaluation was carried out through loading and release analysis, storage study, particle characterization including morphology, zeta potential and particle size as well as anti-microbial assessment.

RESULTS

The highest loading, (87.6 ± 0.1%), was achieved using bupivacaine 3% and SPC 0.75%. After 6 months of storage at 4 ͦC, the loading in the lotion and the freeze-dried samples were 17.4 ± 0.2 and 87.2 ± 0.3%, respectively. In vitro dissolution test demonstrated 94.5% and 95% of bupivacaine release from lotion and freeze-dried samples, after 24 h. The respective zeta potential of -1.30 and 26 mV was recorded for lotion and solid-state bupivacaine. Micromeritic evaluation of freeze-dried powder exhibited particle size of 35.23 ± 2.02 μm and highly-wrinkled-irregular morphology without detectable needle structures related to drug free crystals. The powder had rapid reconstitution property and antibacterial activity.

CONCLUSION

Freeze- drying holds a promising potential to improve the storage stability of bupivacaine lipospheres with well- preserved release pattern and particle properties for further topical application.

Brain Targeting of Quetiapine Fumarate via Intranasal Delivery of Loaded Lipospheres: Fabrication, In-Vitro Evaluation, Optimization, and In-Vivo Assessment

A liposphere system for intranasal delivery of quetiapine fumarate (QTF) was created to assess the potential for enhanced drug delivery. We investigated the effects of particle size, entrapment effectiveness, poly dispersibility index, and pluronic incorporation percentage on these variables. The optimal formula was examined using a TEM, and investigations into DSC, XRD, and FTIR were made. Optimized liposphere formulation in vitro dissolution investigation with a mean diameter of 294.4 ± 18.2 nm revealed about 80% drug release in 6 h. The intranasal injection of QTF-loaded lipospheres showed a shorter T_max compared to that of intranasal and oral suspension, per the findings of an in vivo tissue distribution investigation in Wistar mice. Lipospheres were able to achieve higher drug transport efficiency (DTE %) and direct nose-to-brain drug transfer (DTP %). A potentially effective method for delivering QTF to specific brain regions is the liposphere system.

Solid Lipid Microspheres Decorated Nanoparticles As Drug Carriers

While Pickering emulsions have been known since 1906, where oil droplets are dispersed in aqueous media owing to nanoparticles decorating each oil droplet, no solid lipid microparticles decorated with nanoparticles have been described. These Solid-Pickering microparticles are surfactant-free micro-scale spherical active agent carriers composed of beeswax as a natural solid lipid with chitosan and starch nanoparticles embedded in the surface. Microparticles of this type were made by dispersing molten lipid in hot aqueous media containing dispersed nanoparticles to create microdroplets. Once the droplets are cooled below the melting point of the lipid, the microparticles of spherical form are obtained. The novel system allows encapsulation of active agents within a solid lipid core which is slowly released over time. It has been demonstrated through encapsulation of Ibuprofen and Lidocaine as a model poorly water-soluble drugs and an extended-release profile (for at least a week) was achieved. These Solid Pickering microparticles can be used in food, medicine, agriculture, and personal care products.

An injectable mesoporous silica-based analgesic delivery system prolongs the duration of sciatic nerve block in mice with minimal toxicity

The major limitation of traditional local anesthetics is the finite duration of a single injection. The present study developed two kinds of novel injectable anesthetic nanocomposites based on mesoporous silica, and evaluated their long-lasting analgesic effect and biosafety. The nanoparticulate carriers, mesoporous silica nanoparticles (MSNs) and mesoporous silica-coated gold nanorods (GNR@MSN), were firstly constructed using the oil-water biphase reaction approach and then ropivacaine (RPC), a local anesthetic, was loaded into the mesoporous carriers by vacuum suction. Transmission electron microscopic images showed the well-ordered mesoporous structure for drug loading. RPC-loaded MSNs and RPC-loaded GNR@MSN exhibited a sustained-release pattern in vitro, and the latter also showed a controlled-release manner triggered by near-infrared (NIR) irradiation. RPC-loaded MSNs and RPC-loaded GNR@MSN caused an initial sensory blockade in mice that lasted for 6 h, almost 2.5 folds of that from free RPC solution. Furthermore, upon NIR irradiation, the latter induced three additional periods of the blockade. Neither of them showed motor nerve block, which may be due to the sustained release manner. The low myotoxicity and low neurotoxicity of the two nanocomposites were presented both in vitro and in vivo. These results demonstrate the potential of the mesoporous silica-based analgesic nanocomposites in effectively controlling postoperative pain, maybe RPC-loaded MSNs for moderate pain and RPC-loaded GNR@MSN for severe pain. STATEMENT OF SIGNIFICANCE: Adequate postoperative analgesia helps early functional exercise after surgery and accelerates rapid recovery, while uncontrolled postoperative pain probably develops chronic post-surgical pain that impacts the life quality of patients for a long time. However, postoperative pain management is still a challenge. The current treatment drugs are always accompanied by some side effects due to their systemic effect. Opioids have risks of addiction and respiratory depression, and nonsteroidal anti-inflammatory drugs can lead to gastrointestinal reaction. Therefore, the long-lasting local anesthetic formulation with good biocompatibility is the most promising solution to manage post-surgical pain. The present study developed novel injectable anesthetic nanocomposites based on mesoporous silica, providing long-lasting pain relief in mice with minimal toxicity.

Recent Developments in Solid Lipid Microparticles for Food Ingredients Delivery

Health food has become a prominent force in the market place, influencing many food industries to focus on numerous bioactive compounds to reap benefits from its properties. Use of these compounds in food matrices has several limitations. Most of the food bio-additives are sensitive compounds that may quickly decompose in both food and within the gastrointestinal tract. Since most of these bioactives are highly or partially lipophilic molecules, they possess very low water solubility and insufficient dispersibility, leading to poor bioavailability. Thus, various methods of microencapsulation of large number of food bioactives have been studied. For encapsulation of hydrophobic compounds several lipid carriers and lipid platforms have been studied, including emulsions, microemulsions, micelles, liposomes, and lipid nano- and microparticles. Solid lipid particles (SLP) are a promising delivery system, can both deliver bioactive compounds, reduce their degradation, and permit slow and sustained release. Solid lipid particles have important advantages compared to other polymer carriers in light of their simple production technology, including scale up ability, higher loading capacity, extremely high biocompatibility, and usually low cost. This delivery system provides improved stability, solubility in various matrixes, bioavailability, and targeting properties. This article reviews recent studies on microencapsulation of selected bioactive food ingredients in solid lipid-based carriers from a point of view of production methods, characteristics of obtained particles, loading capability, stability, and release profile.

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.

Tacrolimus and curcumin co-loaded liposphere gel: Synergistic combination towards management of psoriasis

Psoriasis is an autoimmune skin disorder characterized by hyper proliferation and poor differentiation of keratinocytes. It significantly affects patient's quality of life. This study reports the anti-psoriatic efficacy of tacrolimus and curcumin loaded liposphere gel formulation. Poor solubility, poor skin penetration and erratic absorption are some problems associated with the topical delivery of these drugs. To overcome these problems, lipospheres containing combination of tacrolimus and curcumin was prepared with a particle size of nearly 50nm and incorporated into a gel for topical application. Liposphere gel showed slow release of both the drugs and shear thinning behaviour that is desirable property of topical formulation. Further, dermal distribution study using dye loaded formulation suggested penetration of dye into skin layers. The therapeutic efficacy of tacrolimus and curcumin loaded liposphere gel was assessed on imiquimod induced psoriatic plaque model, and the level of expression of psoriatic biochemical markers was evaluated using enzyme-linked immunosorbent assay. Results indicated improvement in the phenotypic and histopathological features of psoriatic skin treated with tacrolimus and curcumin loaded liposphere gel. There was reduction in the level of TNF-α, IL-17 and IL-22 compared to imiquimod group. These results corroborate the premise that liposphere gel containing combination of tacrolimus and curcumin can be an effective strategy for the treatment of psoriasis.

Multivesicular liposomal bupivacaine at the sciatic nerve

Clinical translation of sustained release formulations for local anesthetics has been limited by adverse tissue reaction. Exparel™ (DepoFoam bupivacaine) is a new liposomal local anesthetic formulation whose biocompatibility near nerve tissue is not well characterized. Exparel™ injection caused sciatic nerve blockade in rats lasting 240 min compared to 120 min for 0.5% (w/v) bupivacaine HCl and 210 min for 1.31% (w/v) bupivacaine HCl (same bupivacaine content as Exparel™). On histologic sections four days after injection, median inflammation scores in the Exparel™ group (2.5 of 4) were slightly higher than in groups treated with bupivacaine solutions (score 2). Myotoxicity scores in the Exparel™ group (2.5 of 6) were similar to in the 0.5% (w/v) bupivacaine HCl group (3), but significantly less than in the 1.31% (w/v) bupivacaine HCl group (5). After two weeks, inflammation from Exparel™ (score 2 of 6) was greater than from 0.5% (w/v) bupivacaine HCl (1) and similar to that from 1.31% (w/v) bupivacaine HCl (1). Myotoxicity in all three groups was not statistically significantly different. No neurotoxicity was detected in any group. Tissue reaction to Exparel™ was similar to that of 0.5% (w/v) bupivacaine HCl. Surveillance for local tissue injury will be important during future clinical evaluation.

Analgesic and Micromeritic evaluations of SRMS-based oral Lipospheres of Diclofenac Potassium

The objective of our work was to study the micromeritic properties of lyophilized diclofenac potassium-loaded lipospheres and to evaluate in vivo, the analgesic properties of diclofenac potassium in the lipospheres in addition to other in vitro properties. Solidified reverse micellar solutions were prepared by fusion using 1:1, 2:1, and 1:2% w/w of Phospholipon(®) 90H and Softisan(®) 154. Diclofenac potassium (1, 3, and 5% w/w) was incorporated into the solidified reverse micellar solutions. Solidified reverse micellar solutions-based lipospheres were formulated by melt homogenization techniques using Ultra-Turrax homogenizer, and thereafter lyophilized to obtain water-free lipospheres. The lipospheres were characterized in terms of particle size and morphology, stability, thermal analysis, drug content, encapsulation efficiency, and loading capacity. The flow properties of the lipospheres were studied using both direct and indirect methods of assessing flow. The analgesic properties of the lipospheres were studied using the hot plate method. Results obtained showed that the yield of diclofenac potassium-loaded lipospheres was high and the particle size ranged from 0.61±0.07 to 2.55±0.04 μm. The lipospheres had high encapsulation efficiency of 95%, which was affected by the amount of drug loaded, while the loading capacity increased with the increase in drug loading. Diclofenac potassium-loaded lipospheres exhibited poor flow. The formulations exhibited good analgesic effect compared with the reference and had 84 to 86% drug release at 13 h. The lipospheres based on solidified reverse micellar solutions could be used for oral delivery of diclofenac potassium.

A novel ropivacaine-loaded in situ forming implant prolongs the effect of local analgesia in rats

INTRODUCTION

Prolonged postoperative analgesia cannot be achieved by a single injection of local anesthetic solution. The objective of this study was to optimize the formulation of a ropivacaine hydrochloride (Ropi-HCl) loaded in situ forming implant (ISI) by addition of different co-solvents, and evaluate the in vitro release of Ropi-HCl, and the analgesic effect and toxicity of the optimized formulation in rats.

MATERIAL AND METHODS

Triacetin (TA), benzyl benzoate (BB) and polyethylene glycol 400 (PEG 400) were used as additives and added to the solvent of N-methyl-2-pyrrolidone (NMP). Drug release to the surface and inner structural properties of the formed implant were evaluated by scanning electron microscopy (SEM). The analgesic effect was determined by injection near the rat sciatic nerve.

RESULTS

The solvent system added with TA or BB significantly decreased the burst release, whereas PEG 400 increased the Ropi-HCl burst release from the formulation. Over 70% of the incorporated Ropi-HCl was released from all formulations in 14 days in the in vitro assay. The SEM showed that the surface of NMP-BB formulation was less porous and more homogeneous, compared with the other formulations. Compared with Ropi-HCl injection, the optimized formulation (NMP-BB) significantly prolonged the analgesic effect in 48 h (p < 0.05), with a mild degree of motor block from 3 h to 12 h. Histological evaluation of the injection site revealed only mild inflammatory infiltration without obvious pathological nerve alterations.

CONCLUSIONS

The biodegradable Ropi-HCl-loaded ISI system with NMP-BB may prove to be an attractive and safe alternative for the delivery of parenteral local anesthetics to prolong pain relief.

Local toxicity from local anesthetic polymeric microparticles

BACKGROUND

Local tissue injury from sustained-release formulations for local anesthetics can be severe. There is considerable variability in reporting of that injury. We investigated the influence of the intrinsic myotoxicity of the encapsulated local anesthetic (lidocaine, low; bupivacaine, high) on tissue reaction in rats.

METHODS

Cytotoxicity from a range of lidocaine and bupivacaine concentrations was measured in C2C12 myotubes over 6 days. Rats were given sciatic nerve blocks with 4 microparticulate formulations of lidocaine and bupivacaine: 10% (w/w) lidocaine poly(lactic-co-glycolic) acid (PLGA), 10% (w/w) bupivacaine PLGA, 50% (w/w) lidocaine PLGA, and 50% (w/w) bupivacaine PLGA. Effectiveness of nerve blockade was assessed by a modified hotplate test and weightbearing measurements. Myotoxicity was scored in histologic sections of injection sites. Bupivacaine and lidocaine release kinetics from the particles were measured.

RESULTS

Median sensory blockade duration for 50% (w/w) lidocaine was 255 (90-540) minutes versus 840 (277-1215) minutes for 50% (w/w) bupivacaine (P = 0.056). All microparticulate formulations resulted in myotoxicity. The choice of local anesthetic did not influence the severity of myotoxicity. Median myotoxicity scores for 50% (w/w) lidocaine compared with 50% (w/w) bupivacaine at 4 days were 3.4 (2.1-4.2) vs 3.3 (2.9-3.5) (P = 0.44) and at 14 days 1.9 (1.8-2.4) vs 1.7 (1.3-1.9) (P = 0.23), respectively.

CONCLUSIONS

Lidocaine and bupivacaine PLGA microspheres resulted in similar degrees of myotoxicity, irrespective of drug loading. Intrinsic myotoxicity did not predict tissue injury from sustained release of these anesthetics. Caution is warranted in the use of such devices near muscle and nerve.

Thermoresponsive nanogels for prolonged duration local anesthesia

Nanogels based on poly(N-isopropylacrylamide) are attractive vehicles for prolonged duration local anesthesia because of their tunable size, number of functional groups, thermoresponsiveness and anionic charge. Nerve block durations of up to 9h were achieved using acrylic acid-loaded nanogels loaded with bupivacaine. Increasing the anionic charge density of the nanogels or (for more highly acid-functionalized nanogels) decreasing the nanogel size facilitated longer duration of anesthetic release. Small (<300 nm diameter) nanogels formed dense aggregates upon injection in vivo and induced only mild inflammatory responses, while large (>500 nm diameter) nanogels typically remained as liquid-like residues in vivo and induced more severe inflammatory reactions.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

The Safety of EXPAREL ® (Bupivacaine Liposome Injectable Suspension) Administered by Peripheral Nerve Block in Rabbits and Dogs

A sustained-release DepoFoam injection formulation of bupivacaine (EXPAREL, 15 mg/mL) is currently being investigated for postsurgical analgesia via peripheral nerve block (PNB). Single-dose toxicology studies of EXPAREL (9, 18, and 30 mg/kg), bupivacaine solution (Bsol, 9 mg/kg), and saline injected around the brachial plexus nerve bundle were performed in rabbits and dogs. The endpoints included clinical pathology, pharmacokinetics, and histopathology evaluation on Day 3 and Day 15 (2/sex/group/period). EXPAREL resulted in a nearly 4-fold lower C_max versus Bsol at the same dose. EXPAREL was well tolerated at doses up to 30 mg/kg. The only EXPAREL-related effect seen was minimal to mild granulomatous inflammation of adipose tissue around nerve roots (8 of 24 rabbits and 7 of 24 dogs) in the brachial plexus sites. The results indicate that EXPAREL was well tolerated in these models and did not produce nerve damage after PNB in rabbits and dogs.

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.

Intra-articular depot formulation principles: role in the management of postoperative pain and arthritic disorders

The joint cavity constitutes a discrete anatomical compartment that allows for local drug action after intra-articular injection. Drug delivery systems providing local prolonged drug action are warranted in the management of postoperative pain and not least arthritic disorders such as osteoarthritis. The present review surveys various themes related to the accomplishment of the correct timing of the events leading to optimal drug action in the joint space over a desired time period. This includes a brief account on (patho)physiological conditions and novel potential drug targets (and their location within the synovial space). Particular emphasis is paid to (i) the potential feasibility of various depot formulation principles for the intra-articular route of administration including their manufacture, drug release characteristics and in vivo fate, and (ii) how release, mass transfer and equilibrium processes may affect the intra-articular residence time and concentration of the active species at the ultimate receptor site.

Local myotoxicity from sustained release of bupivacaine from microparticles

BACKGROUND

Sustained release of local anesthetics is frequently associated with myotoxicity. The authors investigated the role of particulate delivery systems and of the pattern of drug release in causing myotoxicity.

METHODS

Rats were given sciatic nerve blocks with bupivacaine solutions, two types of bupivacaine-containing microparticles (polymeric microspheres and lipid-protein-sugar particles), or blank particles with or without bupivacaine in the carrier fluid. Myotoxicity was scored in histologic sections of the injection sites. Bupivacaine release kinetics from the particles were measured. Myotoxicity of a range of bupivacaine concentrations from exposures up to 3 weeks was assessed in C2C12 myotubes, with or without microparticles.

RESULTS

Both types of bupivacaine-loaded microparticles, but not blank particles, were associated with myotoxicity. Whereas 0.5% bupivacaine solution caused little myotoxicity, a concentration of bupivacaine that mimicked the amount of bupivacaine released initially from particles caused myotoxicity. Local anesthetics showed both concentration and time-dependent myotoxicity in C2C12s. Importantly, even very low concentrations that were nontoxic over brief exposures became highly toxic after days or weeks of exposure. The presence of particles did not increase bupivacaine myotoxicity in vitro but did in vivo. Findings applied to both particle types.

CONCLUSIONS

Whereas the release vehicles themselves were not myotoxic, both burst and extended release of bupivacaine were. A possible implication of the latter finding is that myotoxicity is an inevitable concomitant of sustained release of local anesthetics. Particles, and perhaps other vehicles, may enhance local toxicity through indirect mechanisms.

Lipospheres as carriers for topical delivery of aceclofenac: preparation, characterization and in vivo evaluation

The purpose of this study was to prepare lipospheres containing aceclofenac intended for topical skin delivery with the aim of exploiting the favorable properties of this carrier system and developing a sustained release formula to overcome the side effects resulting from aceclofenac oral administration. Lipospheres were prepared using different lipid cores and phospholipid coats adopting melt and solvent techniques. Characterization was carried out through photomicroscopy, scanning electron microscopy, particle size analysis, DSC, In vitro drug release and storage study. The anti-inflammatory effect of liposphere systems was assessed by the rat paw edema technique and compared to the marketed product. Results revealed that liposphere systems were able to entrap aceclofenac at very high levels (93.1%). The particle size of liposphere systems was well suited for topical drug delivery. DSC revealed the molecular dispersion of aceclofenac when incorporated in lipospheres. Both entrapment efficiency and release were affected by the technique of preparation, core and coat types, core to coat ratio and drug loading. Lipospheres were very stable after 3 months storage at 2-8 degrees C manifested by low leakage rate (less than 7%) and no major changes in particle size. Finally, liposphere systems were found to possess superior anti-inflammatory activity compared to the marketed product in both lotion and paste consistencies. Liposphere systems proved to be a promising topical system for the delivery of aceclofenac as they possessed the ability to entrap the drug at very high levels and high stability, and to sustain the anti-inflammatory effect of the drug.

An overview of lipid membrane supported by colloidal particles

In recent years, original hybrid assemblies composed of a particle core surrounded by a lipid shell emerged as promising entities for various biotechnological applications. Their broadened bio-potentialities, ranging from model membrane systems or biomolecule screening supports, to substance delivery reservoirs or therapeutic vectors, are furthered by their versatility of composition due to the possible wide variation in the particle nature and size, as well as in the lipid formulation. The synthesis, the characteristics, and the uses of these Lipid/Particle assemblies encountered in the literature so far are reviewed, and classified according to the spherical core size in order to highlight general trends. Moreover, several criteria are particularly discussed: i) the interactions involved between the particles and the lipids, and implicitly the assembly elaboration mechanism, ii) the most suited techniques for an accurate characterization of the entities from structural and physicochemical points of view, and iii) the remarkable properties of the solid-supported lipid membrane obtained.

Long acting local anesthetic–polymer formulation to prolong the effect of analgesia

Prolonged postoperative analgesia cannot be achieved using single injections of local anesthetic solutions. The study objective was to evaluate the efficacy and toxicity of a new formulation of bupivacaine loaded in an injectable fatty acid based biodegradable polymer poly(sebacic-co-ricinoleic acid) for producing motor and sensory block when injected near the sciatic nerve. Bupivacaine was dissolved in poly(fatty ester-anhydride) paste and tested for drug release in vitro and in vivo after injection in mice. The efficacy and toxicity of the polymer-drug combination was determined by injecting the polymer formulation near the sciatic nerve of mice and measure the sensory and motor nerve blockade for 48 h, while monitoring the animal general health and the injection site. Seventy percent of the incorporated drug was released during 1 week in vitro. Single injection of 10% bupivacaine in the polymer caused motor and sensory block that lasted 30 h. Microscopic examination of the injection sites revealed only mild infiltration in three of eight examined tissues with no pathological findings for internal organs were found. In conclusion the polymer poly(sebacic-co-ricinoleic acid) is a safe carrier for prolonged activity of bupivacaine.

The expulsion of lipophilic drugs from the cores of solid lipid microspheres in diluted suspensions and in concentrates

The aim of the study was to compare incorporation of bupivacaine base, bupivacaine stearate and indomethacin in diluted suspensions of lipospheres (10%, w/w of lipid) and in concentrates (50%, w/w of lipid). The lipid cores were composed of a mixture of solid and liquid triglycerides (Precirol and Miglyol 4:1). The lipospheres sizing between 0.5-10 microm (suspensions) and 0.5-20 microm (concentrates) were prepared using a hot emulsification with high-shear mixing and cold resolidification method. None of the studied drugs was successfully incorporated in the lipid core. The increased incorporation of drugs determined in the concentrated lipospheres was only apparent, since in fact all the dose was only attached to the surface of the lipid particles and was transferred to the aqueous phase in the course of an intensive agitation. The presence of hydrophilic polymers in the aqueous phase did not prevent the expulsion effect although drug precipitation was retarded. The expulsion effect did not correlate with the solubility of drugs determined in the bulk lipids.

Controlled, clinical trial assessing saphenous, tibial and common peroneal nerve blocks for the control of perioperative pain following femoro-tibial joint surgery in the nonchondrodystrophoid dog

OBJECTIVE

To determine whether bupivacaine peripheral nerve block of the saphenous, tibial and common peroneal nerves proximal to the femoro-tibial joint reduces peri-operative pain following extracapsular surgical stabilization of cranial cruciate ligament rupture in the nonchondrodystrophoid dog.

ANIMALS

Forty-one dogs with naturally acquired femoro-tibial joint instability. Study design Randomized, controlled, clinical trial.

METHODS

Dogs diagnosed with suspected cranial cruciate ligament injury based on physical and radiographic evidence were randomly assigned to treatment (bupivacaine) or control (saline) nerve blocks before femoro-tibial joint surgery. Pain scores, skin sensation, pain threshold to incisional pressure, time to first systemic 'rescue' opioid analgesic and total analgesic dose were evaluated for 24 hours. p < 0.05 was considered significant.

RESULTS

Treatment dogs had a significantly longer period of cutaneous desensitization than control dogs. There were no significant differences between treatment and control groups for pain score, pain threshold to incisional pressure, or time to first-rescue analgesic. The treatment group received significantly more supplemental analgesics than the control group.

CONCLUSIONS

These peripheral nerve blocks were easy to perform and resulted in significant desensitization of the associated nerve autonomous zones, but did not improve post-operative analgesia.

CLINICAL RELEVANCE

Clinical benefit was not detected when using this technique for peri-operative pain management following extracapsular cranial cruciate ligament surgical stabilization.

Solid lipid microparticles: formulation, preparation, characterisation, drug release and applications

This review details the properties of solid lipid microparticles (SLMs): a promising drug carrier system that has been until now rather unexploited. First, the advantages of SLMs compared with other drug carrier systems are listed. Then an overview of SLM manufacturing compounds and techniques is presented. A detailed discussion of the characteristics of SLMs follows, and includes the determination of particle size distribution, the determination of SLM morphology, the solid-state analysis, the determination of SLM drug loading and the factors influencing it. The in vitro drug release studies that have been carried out so far and the parameters affecting them are also described. Some preliminary in vivo aspects (in vivo drug release studies, biocompatibility studies and in vivo fate) are also considered.

Lipid-gel and poly(dimethylsiloxane) film to mimic bioaccumulation in adipocytes

Bioaccumulation is an increasingly important consideration in validation studies of the safety and efficacy of potential drugs. Although an "adipocyte" cell line model has been proven successful to mimic the accumulation of naphthalene in adipocytes, the prolonged incubation time limits its use in high-throughput studies and reduces reproducibility. In this investigation, naphthalene and naphthol accumulation and uptake kinetics of thin poly(dimethylsiloxane) (PDMS) film and lipid nanospheres suspended in a crosslinked gelatin gel (lipid-gel) were compared with those of adipocytes. Unlike the PDMS film, the lipid-gel can mimic the kinetics and extent of naphthalene accumulation in the adipocytes reasonably well. However, the lipid-gel accumulated about twice as much naphthol as the adipocytes, suggesting that hydrophobicity/hydrophilicity of the metabolite may be an important factor in the accuracy of accumulation studies with the lipid-gel. Nonetheless, the lipid-gel system shows promise as an inexpensive, convenient, and reproducible fat mimic for bioaccumulation studies.

Transdermal application of bupivacaine-loaded poly(acrylamide(A)-co-monomethyl itaconate) hydrogels

Bupivacaine, an amide local anaesthetic agent of long-acting and intense anaesthesia, was incorporated into poly(acrylamide(A)-co-monomethyl itaconate (MMI)) hydrogels. The swelling behaviour of two gel compositions, without drug, 75A/25MMI and 60A/40MMI, through rabbit ear skin, mounted on a modified Franz diffusion cell, was studied. Both gel compositions reach the equilibrium swelling degree (88.9+/-0.7 wt.% for 75A/25MMI and 92.5+/-0.1 wt.% for 60A/40MMI). The swelling kinetics was in accordance with the second Fick's Law; diffusion coefficients indicate faster swelling for gels with lower amount of monomethyl itaconic acid. The skin flux of bupivacaine solution through rabbit ear skin was 105+/-24 microg/cm(2)/h, the effective permeability coefficient was 26 x 10(-3)+/-9 x 10(-3)cm/h, and 77+/-15% of bupivacaine was permeated. Bupivacaine-loaded gels allow the drug was permeated through the skin. 47+/-4% and 36+/-3% of the drug amount included in 75A/25MMI and 60A/40MMI hydrogels, respectively, was permeated. The skin flux of the drug was between 90+/-5 and 16+/-7 microg/cm(2)/h depending on the amount of bupivacaine included in the gel and the gel composition. Skin flux increases with the drug load of the gels. Furthermore, as more MMI in the gel slower skin flux of the drug due to bupivacaine-gel interactions.

In-vitro release of bupivacaine from injectable lipid formulations investigated by a single drop technique--relation to duration of action in-vivo

The aim of this study was to develop an in-vitro release method suitable for injectable slow-release lipid formulations of local anaesthetics (or other drugs). We also aimed that the results of the in-vitro measurements should have a clear relationship to duration of action in-vivo. Six formulations of bupivacaine base in medium-chain triglyceride-glyceryl dilaurate mixtures were developed. A new apparatus was constructed for determination of their in-vitro release profiles. A bulbous glass tube was fixed inside a standard glass bottle, which was then filled with release medium. A stirring magnet was enclosed in the perforated polypropylene cylinder holding the glass tube. The stirring created a continuous, rotating downward flow of medium inside the tube, which kept the lipid phase, introduced by means of a syringe, suspended as a single, free drop. Release profiles were obtained by sampling of the release medium for up to 72 h and analysis by gas-liquid chromatography. The duration of action in-vivo of the respective formulations was tested by the hot-plate method in rats. The release profiles of bupivacaine in-vitro were mono-exponential for four formulations and bi-exponential for the other two. There was a positive correlation between the proportion of glyceryl dilaurate in the formulation and the slow half-life of release of bupivacaine. All formulations showed prolonged duration of action in-vivo, median values within the range 4.5-12 h, as compared with a 2-h effect of bupivacaine hydrochloride solution. A comparison of in-vitro release curves and durations of action in-vivo suggested that to maintain nerve blockade in-vivo the formulations must release bupivacaine at a rate of approximately 350 microg h(-1) under the in-vitro conditions. To conclude, we designed and tested a novel apparatus for measuring release of a local anaesthetic (or other drug) from a fluid or semi-solid formulation in-vitro. Release rates obtained in-vitro by means of this technique may be used to guide the development of formulations with suitable durations of action in-vivo. The apparatus is, however, as yet a prototype. Rigorous evaluation of performance should be carried out on devices built to specific standards according to their intended application.

Upper extremity nerve blocks

Anatomy favorable to the application of regional blockade, the capacity to decrease latency and prolong blockade, and the opportunity to facilitate recovery and decrease costs create a constellation of factors that have the potential to make upper extremity blockade a tremendously rewarding application of modern regional anesthetic technique. These rewards can be realized by the motivated anesthesiologist and shared with patients, surgical colleagues, and hospital administrators.

Local anesthetics for the pediatric patient

Local anesthetics are often extremely useful in the management of acute, chronic, and procedural pain. They have a low therapeutic ratio, so physicians should not exceed established dosing guidelines for a single bolus or long-term infusions. New local anesthetics that promise better safety and longer duration of action are on the horizon.