Liposomal formulations of prilocaine, lidocaine and mepivacaine prolong analgesic duration

Fresh Carrier for an Old Topical Local Anesthetic: Benzocaine in Nanostructured Lipid Carriers

Nanostructured lipid carriers (NLC) have emerged as innovative drug delivery systems, offering distinct advantages over other lipid-based carriers, such as liposomes and solid lipid nanoparticles. Benzocaine (BZC), the oldest topical local anesthetic in use, undergoes metabolism by pseudocholinesterase, leading to the formation of p-aminobenzoic acid, a causative agent for allergic reactions associated with prolonged BZC usage. In order to mitigate adverse effects and enhance bioavailability, BZC was encapsulated within NLC. Utilizing a 23 factorial design, formulations comprising cetyl palmitate (solid lipid), propylene glycol monocaprylate (liquid lipid), and Pluronic F68 as surfactants were systematically prepared, with variations in the solid/liquid lipid mass ratios (60:40-80:20%), total lipid contents (15-25%), and BZC concentrations (1-3%). The optimized formulation underwent characterization by dynamic light scattering, differential scanning calorimetry, Raman imaging, X-ray diffraction, small-angle neutron scattering, nanotracking analysis, and transmission electron microscopy (TEM)/cryo-TEM, providing insights into the nanoparticle structure and the incorporation of BZC into its lipid matrix. NLCBZC exhibited a noteworthy encapsulation efficiency (%EE = 96%) and a 1 year stability when stored at 25 °C. In vitro kinetic studies and in vivo antinociceptive tests conducted in mice revealed that NLCBZC effectively sustained drug release for over 20 h and prolonged the anesthetic effect of BZC for up to 18 h. We therefore propose the use of NLCBZC to diminish the effective anesthetic concentration of benzocaine (from 20 to 3% or less), thus minimizing allergic reactions that follow the topical administration of this anesthetic and, potentially, paving the way for new routes of BZC administration in pain management.

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

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

The Influence of Diabetic Peripheral Neuropathy on the Duration of Sciatic Nerve Block with 1.3% Liposomal Bupivacaine and 0.25% Bupivacaine Hydrochloride in a Mouse Model

Little is known regarding the pharmacological properties of extended-release local anesthetics in the setting of diabetic peripheral neuropathy. We investigated and compared the duration of sciatic nerve block following administration of clinically relevant concentrations of liposomal bupivacaine (LB) and bupivacaine hydrochloride (BH) in diabetic mice with peripheral neuropathy. In this prospective, randomized, and double-blind study, twenty-four female C57BL/6J-OlaHsd mice were assigned to a streptozotocin-induced type 1 diabetes group and a control group without diabetes. The presence of peripheral neuropathy was established by assessing the duration of thermal latency of the plantar and tail-flick tests, following which both groups were subdivided into two subgroups in which 35 mg/kg of 1.31% LB and 7 mg/kg of 0.25% BH were respectively administered for sciatic nerve block. The average sensory block duration with BH was 106 min and 117.1 min in the control and diabetic groups, respectively. With LB, the average sensory block duration was 118 min in the control mice, while in mice with diabetic peripheral neuropathy, the average block duration was significantly longer and above the 270 min limit set in our study. Accordingly, sensory block duration was longer with LB compared to BH, and diabetic peripheral neuropathy significantly increased sciatic nerve block duration with LB.

Improvement of Butamben Anesthetic Efficacy by the Development of Deformable Liposomes Bearing the Drug as Cyclodextrin Complex

This work was aimed at enhancing butamben (BTB) anesthetic efficacy by the "drug-in cyclodextrin (CD)-in deformable liposomes" strategy. In the study, phase-solubility studies with natural (α-, β-, γ-) and derivative (hydroxypropyl-α-and β-, sulfobutylether-β, methyl-β) CDs evidenced the highest BTB affinity for βCD and its derivatives and indicated methyl-βCD (RAMEB) as the best carrier. Drug-RAMEB complexes were prepared by different techniques and were characterized for solid-state and dissolution properties. The best BTB-RAMEB product was chosen for entrapment in the aqueous core of deformable liposomes containing stearylamine, either alone or with sodium cholate, as edge activators. Double-loaded (DL) liposomes, bearing the lipophilic drug (0.5% w/v) in the bilayer and its hydrophilic RAMEB complex (0.5% w/v) in the aqueous core, were compared to single-loaded (SL) liposomes bearing 1% w/v plain drug in the bilayer. All vesicles showed homogeneous dimensions (i.e., below 300 nm), high deformability, and excellent entrapment efficiency. DL-liposomes were more effective than SL ones in limiting drug leakage (<5% vs. >10% after a 3 months storage at 4 °C). In vivo experiments in rabbits proved that all liposomal formulations significantly (p < 0.05) increased the intensity and duration of drug anesthetic action compared to its hydroalcoholic solution; however, DL liposomes were significantly (p < 0.05) more effective than SL ones in prolonging BTB anesthetic effect, owing to the presence of the drug-RAMEB complex in the vesicle core, acting as a reservoir. DL liposomes containing both edge activators were found to have the best performance.

Safety and efficacy concerns of modern strategies of local anesthetics delivery

In the last few decades, several formulations have evolved to realize better efficacy of administered anesthesia. These innovative formulations have facilitated surgeons to perform operations under purely local anesthesia, which provides extra protection and comfort to patients. Ease of delivery of local anesthesia is the need of the current generation, because some of the standard procedures are performed without the use of any sedative agent. Therefore, we are presenting here the various approaches of administration of local anesthetics by the surgeons. To construct a comprehensive report on various methods of anesthesia, we followed a systematic literature search of bibliographic databases of published articles recently in the international journals and publishers of repute. A comprehensive study of several reports of the field indicates that there are significant progresses towards developing novel formulations of anesthesia drugs as well as strategies of delivery. Among formulations, nanoparticle-based delivery approaches, including polymeric, liposomal, and micellar structures, have offered the much needed efficacy with low toxicity. Therefore, several of such techniques are at various stages of clinical trials. Nanotechnology-based delivery approaches have significantly emerged in recent past due to the low systemic toxicity and better efficacy of the nonconventional local anesthetics. The other methods of local anesthesia delivery such as transdermal, magnetophoresis, electrophoresis, and iontophoresis are frequently used due to them being minimally invasive and locally effective. Therefore, the combination of the nanotechnological methods with above mentioned techniques would significantly enhance the overall process of local anesthesia delivery and efficacy.

Anaesthetic benefits of a ternary drug delivery system (Ropivacaine-in-Cyclodextrin-in-Liposomes): in-vitro and in-vivo evaluation

OBJECTIVES

To evaluate whether a ternary system composed of hydroxypropyl-β-cyclodextrin (HP-βCD) further encapsulated into egg phosphatidylcholine liposomes (LUV) could prolong the action and reduce the toxicity of ropivacaine (RVC).

METHODS

Dynamic light scattering and NMR were used to characterize the inclusion complex (RVC : HP-βCD), liposomal (RVC : LUV) and ternary (LUV : RVC : HP-βCD) systems containing 0.25% RVC. Their encapsulation efficiency, release kinetics, in-vitro cytotoxicity and in-vivo anaesthetic effect (paw-withdraw tests in mice) were also evaluated.

KEY FINDINGS

1 : 1 RVC : HP-βCD inclusion complex was encapsulated in liposomes (220.2 ± 20.3 nm size, polydispersity <0.25, zeta potentials = -31.7 ± 1.4 mV). NMR (diffusion-ordered spectroscopy (DOSY)) revealed stronger anaesthetic binding to LUV : RVC : HP-βCD (K_a  = 342 m^-1 ) than to RVC : HP-βCD (K_a  = 128 m^-1 ) or liposomal formulation (K_a  = 22 m^-1 ). The formulations promoted in-vitro sustained drug release and partially reverted the cytotoxicity of RVC against 3T3 fibroblasts in the profile: LUV : RVC : HP-βCD ≥ RVC : HP-βCD > RVC : LUV. Accordingly, in-vivo sensory block of free RVC (180 min) was prolonged ca. 1.7 times with the ternary system and RVC : HP-βCD (300 min) and 1.3 times with RVC : LUV (240 min).

CONCLUSIONS

These results confirm the suitability of this double-carrier system in clinical practice, to decrease the toxicity and prolong the anaesthesia time evoked by RVC.

Fusogenic Liposomes Increase the Antimicrobial Activity of Vancomycin Against Staphylococcus aureus Biofilm

Objective: The aim of the present study was to encapsulate vancomycin in different liposomal formulations and compare the in vitro antimicrobial activity against Staphylococcus aureus biofilms.

Methods: Large unilamellar vesicles of conventional (LUV VAN), fusogenic (LUV_fuso VAN), and cationic (LUV_cat VAN) liposomes encapsulating VAN were characterized in terms of size, polydispersity index, zeta potential, morphology, encapsulation efficiency (%EE) and in vitro release kinetics. The formulations were tested for their Minimum Inhibitory Concentration (MIC) and inhibitory activity on biofilm formation and viability, using methicillin-susceptible S. aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300 strains.

Key Findings: LUV VAN showed better %EE (32.5%) and sustained release than LUV_fuso VAN, LUV_cat VAN, and free VAN. The formulations were stable over 180 days at 4°C, except for LUV VAN, which was stable up to 120 days. The MIC values for liposomal formulations and free VAN ranged from 0.78 to 1.56 µg/ml against both tested strains, with no difference in the inhibition of biofilm formation as compared to free VAN. However, when treating mature biofilm, encapsulated LUV_fuso VAN increased the antimicrobial efficacy as compared to the other liposomal formulations and to free VAN, demonstrating a better ability to penetrate the biofilm.

Conclusion: Vancomycin encapsulated in fusogenic liposomes demonstrated enhanced antimicrobial activity against mature S. aureus biofilms.

Interfacial interaction of anesthetic lidocaine and mesoporous silica nanoparticles in aqueous solutions and its release properties

Lidocaine has been used as a local anesthetic by injection. The controlled release of lidocaine loaded into nanospheres is necessary to reduce the onset time of the anesthetic effect or increase the anesthetic analgesia duration. In this study, mesoporous silica nanoparticles (MSNs) with a large specific surface area were prepared by a sol-gel method, and the interfacial interaction between MSNs and lidocaine positively charged in aqueous solutions at different concentrations was investigated by adsorption tests, Fourier-transformed infrared spectroscopy, thermogravimetry-differential thermal analysis, and Brunauer-Emmett-Teller (BET) measurements. The electrostatic interaction between Si-OH on MSNs and lidocaine-NH⁺ was of importance for the adsorption phenomenon in aqueous solutions, indicating the monolayer adsorption of lidocaine. BET measurements also supported the decrease of pore volumes, and the hysteresis loop of the isotherm curve was not closed since the condensation of lidocaine in the mesopores formed micropores of less than 1.5 nm in size. The release profiles in phosphate buffered saline containing calcium and magnesium ions showed a rapid and higher release of lidocaine compared with that in phosphate buffered saline without divalent cations. The released lidocaine concentrations were sufficient for the expression of the anesthetic effect in dental anesthesia.

Poly (2-hydroxyethylmethacrylate -co-methylmethacrylate)/Lignocaine Contact Lens Preparation, Characterization, and in vitro Release Dynamic

2-hydroxyethyl methacrylate, methylmethacrylate, ethylene glycol dimethyl methacrylate, and lignocaine (drug) were mixed together and the monomers were copolymerized at 60 °C through a free radical polymerization in the presence of α,α'-Azoisobutyronitrile in tetrahydrofuran. A series of copolymer/drug composites with different monoacrylate monomer compositions were prepared by solvent evaporation and characterized by different methods such as nuclear magnetic resonance, differential scanning calorimetry, Fourier transform infrared, X-ray diffraction, and mechanical and optical testing. The water content in the copolymers and the cell viability test on the samples were also examined in this investigation. The results of the analyses of the properties of this drug-carrier system are promising, indicating that this material may be a potential candidate for contact lens applications. The release dynamic of this medication from the prepared drug-carrier systems was investigated in neutral pH media. The results obtained revealed that the diffusion of lignocaine through the copolymer matrix obeys the Fick model and the dynamic release can be easily controlled by the methyl methacrylate content in the copolymer.

Comparison of antinociceptive effects of plain lidocaine versus lidocaine complexed with hydroxypropyl-β-cyclodextrin in animal models of acute and persistent orofacial pain

Herein, it was investigated whether a complex of lidocaine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) would present a better antinociceptive profile in vivo when compared with plain lidocaine in models of orofacial pain. Plain lidocaine (LDC) and complexed lidocaine (LDC:HP-β-CD) were initially evaluated in vitro to determine the release rate of the two formulations. Subsequently, the effect of both formulations was evaluated in independent groups of rats submitted to the orofacial formalin test, induction of facial heat hyperalgesia by capsaicin and carrageenan, and induction of facial heat and mechanical hyperalgesia by constriction of the infraorbital nerve. LDC:HP-β-CD led to a reduction in the lidocaine release assessed in the in vitro release assay compared to plain LDC. Both formulations presented an antinociceptive effect in all models, but LDC:HP-β-CD showed a better effect in the second phase of the formalin response, in carrageenan-induced heat hyperalgesia, and in the heat hyperalgesia associated to infraorbital nerve constriction. Our results show that complexation improved in vivo antinociceptive effects of LDC, but further studies are necessary to elucidate what properties contribute to the better effect of the complexed formulation on this models and/or what characteristics of the pain model facilitate the action of the complexed formulation.

Liposomal-based lidocaine formulation for the improvement of infiltrative buccal anaesthesia

This study describes the encapsulation of the local anaesthetic lidocaine (LDC) in large unilamellar liposomes (LUV) prepared in a scalable procedure, with hydrogenated soybean phosphatidylcholine, cholesterol and mannitol. Structural properties of the liposomes were assessed by dynamic light scattering, nanoparticle tracking analysis and transmission electron microscopy. A modified, two-compartment Franz-cell system was used to evaluate the release kinetics of LDC from the liposomes. The in vivo anaesthetic effect of liposomal LDC 2% (LUV_LDC) was compared to LDC 2% solution without (LDC_PLAIN) or with the vasoconstrictor epinephrine (1:100 000) (LDC_VASO), in rat infraorbital nerve blockade model. The structural characterization revealed liposomes with spherical shape, average size distribution of 250 nm and low polydispersity even after LDC incorporation. Zeta potential laid around -30 mV and the number of suspended liposomal particles was in the range of 10¹² vesicles/mL. Also the addition of cryoprotectant (mannitol) did not provoke structural changes in liposomes properties. In vitro release profile of LDC from LUV fits well with a biexponential model, in which the LDC encapsulated (EE% = 24%) was responsible for an increase of 67% in the release time in relation to LDC_PLAIN (p < 0.05). Also, the liposomal formulation prolonged the sensorial nervous blockade duration (∼70 min), in comparison with LDC_PLAIN (45 min), but less than LDC_VASO (130 min). In this context, this study showed that the liposomal formulations prepared by scalable procedure were suitable to promote longer and safer buccal anaesthesia, avoiding side effects of the use of vasoconstrictors.

Current progress and challenges of nanoparticle-based therapeutics in pain management

Pain is a widespread and growing health problem worldwide that exerts a considerable social and economic impact on both patients and healthcare systems and, therefore, on society in general. Although current treatment modalities include a wide variety of pharmacological and non-pharmacological approaches, due to the complexity of pain and individual differences in clinical response these options are not always effective in mitigating and relieving pain. In addition, some pain drugs such as non-steroidal anti-inflammatory drugs (NSAIDs), local anesthetics and opioids show several unfavorable side effects. Therefore, current research advances in this medical field are based on the development of potential treatments to address many of the unmet needs and to overcome the existing limitations in pain management. Nanoparticle drug delivery systems present an exciting opportunity as alternative platforms to improve efficacy and safety of medications currently in use. Herein, we review a broad range of nanoparticle formulations (organic nanostructures and inorganic nanoparticles), which have been developed to encapsulate an array of painkillers, paying special attention to the key advantages that these systems offer, (compared to the use of the free drug), as well as to the more relevant results of preclinical studies in animal models. Additionally, we will briefly discuss the impact of some of these nanoformulations in clinical trials.

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.

Pharmacokinetic study of liposome-encapsulated and plain mepivacaine formulations injected intra-orally in volunteers

Objectives

The pharmacokinetics of commercial and liposome-encapsulated mepivacaine (MVC) injected intra-orally in healthy volunteers was studied.

Methods

In this double blind, randomized cross-over study, 15 volunteers received, at four different sessions, 1.8 ml of the following formulations: 2% MVC with 1 : 100 000 epinephrine (MVC2%EPI), 3% MVC (MVC3%), 2% and 3% liposome-encapsulated MVC (MVC2%LUV and MVC3%LUV). Blood samples were collected pre dose (0 min) and at 15, 30, 45, 60, 90, 120, 180, 240, 300, 360 min after injections. Liquid chromatography-tandem mass spectrometry was used to quantify plasma MVC concentrations.

Results

Pharmacokinetic analysis showed that the maximum plasma concentration (Cmax) and the areas under the curves (AUC0–360 and AUC0–∞) after MVC2%LUV and MVC2%EPI injections were smaller (P &lt; 0.05) than the equivalent figures for MVC3% and MVC3%LUV. The time to maximum plasma concentration (Tmax) and the half-life of elimination (t½beta) obtained after the treatment with MVC2%LUV, MVC2%EPI, MVC3% and MVC3%LUV presented no statistically significant differences (P &gt; 0.05). Cmax, AUC0–360 and AUC0-∞ after injection of the 2% formulations (MVC2%LUV and MVC2%EPI) did not exhibit statistically significant differences (P &gt; 0.05). The pharmacokinetics of MVC2%LUV were comparable to the pharmacokinetics of MVC2%EPI.

Conclusion

The liposomal formulation of 2% MVC exhibits similar systemic absorption to the local anesthetic with vasoconstrictor.

Prilocaine-cyclodextrin-liposome: effect of pH variations on the encapsulation and topology of a ternary complex using 1H NMR

A better comprehension of the prilocaine (PLC)-β-cyclodextrin (β-CD) complex liberation to membranes was provided by studying the architectural supramolecular arrangements of PLC, β-CD and egg phosphatidylcholine (EPC) liposomes, a membrane model. The topologies and possible interactions of mixtures of PLC, β-CD and EPC liposomes were investigated by nuclear magnetic resonances combining experimental (1)H-NMR (1D ROESY, STD and DOSY) at different pHs. The results indicate that in the mixture PLC/β-CD/EPC at pH 10 the PLC molecules are almost totally embedded into the liposomes and little interaction was observed between PLC and β-CD. However, at pH 5.5 not only was PLC imbedded in the EPC bilayer, but PLC was also interacting with β-CD. These results were rationalized as a spontaneous PLC release from β-CD to liposomes vesicles, whereas the PLC/EPC complex formation was higher at pH 10 than pH 5.5.

Coarse grained simulations of local anesthetics encapsulated into a liposome

We investigated the encapsulation of prilocaine (PLC), an aminoamide local anesthetic widely used in dentistry, into a small unilamellar liposome. We extended a recently developed coarse grained model to access the problem relevant time and length scales. Molecular dynamics (MD) simulations for different protonation states of the PLC captured important features of the PLC-vesicle interactions. We found that all neutral PLC molecules (nPLC) rapidly diffuse into the hydrophobic region of the vesicle adopting an asymmetric bimodal density distribution, with nPLC molecules jumping between the internal and external vesicle monolayers. Protonated PLC molecules (pPLC) initially placed in water were instead only found on the external monolayer, with a high rate of exchange with the water phase and no access to the inner part of the liposome. Although electrostatic interaction between pPLC tails and oppositely charged lipid head groups is shown to be structured, hydrophobicity is the driving force of PLC drug absorption within the liposome. Our simulations also show that a major percentage of pPLC remains trapped within the interior water phase of the liposome when starting from a configuration with pPLC distributed within the lipid membrane. This suggests that at low pH liposome-PLC complexes and therefore drug efficacy can strongly depend on the preparation procedure.

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.

Liposomal formulations of prilocaine: effect of complexation with hydroxypropyl-ß-cyclodextrin on drug anesthetic efficacy

A combined strategy, based on cyclodextrin complexation and loading in liposomes, has been investigated to develop a new delivery system with improved therapeutic activity of the local anesthetic, prilocaine (PRL). In order to evaluate the actual effectiveness and advantages of this approach compared to the traditional drug-in-liposome one, four different liposomal formulations were prepared: (1) liposomes loaded with PRL base as complex with hydroxypropyl-β-cyclodextrin (HP CD) in the aqueous phase; (2) liposomes loaded with PRL hydrochloride in the aqueous phase; (3) liposomes loaded with PRL base in the lipophilic phase; and (4) "double-loaded" liposomes, containing free PRL base in the membrane bilayer and its HP CD complex in the aqueous compartment. All batches were characterized for particle size, charge, deformability, and entrapment efficiency from using, respectively, light scattering, extrusion, and dialysis techniques, while the anesthetic effect was evaluated in vivo on Guinea pigs, according to the test of dorsal muscle contraction. All drug liposomal dispersions showed enhanced analgesic duration with respect to the corresponding aqueous solutions, but significant differences were observed between the different formulations. In particular, cyclodextrin complexation not only allowed an efficient encapsulation of PRL base in the aqueous vesicle core, but also increased the anesthetic effect duration and reduced the initial lag time, in comparison with the corresponding formulations containing, respectively, free PRL in the lipophilic phase or PRL hydrochloride in the aqueous vesicle core. The technique of double loading was the most effective, giving rise to the shortest onset time and longest duration of anesthetic effect.

Long-lasting infiltration anaesthesia by lidocaine-loaded biodegradable nanoparticles in hydrogel in rats

BACKGROUND

Infiltration of a long-lasting anaesthetic is helpful during the post-operative period. The recently developed local drug delivery system, biodegradable nanoparticles in a thermo-sensitive hydrogel (nanogel system), may possibly provide an extended duration of drugs. Therefore, we evaluated whether prolonged infiltration anaesthesia could be achieved by loading lidocaine into this delivery system.

METHODS

Thirty male rats were randomized into five groups of six rats each: saline; 2% hydrochloride lidocaine solution; lidocaine-loaded nanogel system and its compositing formulations, namely lido-nano gel; lido-nano; and lidogel. Durations of local anaesthesia with subcutaneously injected agents were measured by tail flick latency tests in a randomized, blind fashion.

RESULTS

Lido-nano gel produced effective anaesthesia for 360+/-113 min, compared with 150+/-33 min by lidogel, 180+/-37 min by lido-nano, and 110+/-45 min by lidocaine solution (P<0.001, means+/-SD), and elicited complete sensory blockade for 300+/-114 min, compared with 75+/-37 min by lidogel, 105+/-53 min by lido-nano, and 60+/-33 min by lidocaine solution (P<0.001, means+/-SD) without severe skin/systemic toxicity.

CONCLUSION

Lidocaine-loaded biodegradable nanoparticles in hydrogel produced prolonged infiltration anaesthesia in rats without severe toxicity, indicating a possible way to develop long-lasting local anaesthetics.

Update on the role of paravertebral blocks for thoracic surgery: are they worth it?

PURPOSE OF REVIEW

To consider optimal analgesic strategies for thoracic surgical patients.

RECENT FINDINGS

Recent studies have consistently suggested analgesic equivalence between paravertebral and thoracic epidural analgesia. Complications appear to be significantly less common with paravertebral analgesia.

SUMMARY

There is good evidence that paravertebral block can provide acceptable pain relief compared with thoracic epidural analgesia for thoracotomy. Important side-effects such as hypotension, urinary retention, nausea, and vomiting appear to be less frequent with paravertebral block than with thoracic epidural analgesia. Paravertebral block is associated with better pulmonary function and fewer pulmonary complications than thoracic epidural analgesia. Importantly, contraindications to thoracic epidural analgesia do not preclude paravertebral block, which can also be safely performed in anesthetized patients without an apparent increased risk of neurological injury. The place of paravertebral block in video-assisted thoracoscopic surgery is less clear.

Prolonged duration local anesthesia with minimal toxicity

Injectable local anesthetics that would last for many days could have a marked impact on periprocedural care and pain management. Formulations have often been limited in duration of action, or by systemic toxicity, local tissue toxicity from local anesthetics, and inflammation. To address those issues, we developed liposomal formulations of saxitoxin (STX), a compound with ultrapotent local anesthetic properties but little or no cytotoxicity. In vitro, the release of bupivacaine and STX from liposomes depended on the lipid composition and on whether dexamethasone was incorporated. In cell culture, bupivacaine, but not STX, was myotoxic (to C2C12 cells) and neurotoxic (to PC12 cells) in a concentration- and time-dependent manner. Liposomal formulations containing combinations of the above compounds produced sciatic nerve blockade lasting up to 7.5 days (with STX + dexamethasone liposomes) in male Sprague-Dawley rats. Systemic toxicity only occurred where high loadings of dexamethasone increased the release of liposomal STX. Mild myotoxicity was only seen in formulations containing bupivacaine. There was no nerve injury on Epon-embedded sections, and these liposomes did not up-regulate the expression of 4 genes associated with nerve injury in the dorsal root ganglia. These results suggest that controlled release of STX and similar compounds can provide very prolonged nerve blocks with minimal systemic and local toxicity.

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.

Non-opioid strategies for acute pain management

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