Cintia Maria Saia Cereda

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

PurposeLiposomal 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 evaluatein vivo drug-delivery systems, composed of large unilamellar liposomes (LUV), for bupivacaine (BVC) and mepivacaine (MVC).MethodsBVC and MVC hydrochloride were encapsulated into LUV (0.4 μm) composed of egg phosphatidylcholine, cholesterol and α-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.ResultsLiposomal formulations modified neither the intensity nor the duration of motor blockade compared to plain solutions. Concerning sensory blockade, liposomal BVC (BVCLUV) showed no advantage relatively to the plain BVC injection while liposomal MVC (MVCLUV) 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.ConclusionMVCLUV provided a LA effect comparable to that of BVC. We propose MVCLUV 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.RésuméObjectifDes préparations liposomales d’anesthésiques locaux (AL) peuvent contrôler l’administration de médicaments dans les systèmes biologiques, prolongeant leur effet anesthésique. Notre objectif était de préparer, caractériser et évaluer des systèmes d’administration de médicaments in vivo, composés de gros liposomes unilamellaires (GLU), pour la bupivacaïne (BVC) et la mépivacaïne (MVC).MéthodeLe chlorhydrate de BVC et de MVC a été mis en capsules dans des GLU (0,4 μm) composés de lécithine d’œuf, de cholestérol et de α-tocophérol (concentration molaire 4:3:0,07) pour obtenir des concentrations finales de 0,125, 0,25, 0,5 % pour la BVC et 0,5, 1, 2 % pour la MVC. La fonction motrice et les effets antinociceptifs ont été évalués par le blocage du nerf sciatique induit par des préparations liposomales et des préparations simples chez des souris.RésultatsLes préparations liposomales, comparées aux préparations simples, n’ont pas modifié l’intensité ni la duré du bloc moteur. Quant au bloc sensitif, la BVC liposomale (BVCLUV) n’a pas présenté d’avantage par rapport à l’injection de BVC simple tandis que la MVC liposomale (MVCLUV) a amélioré l’intensité (1,4–1,6 fois) et la duré du bloc sensitif (1,3–1,7 fois) comparée à la solution simple (P < 0,001). Ce qui laisse croire à une meilleure solubilité lipidique, à une disponibilité accrue et à une meilleure administration du médicament à libération contrôlée au site de l’injection.ConclusionLa MVCLUV fournit un effet AL comparable à celui de la BVC. Nous proposons l’administration de MVCLUV comme un nouveau choix possible de traitement de la douleur aiguë, puisque la préparation augmente la durée du bloc sensitif à des concentrations plus faibles que celles de la MVC simple.

Liposomal formulations of prilocaine, lidocaine and mepivacaine prolong analgesic duration

PurposeA laboratory investigation was undertaken to compare the in vivo antinociceptive effects of 2% liposomal formulations of prilocaine (PLC), lidocaine (LDC) and mepivacaine (MVC) compared to plain solutions of each of these three local anesthetics.MethodsLarge unilamellar vesicles were prepared by extrusion (400 nm), at pH 7.4. The membrane/water partition coefficients were obtained from encapsulation efficiency values, after incorporation of each local anesthetic to the vesicles. The anesthetic effect of each liposomal formulation was compared to the respective local anesthetic solution in water, using the infraorbital nerve-blockade test, in rats.ResultsThe partition coefficients were: 57 for PLC, 114 for LDC and 93 for MVC. In vivo results showed that local anesthetic-free liposomes, used as control, had no analgesic effect. In contrast, the encapsulated formulations induced increased intensities of total anesthetic effect (35.3%, 26.1 % and 57.1 %) and time for recovery (percentage increases of 30%, 23.1 % and 56%), respectively, for PLC, LDC and MVC when compared to the plain solutions (P < 0.01).ConclusionsThese results indicate that liposomes provide effective drug-delivery systems for intermediate-duration local anesthetics. Mepivacaine was affected to the greatest extent, while LDC benefited least from liposome encapsulation, possibly due to greater vasodilatory properties of LDC.ObjectifUne recherche en laboratoire a été entreprise pour comparer les effets antinociceptifs in vivo de préparations liposomiques de prilocaïne (PLC), de lidocaïne (LDC) et de mépivacaïne (MVC) à 2 %, à des solutions simples de chacun de ces anesthésiques locaux.MéthodeDe grandes vésicules unilamellaires ont été préparées par extrusion (400 nm), à un pH de 7,4. Les coefficients de partage membrane/eau ont été obtenus des valeurs d’efficacité de l’encapsulation, après l’introduction de chaque anesthésique local dans les vésicules. L’effet anesthésique de chaque préparation liposomique a été comparé à la solution respective d’anesthésique local dans l’eau par le test de blocage du nerf infra-orbitaire chez des rats.RésultatsLes coefficients de partage ont été de : 57 pour la PLC, 114 pour la LDC et 93 pour la MVC. Les résultats in vivo ont montré que les liposomes témoins sans anesthésique local n’avaient pas d’effet analgésique. Par contre, les préparations en capsules ont augmenté l’intensité anesthésique totale (35,3 %, 26,1 % et 57,1 %) et le temps de récupération (30 %, 23,1 % et 56 %) respectivement pour la PLC, la LDC et la MVC comparées aux solutions simples (P < 0,01).ConclusionCes résultats indiquent que les liposomes sont des systèmes de vecteurs de médicaments efficaces pour les anesthésiques locaux de durée moyenne. La MVC a surtout bénéficié, et la LDC le moins, de l’encapsulation liposomique, peut-être à cause de ses plus importantes propriétés vasodilatatrices.

Drug Delivery Systems for Local Anesthetics

Although technological innovations in the area of drug delivery claim for varied benefits, increasing the drug therapeutic index for human clinical application is the main goal pursued. Drug delivery systems for local anesthetics (LA) have attracted researchers due to many biomedical advantages associated to their application. Formulation approaches to systemically deliver LA include the encapsulation in liposomes, complexation in cyclodextrins, association with biopolymers and others carrier systems. Topical delivery systems for LA are characteristically composed by a diversity of adjuvants (viscosity inducing agents, preservatives, permeation enhancers, emollients,) and presentations such as semisolid (gel, creams, ointments), liquid (o/w and w/o emulsions, dispersions) and solid (patches) pharmaceutical forms. The proposed formulations aims to reduce the LA concentration used, increase its permeability and absorption, keep the LA at the target site for longer periods prolonging the anesthetic or analgesic effect and, finally, to decrease the clearance, local and systemic toxicity. This review deals with the innovations pertaining to formulations and techniques for drug-delivery of topical and injectable local anesthetics, as described in recent patents.

Micro and nanosystems for delivering local anesthetics

Introduction: One of the most common strategies for pain control during and after surgical procedures is the use of local anesthetics. Prolonged analgesia can be safely achieved with drug delivery systems suitably chosen for each local anesthetic agent. Areas covered: This review considers drug delivery formulations of local anesthetics designed to prolong the anesthetic effect and decrease toxicity. The topics comprise the main drug delivery carrier systems (liposomes, biopolymers, and cyclodextrins) for infiltrative administration of local anesthetics. A chronological review of the literature is presented, including details of formulations as well as the advantages and pitfalls of each carrier system. The review also highlights pharmacokinetic data on such formulations, and gives an overview of the clinical studies published so far concerning pain control in medicine and dentistry. Expert opinion: The design of novel drug delivery systems for local anesthetics must focus on how to achieve higher uploads of the anesthetic into the carrier, and how to sustain its release. This comprehensive review should be useful to provide the reader with the current state-of-art regarding drug delivery formulations for local anesthetics and their possible clinical applications.

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

We report here a novel observation that zolmitriptan induced CYP3A2 in male but not female rats. As part of our research programme to evaluate sex differences in the response to zolmitriptan, we studied the effects of zolmitriptan on CYP3A activity, protein and gene expression in male and female rats. Zolmitriptan was found to induce CYP3A activity, measured as testosterone and diazepam metabolism in-vitro, as well as midazolam pharmacokinetics in-vivo, in male but not female rats. The sex difference in response to zolmitriptan was further evaluated by analysis of CYP3A1/2 mRNA levels using real-time PCR, and CYP3A1/2 protein levels using immunoblotting. Zolmitriptan preferentially induced CYP3A2 in male but not female rats. No obvious effects on CYP3A1 were observed at any dose in either sex. Thus, we concluded that the observed sex-dependent induction of CYP3A by zolmitriptan was largely due to induction of CYP3A2 in male rats.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 alpha-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 (RVC(PLAIN)) and liposomal RVC (RVC(LUV)) 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 < 0.001) from liposomes. RVC(LUV) presented reduced cytotoxicity (P < 0.001) when compared with RVC(PLAIN). Treatment with RVC(LUV) increased the duration (P < 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 RVC(PLAIN). 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 RVC(PLAIN) or RVC(luv) at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVC(LUV) as a potential new formulation, since RVC is a new and safe local anaesthetic agent.

Local neurotoxicity and myotoxicity evaluation of cyclodextrin complexes of bupivacaine and ropivacaine.

BACKGROUND:Bupivacaine (BVC) and ropivacaine (RVC) are local anesthetics widely used in surgical procedures. In previous studies, inclusion complexes of BVC or RVC in hydroxypropyl-&bgr;-cyclodextrin (HP-&bgr;-CD) increased differential nervous blockade, compared to the plain anesthetic solutions. In this study we evaluated the local neural and muscular toxicity of these new formulations containing 0.5% BVC or RVC complexed with HP-&bgr;-CD (BVCHP-&bgr;-CD and RVCHP-&bgr;-CD). METHODS:Schwann cell viability was assessed by determination of mitochondrial dehydrogenase activity, and histopathological evaluation of the rat sciatic nerve was used to identify local neurotoxic effects (48 hours and 7 days after the treatments). Evaluations of serum creatine kinase levels and the histopathology of rat gastrocnemius muscle (48 hours after treatment) were also performed. RESULTS:Schwann cell toxicity evaluations revealed no significant differences between complexed and plain local anesthetic formulations. However, use of the complexed local anesthetics reduced serum creatine kinase levels 5.5-fold, relative to the plain formulations. The differences were significant at P < 0.05 (BVC) and P < 0.01 (RVC). The histopathological muscle evaluation showed that differences between groups treated with local anesthetics (BVC or RVC) and their respective complexed formulations (BVCHP-&bgr;-CD or RVCHP-&bgr;-CD) were significant (P < 0.05). CONCLUSIONS:We concluded that the new formulations presented a lower myotoxicity and a similar cytotoxic effect when compared to plain local anesthetic solutions.

Improvement of tetracaine antinociceptive effect by inclusion in cyclodextrins

Local anesthetics (LA) are among the most important pharmacological compounds used to attenuate or eliminate pain. However, systemic toxicity is still a limitation for LA application, especially for ester-type drugs, such as tetracaine (TTC) that presents poor chemical stability (due to hydrolysis by plasma esterases). Several approaches have been used to improve LA pharmaceutical properties, including the employment of drug-delivery systems. Here we used beta-cyclodextrin (β-CD) or hydroxypropyl-beta-cyclodextrin (HP-β-CD) to develop two new TTC formulations (TTC:β-CD and TTC:HP-β-CD). The inclusion complexes formation, in a 1:1 stoichiometry, was confirmed by differential scanning calorimetry, X-ray diffraction, UV-VIS absorption and fluorescence. Nuclear magnetic resonance (DOSY experiments) revealed that TTC association with HP-β-CD is stronger (Ka = 1200 mol/L−1) than with β-CD (Ka = 845 mol/L−1). Moreover, nuclear Overhauser effect (NOE) experiments provided information on the topology of the complexes, where TTC aromatic ring is buried inside the CD hydrophobic cavity. In vitro tests with 3T3 fibroblast cells culture revealed that complexation decreased TTC cytotoxicity. In addition, the total analgesic effect of TTC, tested in rats through the infraorbital nerve test, was improved in 36% with TTC:β-CD and TTC:HP-β-CD. In conclusion, these formulations presented potential for future clinical use, by reducing the toxicity and increasing the antinociceptive effect of tetracaine.

Bioadhesive films containing benzocaine: correlation between in vitro permeation and in vivo local anesthetic effect.

ABSTRACTPurposeThe aim of this work was to develop anesthetic bioadhesive films containing benzocaine and study their in vitro skin permeation and in vivo performance, in comparison with commercial formulations.MethodsFilms containing 3% and 5% w/w of benzocaine were prepared and characterized by weight, drug content, thickness and morphology. In vitro permeation assays were performed in vertical diffusion cells using full-thickness pig ear skin as barrier. Intensity and duration of analgesia were evaluated in rats by tail-flick test, and skin histological analysis was carried out.ResultsTail-flick test showed that the duration of benzocaine-induced analgesia was significantly prolonged with the films compared to commercial creams, in agreement with the higher in vitro permeation. Histological analysis of the rat tail skin did not reveal morphological tissue changes nor cell infiltration signs after application of the commercial creams or films.ConclusionsResults from our study indicate that the films developed in this work can be considered as innovative dermal/transdermal therapeutic systems for benzocaine local delivery.

Strategies for delivering local anesthetics to the skin: focus on liposomes, solid lipid nanoparticles, hydrogels and patches

Introduction: Dermal and transdermal drug delivery systems offer the possibility to control the release of the drug for an extended period of time. In particular, skin-delivery of local anesthetics (LA) is one of the most important strategies to increase the local drug concentration and to reduce systemic adverse reactions. Areas covered: During the development phase of new formulations for skin-delivery of LA one should consider a set of desirable features such providing suitable adhesion, easy application/removal and also to be biocompatible, biodegradable and non-toxic. This review emphasizes the main strategies for skin-delivery of LA considering those features in relation to the composition of the delivery systems described. The topics highlight the relationships between physico-chemical studies and pharmaceutical applications for liposomes and solid lipid nanoparticles as well as the formulation and clinical applications for hydrogels and patches. Expert opinion: The development of LA skin-delivery systems using hydrogels and different permeation enhancers, liposomes or lipid nanoparticles (as isolated carrier systems or as their dispersion in a gel-base) and patches have been explored as alternatives to commercial formulations, modifying the release rate of LA, increasing bioadhesive properties and reducing toxicity, resulting in an improved therapeutic efficacy. This review should provide to the reader a special emphasis on four delivery-systems, comprising the group of liposomes and lipid nanoparticles, hydrogels and patches technologies looking forward their application for skin anesthesia.

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

Abstract 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.