Local anesthetics: interaction with human erythrocyte membranes as studied by ¹H and 31P nuclear magnetic resonance

The literature carries many theories about the mechanism of action of local anesthetics (LA). We can highlight those focusing the direct effect of LA on the sodium channel protein and the ones that consider the interaction of anesthetic molecules with the lipid membrane phase. The interaction between local anesthetics and human erythrocyte membranes has been studied by ¹H and 31P nuclear magnetic resonance spectroscopy. It was found that lidocaine (LDC) and benzocaine (BZC) bind to the membranes, increase the mobility of the protons of the phospholipid's acyl chains, and decrease the mobility and/or change the structure of the polar head groups. The results indicate that lidocaine molecules are inserted across the polar and liquid interface of the membrane, establishing both electrostatic (charged form) and hydrophobic (neutral form) interactions. Benzocaine locates itself a little deeper in the bilayer, between the interfacial glycerol region and the hydrophobic core. These changes in mobility or conformation of membrane lipids could affect the Na+-channel protein insertion in the bilayer, stabilizing it in the inactivated state, thus causing anesthesia.6671Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effects of Gabaergic phenols on phospholipid bilayers as evaluated by 1H-NMR

The phenols propofol and thymol, and lately carvacrol, eugenol and chlorothymol, have been shown to act as positive allosteric modulators on GABAA receptor, which is the main inhibitory receptor of the central nervous system. GABAA receptor is an intrinsic membrane protein which activity may be affected by surface-active compounds and by physical changes in the membrane. Recently, we demonstrated that these phenols interacted with the lipid membrane phase, suggesting their anesthetic activity could be the combined result of their specific (with receptor proteins) as well as nonspecific (with surrounding lipid molecules) interaction modulating the supramolecular organization of the receptor environment. In the current study, by using 1H-NMR spectroscopy, we have investigated the effects of the insertion and the possible preferential location of the five phenol derivatives with GABAergic activity on EPC membranes. The results indicate that all compounds are able to insert in EPC phospholipid vesicles and to locate in the region between the polar group (choline molecule), the glycerol and the first atoms of the acyl chains, being the more lipophilic compounds (propofol and chlorothymol) that seem to prefer a deeper bilayer insertion. The location of the phenol molecules would reduce the repulsive forces among phospholipids head groups allowing closer molecular packing and finally diminishing the mobility of the hydrocarbon chains, as revealed by 1H spin relaxation times.Fil: Reiner, Gabriela de Las Nieves. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidade Estadual de Campinas; Brasil. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Fraceto, Leonardo Fernandes. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Paula, Eneida de. Universidade Estadual de Campinas; BrasilFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Garcia, Daniel Asmed. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

Validation of analytical methodology by HPLC for quantification of bupivacaine (S75-R25) in poli-lactide-co-glicolide nanospheres

Bupivacaine (S75-R25, NovaBupi®) is an amide type local anesthetic widely used. The present work consists of the development and validation of analytical methodology for evaluation of NovaBupi® content in the poly-lactide-co-glycolide nanospheres (PLGA-NS) by high performance liquid chromatography. The separation was made using the reversed-phase column LC-18, acetonitrile/phosphate buffer 85:15 v/v as mobile phase and detection at 220 nm. The results obtained show that the analytical methodology is accurate, reproducible, robust and linear over the concentration range 10-220.0 g/mL of NovaBupi®. The method was applied to determine the encapsulation efficiency and evaluate the release profile of NovaBupi®, showing good results.21522155Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Validação de metodologia analítica por cromatografia líquida de alta eficiência para quantificação de bupivacaína (S75-R25) em nanoesferas de poli(lactídeo-co-glicolídeo)

Bupivacaine (S75-R25, NovaBupi®) is an amide type local anesthetic widely used. The present work consists of the development and validation of analytical methodology for evaluation of NovaBupi® content in the poly-lactide-co-glycolide nanospheres (PLGA-NS) by high performance liquid chromatography. The separation was made using the reversed-phase column LC-18, acetonitrile/phosphate buffer 85:15 v/v as mobile phase and detection at 220 nm. The results obtained show that the analytical methodology is accurate, reproducible, robust and linear over the concentration range 10-220.0 g/mL of NovaBupi®. The method was applied to determine the encapsulation efficiency and evaluate the release profile of NovaBupi®, showing good results

Preparation of the orgamomodified cellulose acetate membranes for adsorption of the ions Cu(II), Cd(II), Mn(II) AND Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed

Pharmacokinetic profile of liposome-encapsulated ropivacaine after maxillary infiltration anaesthesia

The aim of this study was to determine the pharmacokinetic parameters of liposomal ropivacaine after dental anesthesia in 14 healthy volunteers. In this randomized, double-blind and crossover study, the volunteers received maxillary infiltration of liposome-encapsulated 0.5% ropivacaine and, 0.5% ropivacaine with 1:200,000 epinephrine in two different sessions. Blood samples were collected before and after (from 15 to 1440 min) the administration of either ropivacaine formulation. HPLC with UV detection was used to quantify plasma ropivacaine concentrations. The pharmacokinetic parameters AUC(0-24) (area under the plasma concentration x time curve from baseline to 24 h), AUC(0-infinity) (area under the plasma concentration-time curve from baseline to infinity), C-max (maximum drug concentration), CL (renal clearance), T-max (maximum drug concentration time), t(1/2) (elimination half-life) and Vd (volume of distribution) were analyzed using the Wilcoxon signed-rank test. No differences (p > 0.05) were observed between both formulations for any of the pharmacokinetic parameters evaluated and plasma ropivacaine concentrations, considering each period of time. Both formulations showed similar pharmacokinetic profiles, indicating that the liposomal formulation could be a safer option for use of this local anesthetic, due to the absence of a vasoconstrictor

Drug-delivery systems for racemic bupivacaine (S50-R50) and bupivacaine enantiomeric mixture (S75-R25): cyclodextrins complexation effects on sciatic nerve blockade in mice

BACKGROUND AND OBJECTIVES: Bupivacaine-induced side effects have led to the search for new local anesthetics (LA) with similar potency and lower toxicity, such as bupivacaine enantiomeric mixture (S75-R25). Drug-delivery systems for LA in carriers, such as cyclodextrins (CD), have been developed to improve anesthetic potency and therapeutic index of those drugs. This study aimed at preparing, characterizing and evaluating the anesthetic efficacy of inclusion complexes of bupivacaine enantiomeric mixture (S75-R25) and racemic bupivacaine (S50-R50) with hydroxypropylb- cyclodextrin (HPb-CD) comparing them to clinically available preparations. METHODS: Inclusion complexes were obtained by mixing appropriate volumes of HPb-CD and S50-R50 or S75-R25 to final 1:1 or 1:2 molar ratios and were characterized by phase solubility experiments. Affinity constants (K) were determined between HPb-CD and each LA. Motor and sensory blocks induced by plain or complexed LA formulations were evaluated in mice by sciatic nerve block. Three LA concentrations were used during the experiment: 0.125, 0.25 and 0.5%. RESULTS: Solubility experiments results were indicative of S50-R50:HPb-CD and S75-R25:HPb-CD complexation, with similar affinity constant (K) values: 14.7 M-1 and 14,3 M-1, respectively. In vivo experiments have shown that complexation has enhanced differential nerve blockade induced by LA: i) motor blockade duration induced by S75-R25 was similar, to the induced by but less intense S50-R50 ( p < 0.001). S50-R50HPb-CD and S75-R25HPb-CD complexes have decreased onset (p < 0.01 and p < 0.05, respectively), without changing motor block intensity (Emax) as compared to plain drugs; ii) sensory block evaluation has revealed higher analgesic intensity with S50-R50HPb-CD (2-fold, p < 0.001) and S75-R25HPb-CD (1.5-1.8-fold, p < 0.01 and p < 0.001, respectively) with both molar ratios (1:1 and 1:2, LA:CD), in addition to prolonging analgesic effect as compared to S50-R50 and S75-R25. CONCLUSIONS: More pronounced analgesic effects obtained by complexation with HPb-CD have shown that both formulations, S50-R50HPb-CD and S75-R25HPb-CD, are very useful for postoperative pain relief, requiring lower LA concentrations. Nevertheless, it is worth noticing that S75-R25 - being less toxic than racemic bupivacaine - is an interesting alternative for the development of more effective and safe drug-delivery systems as compared to racemic bupivacaine (S50-R50).JUSTIFICATIVA E OBJETIVOS: Os efeitos adversos associados ao uso de bupivacaína levaram à procura por novos anestésicos locais (AL) com perfil de bloqueio semelhante e menos tóxicos, surgindo novas preparações como a mistura enantiomérica de bupivacaína (S75-R25). Os sistemas de liberação controlada, contendo AL em carreadores como ciclodextrinas (CD), têm como objetivo melhorar a eficácia anestésica e o índice terapêutico dessas drogas. Este estudo visou a preparação, a caracterização e a avaliação da eficácia anestésica dos complexos de inclusão da mistura enantiomérica da bupivacaína (S75-R25) e da bupivacaína racêmica (S50-R50) com hidroxipropilb-ciclodextrina (HPb-CD) comparando-os com as preparações atualmente utilizadas na clínica. MÉTODO: Os complexos de inclusão foram preparados misturando-se quantidades apropriadas de HPb-CD e S50-R50 ou S75-R25 nas razões molares (1:1 e 1:2) e caracterizados por estudos de solubilidade de fases. Determinaram-se as constantes de afinidade (K) de cada AL pela HPb-CD. Os bloqueios motor e sensorial induzidos pelas drogas livres e complexadas foram avaliados, em camundongos, através do bloqueio do nervo ciático. Para a realização dos experimentos, utilizaram-se três concentrações de AL: 0,125%; 0,25% e 0,5%. RESULTADOS: Os estudos de solubilidade indicaram a formação de complexos de inclusão de S50-R50 e S75-R25 com HPb-CD, com valores de constante de afinidade (K) similares para os dois anestésicos: 14,7 M-1 (S50-R50:HP-bCD) e 14,3 M-1 (S75-R25:HP-bCD). Os testes em animais mostraram que a complexação potencializou o bloqueio nervoso diferencial induzido pelos AL: i) a duração do bloqueio motor induzido por S75-R25 foi similar à do S50-R50, mas menos intenso (p < 0,001). Já os complexos, S50-R50HPb-CD e S75-R25HPb-CD reduziram a latência (p < 0,01 e p < 0,05, respectivamente) sem modificar a intensidade do bloqueio motor (Emáx), em relação às drogas livres; ii) a avaliação do bloqueio sensorial mostrou aumento na intensidade da analgesia com os sistemas S50-R50HPb-CD (2 vezes, p < 0,001) e S75-R25HPb-CD (1,5-1,8 vezes; p < 0,01 e p < 0,001, respectivamente), nas duas proporções molares (1:1 e 1:2, AL:CD), além do prolongamento da duração do efeito analgésico, quando comparados às formulações S50-R50 e S75-R25. CONCLUSÕES: Os efeitos analgésicos mais pronunciados, obtidos após a complexação com HPb-CD, mostram que ambas as formulações, S50-R50HPb-CD e S75-R25HPb-CD, são de grande interesse para o alívio da dor no período pós-operatório, com a vantagem de serem administradas em menores concentrações. Entretanto, há que se ressaltar que a mistura enantiomérica de bupivacaína (S75-R25), por ser menos tóxica, representa uma alternativa no desenvolvimento de formulações de liberação controlada mais seguras e eficazes do que com a bupivacaína racêmica (S50-R50).JUSTIFICATIVA Y OBJETIVOS: Los efectos adversos asociados al uso de bupivacaína llevaron a la búsqueda por nuevos anestésicos locales (AL) con perfil de bloqueo semejante y menos tóxicos, surgiendo nuevas preparaciones como la mezcla enantiomérica de bupivacaína (S75-R25). Los sistemas de liberación controlada, conteniendo AL en carreadores como ciclodextrinas (CD), tienen como objetivo mejorar la eficacia anestésica y el índice terapéutico de esas drogas. Este estudio visó la preparación, caracterización y evaluación de la eficacia anestésica de los complejos de inclusión de la mezcla enantiomérica de la bupivacaína (S75-R25) y de la bupivacaína racémica (S50-R50) con hidroxipropilb-ciclodextrina (HPb-CD) comparándolos con las preparaciones actualmente utilizadas en la clínica. MÉTODO: Los complejos de inclusión fueron preparados mezclándose cantidades apropiadas de HPb-CD y S50-R50 ó S75-R25 en las razones molares (1:1 y 1:2) y caracterizados por estudios de solubilidad de fases. Se determinaron las constantes de afinidad (K) de cada AL por la HPb-CD. Los bloqueos motor y sensorial inducidos por las drogas libres y complejadas fueron evaluados en ratones, a través del bloqueo del nervio ciático. Para la realización de los experimentos, se utilizaron tres concentraciones de AL: 0,125; 0,25 y 0,5%. RESULTADOS: Los estudios de solubilidad indicaron la formación de complejos de inclusión de S50-R50 y S75-R25 con HPb-CD, con valores de constante de afinidad (K) análogos para los dos anestésicos: 14,7 M-1 (S50-R50: HP-bCD) y 14,3 M-1 (S75-R25: HP-bCD). Las pruebas en animales mostraron que la complejidad potenció el bloqueo nervioso diferencial inducido por los AL: i) la duración del bloqueo motor inducido por S75-R25 fue análogo al del S50-R50, pero menos intenso (p < 0,001). Ya los complejos, S50-R50HPb-CD y S75-R25 HPb-CD redujeron la latencia (p < 0,01 y p < 0,05, respectivamente) sin modificar la intensidad del bloqueo motor (Emáx), con relación a las drogas libres; ii) la evaluación del bloqueo sensorial mostró un aumento en la intensidad de la analgesia con los sistemas S50-R50 HPb-CD (2 veces, p < 0,001) y S75-R25 HPb-CD (1,5-1,8 veces; p < 0,01 y p < 0,001, respectivamente), en las dos proporciones molares (1:1 y 1:2, AL:CD), además del prolongamiento de la duración del efecto analgésico, cuando comparados a las formulaciones S50-R50 y S75-R25. CONCLUSIONES: Los efectos analgésicos más pronunciados logrados después de la complexación con HPb-CD muestran que ambas formulaciones, S50-R50 HPb-CD y S75-R25 HPb-CD, son de grande interés para el alivio del dolor en el período postoperatorio, con la ventaja de ser administradas en menores concentraciones. Mientras, hay que resaltar que la mezcla enantiomérica de bupivacaína (S75-R25), por ser una droga menos tóxica, representa una alternativa en el desarrollo de formulaciones de liberación controlada más seguras y eficaces de que con la bupivacaína racémica (S50-R50).31632

Physico-chemical characterization of inclusion complex between hydroxymethylnitrofurazone and hydroxypropyl-beta-cyclodextrin

Hydroxymethylnitrofurazone (NFOH) is a prodrug that is active against Trypanosoma cruzi. It however presents low solubility and high toxicity. Hydroxypropyl-beta-cyclodextrin (HP-beta-CD) can be used as a drug-delivery system for NFOH modifying its physico-chemical properties. The aim of this work is to characterize the inclusion complex between NFOH and HP-beta-CD. The rate of NFOH release decreases after complexation and thermodynamic parameters from the solubility isotherm studies revealed that a stable complex is formed (deltaGº= 1.7 kJ/mol). This study focuses on the physico-chemical characterization of a drug-delivery formulation that comes out as a potentially new therapeutic option for Chagas disease treatment.FAPESPCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

Lipid nanostructured carriers systems for ivermectin and methoprene aiming parasite control

The study of characteristics of nanoscale structures and applications now has great interest of researchers from different areas. In this regard, lipid carriers can improve the bioavailability of drugs and the reduction of possible toxicological effects. Thus, the development of nanostructured systems for the agricultural sector, aimed at combating parasites may reduce extensive damage caused to livestock producers and animal health. This study aimed to prepare and characterize lipid carrier systems, such as Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC), as well as evaluate the potential of cyto and genotoxicity of these systems in order to improve and produce alternatives to the use targeting these compounds in veterinary applications. Lipid nanoparticles had become spherical with an average size of 250 nm and remained stable over 120 days. The encapsulation efficiency was greater than 99% for both drugs and release tests showed a strong interaction between drugs and nanoparticles. Cyto- and genotoxicity tests show that nanoparticles made possible changes in cellular viability of the tested cells. Thus, the results showed that the nanoparticles had good colloidal characteristics without changes in its characteristics, enabling the development of carrier systems for these drugs , aiming veterinary applications39910341043FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP#2013/12322-2; #2015/15617-9; #2013/24788-

Pharmacokinetic Profile of Liposome-Encapsulated Ropivacaine after Maxillary Infiltration Anaesthesia

O objetivo do presente estudo foi determinar os parâmetros farmacocinéticos da ropivacaína encapsulada em lipossomas após anestesia local em 14 voluntários sadios. Neste estudo randomizado, cruzado e duplo-cego, os voluntários receberam anestesia infiltrativa na maxila de ropivacaína a 0,5% encapsulada em lipossomas e ropivacaína 0,5% com epinefrina a 1:200.000 em duas sessões distintas. Amostras de sangue foram coletadas antes e após (de 15 a 1440 min) a administração das formulações de ropivacaína. A quantificação da concentração plasmática de ropivacaína foi feita por meio de HPLC com detecção por UV. Os parâmetros farmacocinéticos AUC 0-24 (área sob a curva de concentração × tempo do tempo 0 até 24 horas) , AUC 0-∞ (área sob a curva de concentração x tempo do tempo 0 até o infinito), C max (concentração máxima da droga), CL (clearance renal), T max (tempo em que ocorre a concentração máxima); t 1/2 (meia vida de eliminação) e V d (volume de distribuição) foram analisados pelo teste de Wilcoxon. Nenhuma diferença (p &gt; 0,05) foi observada entre as duas formulações em cada parâmetro farmacocinético avaliado e as concentrações plasmáticas de ropivacaína, considerando cada período de tempo. Ambas as formulações apresentaram perfil farmacocinético semelhante, indicando que a formulação lipossomal poderia ser uma opção mais segura para o uso deste anestésico local, devido à ausência de vasoconstritor. The aim of this study was to determine the pharmacokinetic parameters of liposomal ropivacaine after dental anesthesia in 14 healthy volunteers. In this randomized, double-blind and crossover study, the volunteers received maxillary infiltration of liposome-encapsulated 0.5% ropivacaine and, 0.5% ropivacaine with 1:200,000 epinephrine in two different sessions. Blood samples were collected before and after (from 15 to 1440 min) the administration of either ropivacaine formulation. HPLC with UV detection was used to quantify plasma ropivacaine concentrations. The pharmacokinetic parameters AUC 0-24 (area under the plasma concentration × time curve from baseline to 24 h), AUC 0-∞ (area under the plasma concentration-time curve from baseline to infinity), C max (maximum drug concentration), CL (renal clearance), T max (maximum drug concentration time), t 1/2 (elimination half-life) and Vd (volume of distribution) were analyzed using the Wilcoxon signed-rank test. No differences (p &gt; 0.05) were observed between both formulations for any of the pharmacokinetic parameters evaluated and plasma ropivacaine concentrations, considering each period of time. Both formulations showed similar pharmacokinetic profiles, indicating that the liposomal formulation could be a safer option for use of this local anesthetic, due to the absence of a vasoconstrictor. Keywords: ropivacaine, local anesthesia, dentistry, liposome, pharmacokinetic Pharmacokinetic Profile of Liposome-encapsulated Ropivacaine after Maxillary Infiltration Anaesthesia J. Braz. Chem. Soc. 1946 Introduction Prolonged-action local anesthetic is required when postoperative pain and discomfort are expected, especially after major surgical procedures. 1 In many countries, bupivacaine, the racemic mixture of S-and D-bupivacaine, is the only long-acting local anesthetic available in dental practice. Ropivacaine (RVC), another long-acting local anesthetic of the cyclic aminoamide family, is synthesized in the S-enantiomer form and presents lower toxicity to the cardiovascular and central nervous systems, compared to bupivacaine. 2 Traditionally, most of local anesthetic formulations are administered together with a vasoconstrictor in order to increase anesthesia duration and to reduce systemic absorption rate. 3 It was recently demonstrated that the use of these formulations increased, especially those containing epinephrine 1:100.000. 5 Alternative drug delivery systems, such as liposomes, have been used to prolong the duration of action of many drugs, including local anesthetics. 6-10 These vesicles are nontoxic and nonimmunogenic because their components (phosphatidyl choline and cholesterol) are also found in biological membranes. 17 Previous authors have shown that liposomal encapsulation of bupivacaine altered its pharmacokinetic profile after extradural injection in rabbits, resulting in lower concentrations of the drug in plasma, liver and myocardium. 18 Grant and co-workers 16 observed that when encapsulated in liposomes, bupivacaine remained at the injection site for a significantly longer period of time after subcutaneous injection in mice. Attempting to simulate an accidental intravascular injection of a local anesthetic, Boogaerts and coworkers 8 assessed the acute CNS (central nervous system) and cardiac toxicities induced by intravenous infusion in rabbits of 0.25% bupivacaine, with and without epinephrine (1:200,000), compared to liposomeencapsulated bupivacaine. They demonstrated a reduction of CNS and cardiac toxicities using liposome-encapsulated bupivacaine. The addition of epinephrine to the plain solution did not decrease the CNS and cardiac toxicities induced by bupivacaine. It was recently demonstrated in animal studies, which used sciatic and infraorbital nerve blockades, that encapsulation of ropivacaine into unilamellar vesicles increased the duration and the intensity of analgesic effects. 6 Although long-acting local anesthetics are normally used in low doses in dentistry, high doses may be required for removal of four impacted third molars in a single session. The present study is the first attempt to measure the pharmacokinetic parameters of ropivacaine after maxillary infiltration anesthesia using a liposome-encapsulated formulation in healthy volunteers. The pharmacokinetic parameters of an RVC formulation containing epinephrine (vasoconstrictor) were also assessed for comparison. Experimental Materials RVC hydrochloride was donated by Cristalia Prod. Quim. Farm. Ltda (Itapira, SP, Brazil). Egg phosphatidylcholine (EPC), cholesterol (Ch) and α-tocopherol (α-T) were purchased from Sigma Chemical Company (St Louis, MO). All other reagents used were of analytical grade. RVC-liposome formulation The liposomal RVC formulations were prepared as described by Araújo and co-workers. 10 The following liposomal characterization was previously determined by Araújo and co-workers. Subjects This research was approved by the Ethical Committee of Piracicaba Dental School, University of Campinas (approval #164/2006). Fourteen healthy volunteers (seven males and seven females) aged 24 (± 3.1) years old were selected, and signed a written informed consent. The volunteers presented no systemic or oral disorders, had no history of allergy to any of the local anesthetics used, and were not taking any medication, as determined by oral questioning and by their documented health histories. Prior to the beginning and right after the end of the study, all the subjects were submitted to laboratory tests to confirm that they were in good health and that the females were not pregnant. The same tests were performed at the end of the study to ensure that all results previously obtained were not altered by the anesthetic formulations tested. These tests included cross-reactive protein, blood-hemoglobin, lymphocyte count, platelet count, erythrocyte sedimentation rate, serum (S)-sodium, S-potassium, S-chloride, S-albumin, S-alkaline phosphate, S-gamma-glutamyl-transferase, S-aspartate transaminase, S-alanine transaminase, S-creatine, plasma glucose, urea, cholinesterase, total protein, bilirubin, uric acid, urine glucose, urine leukocyte count, urine protein, and urine hemoglobin. Serology tests for human immunodeficiency virus and hepatitis B and C were also performed. Female subjects underwent a urine bHCG pregnancy test. Ambulatory procedures Anesthetic procedures In this double-blind and crossover study, the volunteers randomly received 1.8 mL of 0.5% ropivacaine with 1:200,000 epinephrine, and liposome-encapsulated 0.5% ropivacaine, for infiltration anesthesia at the apex of the right maxillary canine, in two different sessions spaced one week apart. Ropivacaine with 1:200,000 epinephrine was obtained by simple dilution of the commercially available solution of ropivacaine (Naropin ® 10 mg mL -1 , AstraZeneca, São Paulo, Brazil) immediately before application. Under sterile conditions, 5 mL of 1% ropivacaine was diluted with 5 mL of 1:100,000 (v/v) epinephrine (Drenalin ® , Ariston Ind. Quim. Farm. Ltda, São Paulo, SP, Brazil). The local anesthetics (1.8 mL) were placed into coded sterile 3 mL Luer-Lok syringes (Becton Dickinson, Curitiba, Brazil) fitted with disposable needles (30G, one-inch, Becton-Dickinson Company, Franklin Lakes, NJ, USA). After topical anesthesia on the injection site with 20% benzocaine, the formulations were injected at the maxillary buccal fold of the right-canine region at an injection rate of 1 mL min -1 . The same operator performed the maxillary infiltration anesthesia in all the subjects. Blood sampling and drug analysis Blood samples (4.5 mL) from a forearm vein were collected with a heparinized cannula before and 15, Pharmacokinetic and statistical analyses The following pharmacokinetic parameters were evaluated by computer software (PK Solutions, noncompartmental pharmacokinetics data analysis, 2001; Summit Research Services, Montrose, CO, USA): C max (maximum drug concentration); T max (maximum drug concentration time); AUC 0-24 , (area under the plasma concentration-time curve from baseline to 24 h); AUC 0-∞ (area under the plasma concentration-time curve from baseline to infinity); CL (renal clearance); t 1/2 (elimination half-life) and Vd (volume of distribution). Statistical analysis was performed using the Student&apos;s t-test in order to compare the ropivacaine concentrations between the groups at each time interval. Pharmacokinetic parameters were compared using the Wilcoxon signed-rank test. The significance level was set at 5%, and the tests were performed with BioEstat 5.0 (Fundação Mamirauá, Belém, PA, Brazil) Results and Discussion In an earlier study, Araújo and co-workers 6 demonstrated that the size distribution of liposomal formulations containing RVC presented two modes, one with a maximum at 371 nm (85%), and another with a peak at 128 nm (15%). The efficiency of encapsulation was around 24%, which was sufficient to modify the release profile of the pharmaceutical, with a reduction of the release rate over a one-hour period from 76 to 58%. In the same study it was also shown that, compared to RVC alone, the liposomal RVC formulation increased the duration and intensity of analgesic effects in sciatic and infraorbital nerve blocking experiments. Extending the earlier work of Araújo and co-workers 6 here we report on the first attempt to assess the pharmacokinetic parameters of ropivacaine after maxillary infiltration anesthesia using a liposome-encapsulated ropivacaine formulation in healthy volunteers, comparing the results with a commercial RVC formulation containing epinephrine vasoconstrictor. The calibration curve for determination of plasma ropivacaine ( 22 The detection limit for ropivacaine observed in our study (30 ng mL -1 ) was close to the limit observed by those authors (25 ng mL -1 )