Pre-clinical evaluation of new dibucaine formulations for preventive analgesia.

We have previously developed ammonium sulphate gradient loaded liposomes to encapsulate dibucaine. Thus, the purpose of this study was to evaluate the pre-clinical safety and effectiveness of this novel ionic liposomal formulation of dibucaine (DBC), as described in previous work. Effectiveness was evaluated in vivo on Wistar rats (n = 8) that received plain DBC or liposomal DBC (DBCLUV). Control empty liposomes (without DBC) or saline were also used as control. Sciatic nerve block was performed using the formulations or controls (0.4 mL). A hindpaw incision-based postoperative pain model was used to evaluate mechanical hypersensitivity with von Frey filaments. To verify antiinflamatory activity protein levels of TNF-α, IL-1ß, substance P and CGRP were measured by ELISA in the hindpaw tissue after 1 and 6 hours of the incision. To corroborate drug safety, sciatic nerve Schwann cell cultures were treated with the aforementioned formulations and assessed for cell viability (MTT assay) and death (flow cytometry assay). Histopathology of the tissues surrounding the sciatic nerve region was also assessed 2 and 7 days after treatment. All animals presented post incisional hypersensitivity and DBCLUV showed longer analgesic effect (p < 0.001). DBCLUV reduced TNF-α and CGRP levels (p < 0.05). Histopathological evaluation showed greater inflammatory reaction after the administration of control liposomes when compared to DBC (p < 0.05). There was no difference in Schwann cell viability and death between plain and encapsulated DBC. DBCLUV was safe and enhanced anaesthesia duration due to slow release of dibucaine from ammonium sulphate gradient loaded liposomes.

Efficacy of liposome-encapsulated mepivacaine for infiltrative anesthesia in volunteers.

This blinded crossover study evaluated the efficacy and pain sensitivity evoked by a previously reported liposome-encapsulated mepivacaine formulation (Araujo et al., 2004). Thirty healthy volunteers received an intraoral injection (1.8 mL), at four different sessions, of the following formulations: 2% mepivacaine with 1:100,000 epinephrine (MVC(2%EPI)), 3% mepivacaine (MVC(3%)), and 2 and 3% liposome-encapsulated mepivacaine (MVC(2%LUV) and MVC(3%LUV)). Latency period and duration of anesthesia were assessed by an electrical pulp tester and injection discomfort by a visual analog scale (VAS). Data were analyzed with Tukey-Kramer and Friedman tests (P < 0.05). No significant difference was found regarding latency period (in minutes) among the formulations (P > 0.05). The duration of anesthesia after the injection of MVC(3%LUV) was higher than the one obtained after the infiltration of MVC(2%LUV) and of MVC(3%) (P < 0.05). However, the duration of anesthesia obtained with MVC(3%) did not differ from the one obtained with MVC(2%LUV) (P > 0.05). MVC(3%LUV) showed lower VAS median values than MVC(2%EPI) (P < 0.05), and there were no significant differences among the others formulations. Liposome-encapsulated 3% mepivacaine showed longer duration of anesthesia, in comparison to the commercial formulation of MVC(3%). MVC(2%LUV) was able to produce a similar duration of anesthesia as the 3% commercial formulation, despite the 50% decrease in the anesthetic concentration. Thus, the encapsulation of mepivacaine increased the duration of anesthesia and reduced the injection discomfort caused by vasoconstrictor-associated formulations in healthy volunteers.

Improved efficacy of naproxen-loaded NLC for temporomandibular joint administration.

Inflammatory conditions of the temporomandibular joint (TMJ) and peripheral tissues affect many people around the world and are commonly treated with non-steroidal anti-inflammatory drugs (NSAIDs). However, in order to get desirable results, treatments with NSAIDs may take weeks, causing undesirable side effects and requiring repeated administration. In this sense, this work describes the development of an optimized nanostructured lipid carrier (NLC) formulation for intra-articular administration of naproxen (NPX). An experimental design (23) selected the best formulation in terms of its physicochemical and structural properties, elucidated by different methods (DLS, NTA, TEM, DSC, and ATR-FTIR). The chosen formulation (NLC-NPX) was tested on acute inflammatory TMJ nociception, in a rat model. The optimized excipients composition provided higher NPX encapsulation efficiency (99.8%) and the nanoparticles were found stable during 1 year of storage at 25 °C. In vivo results demonstrated that the sustained delivery of NPX directly in the TMJ significantly reduced leukocytes migration and levels of pro-inflammatory cytokines (IL-1ß and TNF-α), for more than a week. These results point out the NLC-NPX formulation as a promising candidate for the safe treatment of inflammatory pain conditions of TMJ or other joints.

Development and pharmacological evaluation of ropivacaine-2-hydroxypropyl-beta-cyclodextrin inclusion complex.

Ropivacaine (RVC) is an enantiomerically pure local anesthetic (LA) largely used in surgical procedures, which presents physico-chemical and therapeutic properties similar to those of bupivacaine (BPV), but associated to less systemic toxicity. This study focuses on the development and pharmacological evaluation of a RVC in 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) inclusion complex. Phase-solubility diagrams allowed the determination of the association constant between RVC and HP-beta-CD (9.46 M(-1)) and showed an increase on RVC solubility upon complexation. Release kinetics revealed a decrease on RVC release rate and reduced hemolytic effects after complexation (onset at 3.7 mM and 11.2mM for RVC and RVC HP-beta-CD, respectively) were observed. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and X-ray analysis (X-ray) showed the formation and the morphology of the complex. Nuclear magnetic resonance (NMR) and job-plot experiments afforded data regarding inclusion complex stoichiometry (1:1) and topology. Sciatic nerve blockade studies showed that RVC HP-beta-CD was able to reduce the latency without increasing the duration of motor blockade, but prolonging the duration and intensity of the sensory blockade (p<0.001) induced by the LA in mice. These results identify the RVC HP-beta-CD complex as an effective novel approach to enhance the pharmacological effects of RVC, presenting it as a promising new anesthetic formulation.

Benzocaine complexation with p-sulfonic acid calix[n]arene: experimental ((1) H-NMR) and theoretical approaches.

The aim of this work was to study the interaction between the local anesthetic benzocaine and p-sulfonic acid calix[n]arenes using NMR and theoretical calculations and to assess the effects of complexation on cytotoxicity of benzocaine. The architectures of the complexes were proposed according to (1) H NMR data (Job plot, binding constants, and ROESY) indicating details on the insertion of benzocaine in the cavity of the calix[n]arenes. The proposed inclusion compounds were optimized using the PM3 semiempirical method, and the electronic plus nuclear repulsion energy contributions were performed at the DFT level using the PBE exchange/correlation functional and the 6-311G(d) basis set. The remarkable agreement between experimental and theoretical approaches adds support to their use in the structural characterization of the inclusion complexes. In vitro cytotoxic tests showed that complexation intensifies the intrinsic toxicity of benzocaine, possibly by increasing the water solubility of the anesthetic and favoring its partitioning inside of biomembranes.

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.

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.

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 (MVC(2%EPI) ), 3% MVC (MVC(3%) ), 2% and 3% liposome-encapsulated MVC (MVC(2%LUV) and MVC(3%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 (AUC(0-360) and AUC(0-∞)) after MVC(2%LUV) and MVC(2%EPI) injections were smaller (P < 0.05) than the equivalent figures for MVC(3%) and MVC(3%LUV). The time to maximum plasma concentration (Tmax) and the half-life of elimination (t½beta) obtained after the treatment with MVC(2%LUV), MVC(2%EPI), MVC(3%) and MVC(3%LUV) presented no statistically significant differences (P > 0.05). Cmax, AUC(0-360) and AUC(0-∞) after injection of the 2% formulations (MVC(2%LUV) and MVC(2%EPI) ) did not exhibit statistically significant differences (P > 0.05). The pharmacokinetics of MVC(2%LUV) were comparable to the pharmacokinetics of MVC(2%EPI). CONCLUSION: The liposomal formulation of 2% MVC exhibits similar systemic absorption to the local anesthetic with vasoconstrictor.

Sufentanil-2-hydroxypropyl-ß-cyclodextrin inclusion complex for pain treatment: physicochemical, cytotoxicity, and pharmacological evaluation.

Sufentanil (SUF) is a synthetic analgesic opioid widely used for the management of acute and chronic pain. This drug was complexed with 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD) and the physicochemical characterization, in vitro/ex vivo toxicity assays, and pharmacological evaluation were performed. Differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR) analysis, and X-ray powder diffraction showed the formation and the morphology of the complex. Nuclear magnetic resonance afforded data regarding inclusion complex stoichiometry (1:1) with an association binding constant (K(a)) value of 515.2 ± 1.2 M(-1) between SUF and HP-ß-CD. Complexation with HP-ß-CD protected SUF from light exposure and increased its photostability. Release kinetics revealed a decrease in SUF release rate (K(rel) = 7.05 ± 0.52 and 5.61 ± 0.39 min(-1/2) for SUF-HP-ß-CD and SUF, respectively) and reduced hemolytic or myotoxic effects after complexation. Time course of tail-flick test showed that the duration of analgesia induced by SUF (150.0 ± 34.6 min) was significantly increased (p < 0.001) after complexation with HP-ß-CD (355.7 ± 47.2 min) when injected at the same dose (1 µg kg(-1)), prolonging the duration of analgesia after intramuscular administration and representing an alternative on the development of effective and safe drug-delivery system for opioid analgesics.

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.

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

PURPOSE: Liposomal formulations of local anesthetics (LA) are able to control drug-delivery in biological systems, prolonging their anesthetic effect. This study aimed to prepare, characterize and evaluate in vivo drug-delivery systems, composed of large unilamellar liposomes (LUV), for bupivacaine (BVC) and mepivacaine (MVC). METHODS: BVC and MVC hydrochloride were encapsulated into LUV (0.4 micro m) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07 molar ratio) to final concentrations of 0.125, 0.25, 0.5% for BVC and 0.5, 1, 2% for MVC. Motor function and antinociceptive effects were evaluated by sciatic nerve blockade induced by liposomal and plain formulations in mice. RESULTS: Liposomal formulations modified neither the intensity nor the duration of motor blockade compared to plain solutions. Concerning sensory blockade, liposomal BVC (BVC(LUV)) showed no advantage relatively to the plain BVC injection while liposomal MVC (MVC(LUV)) improved both the intensity (1.4-1.6 times) and the duration of sensory blockade (1.3-1.7 times) in comparison to its plain solution (P < 0.001) suggesting an increased lipid solubility, availability and controlled-release of the drug at the site of injection. CONCLUSION: MVC(LUV) provided a LA effect comparable to that of BVC. We propose MVC(LUV) drug delivery as a potentially new therapeutic option for the treatment of acute pain since the formulation enhances the duration of sensory blockade at lower concentrations than those of plain MVC.