Hybrid Hydrogel Composed of Polymeric Nanocapsules Co-Loading Lidocaine and Prilocaine for Topical Intraoral Anesthesia.

This study reports the development of nanostructured hydrogels for the sustained release of the eutectic mixture of lidocaine and prilocaine (both at 2.5%) for intraoral topical use. The local anesthetics, free or encapsulated in poly(ε-caprolactone) nanocapsules, were incorporated into CARBOPOL hydrogel. The nanoparticle suspensions were characterized in vitro in terms of particle size, polydispersity, and surface charge, using dynamic light scattering measurements. The nanoparticle concentrations were determined by nanoparticle tracking analysis. Evaluation was made of physicochemical stability, structural features, encapsulation efficiency, and in vitro release kinetics. The CARBOPOL hydrogels were submitted to rheological, accelerated stability, and in vitro release tests, as well as determination of mechanical and mucoadhesive properties, in vitro cytotoxicity towards FGH and HaCaT cells, and in vitro permeation across buccal and palatal mucosa. Anesthetic efficacy was evaluated using Wistar rats. Nanocapsules were successfully developed that presented desirable physicochemical properties and a sustained release profile. The hydrogel formulations were stable for up to 6 months under critical conditions and exhibited non-Newtonian pseudoplastic flows, satisfactory mucoadhesive strength, non-cytotoxicity, and slow permeation across oral mucosa. In vivo assays revealed higher anesthetic efficacy in tail-flick tests, compared to a commercially available product. In conclusion, the proposed hydrogel has potential for provision of effective and longer-lasting superficial anesthesia at oral mucosa during medical and dental procedures. These results open perspectives for future clinical trials.

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)-ß-cyclodextrin (ß-CD) complex liberation to membranes was provided by studying the architectural supramolecular arrangements of PLC, ß-CD and egg phosphatidylcholine (EPC) liposomes, a membrane model. The topologies and possible interactions of mixtures of PLC, ß-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/ß-CD/EPC at pH 10 the PLC molecules are almost totally embedded into the liposomes and little interaction was observed between PLC and ß-CD. However, at pH 5.5 not only was PLC imbedded in the EPC bilayer, but PLC was also interacting with ß-CD. These results were rationalized as a spontaneous PLC release from ß-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.

Liposome-prilocaine interaction mapping evaluated through STD NMR and molecular dynamics simulations.

We have examined the interaction of the neutral and protonated species of the local anesthetic prilocaine (PLC) with phosphatidylcholine (PC) bilayers combining experimental ((1)H NMR) and theoretical (molecular dynamics simulations) approaches. DOSY experiments allowed the determination of the association constants of protonated (Ka = 9 L/mol) and neutral (Ka = 21 L/mol) PLC to egg PC liposomes. Saturation transfer difference (STD) experiments showed a different trend depending on pH: At high pH the PLC hydrogen saturation was essentially uniform and at pH 5.5 the experiments show an enhancement of the aromatic moiety hydrogen saturation, with respect to the tail. Molecular dynamics simulations, performed with PLC molecules on planar bilayers of palmitoyloleyl-PC, revealed a preferential orientation for the protonated PLC species at the polar interface of the bilayer, and a nonoriented and deeper insertion for neutral PLC. Such preferential location of protonated and neutral PLC inside the bilayer can be described as different transient sites which could modulate the access of these molecules to their binding site(s) in the voltage-gated sodium channel, justifying differences in the anesthetic's potency upon ionization.

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.

Liposomal formulations of prilocaine, lidocaine and mepivacaine prolong analgesic duration.

PURPOSE: A 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. METHODS: Large 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. RESULTS: The 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). CONCLUSIONS: These 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.

Diffusion of Ca(OH)2 associated with different vehicles: chromatographic study (high-performance liquid chromatography).

Using high-performance liquid chromatography (HPLC), small amounts of liquid samples in which 25 premolar human teeth were immersed were evaluated. Each tooth was immersed separately in 800-ml flasks with distilled ultra-pure deionized water and remained there for 1678 h after the filling of their canals with Ca(OH)2 associated with different vehicles: group 1: polyethylene glycol and colophon (Calen); group 2: glycerin and camphorated paramonochlorophenol; group 3: camphorated paramonochlorophenol; group 4: glycerin and tricresol formol; and group 5: anesthetic solution (Citanest). Five polyethylene tubes were filled with each of these pastes and placed unsealed in similar flasks. At the end of this period, HPLC analyses of the aqueous medium related to each group were performed to detect other substances that had diffused from the pastes used in the canals of the teeth other than calcium and hydroxyl ions. Although the groups presented different maximum peaks when there was no barrier, they all showed higher values than when the tooth was present. At least 15 substances other than Ca2+ and OH- were detected in the aqueous medium of group 4. Analyzing the HPLC graphs, we concluded that not only Ca2+ and OH-, but also a considerable quantity of other components of the pastes diffused through the dentine and reached the external root surface.