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

Abstract

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.

Pharmacokinetic profile of liposome-encapsulated ropivacaine after maxillary infiltration anaesthesia

“…6 Briefly, EPC-Ch-α-T (4:3:0.07, molar ratio) films were obtained by evaporating stock chloroform solutions under a stream of wet nitrogen, followed by vacuum for 2 h. Films were suspended in HEPES buffer (20 mmol L -1 , 154 mmol L -1 NaCl, pH 7.4), and multilamellar vesicles were obtained after vortexing at ambient temperature (5 min, 25 °C). Large unilamellar vesicles were prepared by extrusion (15 cycles) of the multilamellar vesicles within 400 nm membrane filters (25 °C), using a Lipex Biomembranes Inc. (Vancouver, Canada) extruder.…”

“…10 The following liposomal characterization was previously determined by Araújo and co-workers. 6 The mean diameter and size distribution analysis, performed Franz-Montan et al 1947 Vol. 21, No.…”

“…5 Alternative drug delivery systems, such as liposomes, have been used to prolong the duration of action of many drugs, including local anesthetics. 6 Liposomes are phospholipid vesicles that have been demonstrated to be effective drug carriers, improving the effectiveness and reducing the toxicity of anesthetics in both cardiovascular and central nervous systems. [6][7][8][9][10] These vesicles are nontoxic and nonimmunogenic because their components (phosphatidyl choline and cholesterol) are also found in biological membranes.…”

“…6 Liposomes are phospholipid vesicles that have been demonstrated to be effective drug carriers, improving the effectiveness and reducing the toxicity of anesthetics in both cardiovascular and central nervous systems. [6][7][8][9][10] These vesicles are nontoxic and nonimmunogenic because their components (phosphatidyl choline and cholesterol) are also found in biological membranes. 11 These characteristics have been demonstrated in vivo (animal models) for liposomeencapsulated bupivacaine using multilamellar vesicles, [12][13][14][15][16] and large unilamellar vesicles.…”

“…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. 19 According to Zink and Graf, 20 ropivacaine seems to have the greatest margin of safety of all the long-acting local anesthetics, and could be useful in lengthy dental procedures.…”