Franz Legros

Epidural administration of liposome associated bupivacaine for the management of postsurgical pain: A first study

STUDY OBJECTIVES To explore the influence of liposomes on the pharmacodynamic action of bupivacaine and to determine whether postsurgical analgesic advantages can be obtained from epidural delivery of liposomal bupivacaine compared with the current formulation. DESIGN Open, nonrandomized study. SETTING Physiopathology laboratory, general operating theaters, and intensive care units of Reine Fabiola Hospital and Institut Médical de Traumatologie et Revalidation. PATIENTS 26 ASA physical status II and III patients who had undergone major surgery (abdominal, vascular, urologic, thoracic, orthopedic). INTERVENTIONS After completion of the operation, the patients were divided into 2 groups to receive 1 of 2 bupivacaine preparations epidurally for postsurgical pain: Group 1 (n = 12) received plain 0.5% bupivacaine with 1:200,000 epinephrine; Group 2 (n = 14) received liposomal 0.5% bupivacaine. MEASUREMENTS AND MAIN RESULTS The following observations were made: onset and quality of analgesia, quality of motor block according to the Bromage scale, and sympathetic block. Onset time of sensory block averaged 15 minutes in both groups. Pain relief durations were 3.2 +/- 0.4 hours with plain bupivacaine and 6.25 +/- 1.13 hours with the liposomal preparation (p < 0.05). In the liposomal bupivacaine group, no motor block was recorded. Low sympathetic block occurred in all patients. Analgesia in a subset of patients following abdominal aortic surgery increased from 2.4 +/- 0.35 hours to 10.6 +/- 1.4 hours by encapsulation of bupivacaine (p < 0.01). There was no neurotoxicity or cardiotoxicity. CONCLUSIONS The liposomal formulation of bupivacaine increased duration of analgesia without motor block or adverse side effects.

Toxicity of bupivacaine encapsulated into liposomes and injected intravenously: comparison with plain solutions.

The acute central nervous system and cardiac toxicities of 0.25% bupivacaine, without adrenalin, encapsulated in multilamellar liposomes were compared with 0.25% plain solutions with and without adrenalin after intravenous infusion at a rate of 0.15 mg.kg-1 x min-1 with an increase of 0.036 mg.kg-1 x min-1 every 10 min. Three groups of six anesthetized, unventilated rabbits were studied. The doses of bupivacaine (in mg.kg-1) which produced seizure, ventricular tachycardia, and asystole were determined. The doses of bupivacaine inducing seizure and ventricular tachycardia were significantly higher for liposomal bupivacaine than for the two plain solutions. A statistical comparison of the cumulative lethal doses of bupivacaine 0.25% with adrenalin and of liposomal bupivacaine led to a P = 0.06. Adrenalin did not modify the systemic toxicity of the local anesthetic. This study showed a reduction of nervous and cardiac toxicity of bupivacaine encapsulated in multilamellar liposomes when infused intravascularly.

Plasma concentrations of bupivacaine after brachial plexus administration of liposome-associated and plain solutions to rabbits

Bupivacaine has been associated to multilamellar liposomes with the aim of altering circulating plasma concentrations after injection into the rabbit brachial plexus. Plasma concentrations of bupivacaine have been compared after administration of free drug (BP) or bupivacaine associated to multilamellar liposomes (BP-MLV) made of phosphatidylcholine and cholesterol (molar ratio 4:3). Under light general anaesthesia, one group of six rabbits received an axillary injection of 2.5 mg BP (1 ml, 0.25%), and a second received the same dose of BP-MLV. In both groups3H bupivacaine was used as a marker. The brachial plexus was located using a nerve stimulator. Injection of the anaesthetic solutions invariably prevented the motor response of the paw. The arterial plasma concentrations of bupivacaine were determined after 5 to 240 min and after 24 hr by beta counting. In the MLV population, additional measurements were performed after 48 and 72 hr. The two plasma curves showed a plateau (0.2 μg · ml−1) which was reached after five minutes in the BP group and after 90 min using BP-MLV In the BP-MLV group, the plasma concentrations of bupivacaine were lower during the first ten minutes (P < 0.05), and higher after 24 hr (P < 0.05). Radioactivity decreased between 4 and 24 hr in the BP group and between one and two days in the BP-MLV population. It is concluded that elevated plasma drug concentrations were maintained for longer with BP-MLV than with BP This could prolong the action of the local anaesthetic through a slow release.RésuméLa bupivacaïne a été associée à des liposomes multilamellaires, composés de phosphatidylcholine et cholestérol (rapport molaire 4:3) dans le but de modifier les concentrations plasmatiques de l’anesthésique local après administration au niveau du plexus brachial du lapin. Sous anesthésie générale, un premier groupe (BP) de six lapins a reçu une injection plexique de 1 ml de bupivacaïne commerciale à 0,25% sans adrénaline. Le second groupe (BP-MLV) a reçu 1 ml de bupivacaine liposomale à 0,25%. De la bupivacaine tritiée a été utilisée comme marqueur. Le plexus brachial a été repéré à l’aide d’un stimulateur de nerf. L’injection des solutions anesthésiques fit disparaître les réponses musculaires dans la patte. Les concentrations artérielles de bupivacaïne ont été mesurées à des temps différents (de 5 à 240 minutes et après 24 heures) par comptage de la radioactivité plasmatique et exprimées en μg · ml−1. Dans le groupe MLV, des prélèvements supplémentaires ont été pratiqués après 48 et 72 hr. Les deux courbes plasmatiques montrent un plateau identique (0,2 μg · ml−1), qui est atteint après cinq minutes dans le groupe BP et après 90 min dans le groupe BP-MLV Dans ce dernier groupe, la concentration plasmatique de bupivacaïne était plus basse durant les dix premières minutes (P < 0,05) et plus élevée après 24 hr (P < 0,05). La concentration plasmatique de bupivacaïne diminuait entre 4 et 24 hr dans le groupe BP et après un à deux jours dans le groupe BP-MLV. L’association de la bupivacaïne à des MLV pourrait prolonger la durée d’action de la bupivacaïne administrée au niveau du plexus brachial par le biais d’une libération progressive de l’anesthésique local.

Disposition of liposomal gentamicin following intrabronchial administration in rabbits.

Use of liposomes as carriers of gentamicin for intrabronchial pulmonary delivery was investigated in rabbits. Gentamicin, in isotonic glutamic acid buffer, pH 4.5, was encapsulated in multilamellar vesicles (MLVs) and administered intrabronchially. Higher drug concentrations were found at the pulmonary site of liposome instillation for 1 day as compared with free unencapsulated antibiotic. When time-course distributions of gentamicin given in the liposomal or free form were measured in bronchoalveolar lavages (BAL), similar accumulations were observed up to 4 h, but the drug remained longer (24 h) after administration of the liposomal formulation. Higher amounts of antibiotic were detected in BAL supernatant 1 h after instillation of plain gentamicin; this difference stopped being significant after 4 h. A microbiological assay outlined the bacteriostatic activity of gentamicin released from MLVs and recovered in BAL supernatant. Liposomal gentamicin accumulated in the BAL cell pellet 1 h after intrabronchial instillation; it decreased progressively but minute amounts were still detected after 1 day. On the contrary, no gentamicin was found in the pellet at any time after free drug administration. Comparison of aminoglycoside concentrations in plasma and kidneys indicated lower and constant levels when the liposomal form was instilled. Liposome encapsulation altered the disposition of gentamicin in a way suggesting improved pulmonary concentration and lower systemic toxicity.

Liposome-incorporated dexamethasone palmitate: Chemical and physical properties

Abstract Dexamethasone palmitate (DMP) has been prepared by esterification. This molecule and its isotopic marker have been encapsulated into 20 mg multilamellar liposomes (MLV) and small unilamellar vesicles (SUV) made of egg phosphatidylcholine (egg-PC) alone or of egg-PC and cholesterol (CH) in molar ratios of 4:3 and 4:6. Amounts of DMP ranging from 0.1 to 3000 μg/ml were added to the lipid film. Liposomes were formed in 1 ml phosphate-buffered saline, pH 7.4, 300 mOsm/kg H 2 O. MLV were first isolated by centrifugation. This method proved to be inappropriate, since DMP not only was encapsulated into MLV but also formed micellar structures and aggregates which could not be separated from MLV by centrifugation nor by filtration through a glass microfiber filter. An alternative rapid method was developed, attempting to isolate unencapsulated DMP complexes by minicolumn centrifugation from liposomal suspensions. This method was successfully applied to DMP associated SUV. The encapsulation efficiency was 65% for 4:3 SUV. This fell to 50% for a DMP concentration of 3000 μg/ml. This should be related to a maximal DMP encapsulation of 13 mol% (Fildes and Oliver, J. Pharm. Pharmacol. , 30 (1978) 337–342) which corresponds to 2600 μg/ml under our experimental conditions. The 75% optimum efficiency observed for liposomes made of egg-PC alone suggested that DMP could replace CH in these vesicles. Conformational analysis indicated that DMP inserted into monolayers with its carbonyl group oriented towards the aqueous surface while the aliphatic chain became aligned parallel with the acyl chains of phospholipids. The consideration of the incorporation of DMP into an assembly of phospholipids as taking place in a manner similar to that of CH would appear to be reasonable. This reinforces the validity of the hypothesis of CH being replaced by DMP in liposomes composed of egg PC alone.

Liposome-incorporated Dexamethasone Palmitate Inhibits In-vitro Lymphocyte Response to Mitogen

The use of liposomes for the pulmonary delivery of corticosteroid is an area that is under active investigation. We have recently developed a novel liposomal corticosteroid preparation based on the incorporation of dexamethasone palmitate (DMP) within the bilayer of small unilamellar vesicles (SUVs) made of egg yolk phosphatidylcholine (EPC) and cholesterol; molar ratio EPCC: cholesterol: DMP, 4:3:0.3.

99mTechnetium-stannous oxinate as marker of liposome formulations

Liposomes associated with tin(II) dioxinate were prepared from egg yolk phosphatidylcholine and cholesterol as sterile and pyrogen-free multilamellar or unilamellar vesicles. Complexing of liposomal tin(II) dioxinate with 99mTc attained 98% of the added radioactivity. Thirty percent 99mTc were released during 24-h incubation in biological fluids. The absence of tin colloids seen by electron microscopy and the stability of liposomal phospholipid and tin(II) dioxinate during 72-h incubation at 37 degrees C in plasma and cerebrospinal fluid would allow safe and reliable scintigraphic liposome pharmacokinetic studies.