Bupivacaine liposome injectable suspension (Exparel, Pacira Pharmaceuticals, Inc., San Diego, CA, USA) is an extended-release formulation of bupivacaine. It is approved for analgesia via tissue infiltration and interscalene brachial plexus in man, but not for use in neuraxial space. The aim of this study is to establish neurologic and histopathologic outcomes of escalating dosages of liposome bupivacaine suspension administered intrathecally.
Twenty-five pigs, weighing 36.2 ± 4.4 kg, were randomly assigned to one of five groups to receive intrathecal injections of 3 ml 0.9% sodium chloride (negative control), 3 ml 0.5% bupivacaine hydrochloride (positive control), or one of three doses of 1.33% liposome injectable suspension: 1.5, 3 or 5 ml (20, 39 or 66 mg). After recovering from general anaesthesia, the pigs were assessed for neurological outcome study by blinded observers. Three weeks later, the animals were sacrificed for histopathologic evaluations of neurotoxicity. The samples of cerebrospinal fluid were analysed before the application of tested substances and three weeks later.
Pigs that received 0.9% sodium chloride, bupivacaine hydrochloride 3 ml or 1.5 ml of 1.33% (20 mg) liposome bupivacaine recovered within 2, 5 and 4 hours, respectively. Pigs that received 3 and 5 ml of 1.33% (39 and 66 mg) liposome bupivacaine, respectively, exhibited signs of neuraxial block up to 32 hours after injection. No histopathologic evidence of neurotoxicity was found in any of the groups, results of the cerebrospinal fluid analysis were inconclusive.
Intrathecal administration of liposome bupivacaine injectable suspension in pigs resulted in a dose-response pattern of longer duration of neuraxial block than bupivacaine hydrochloride without histopathologic evidence of neurotoxicity.
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