Neurotoxicological assessment after intracisternal injection of liposomal bupivacaine in rabbits

Anti-nociceptive effects of bupivacaine-encapsulated PLGA nanoparticles applied to the compressed dorsal root ganglion in mice

Bupivacaine is a commonly used local anesthetic in postoperative pain management. We evaluated the effects of a prolonged, local delivery of bupivacaine on pain behavior accompanying a chronic compression of the dorsal root ganglion (CCD) - an animal model of radicular pain. Poly(lactide-coglycolide) (PLGA) nanoparticles encapsulating bupivacaine were injected unilaterally into the L3 and L4 DRGs of mice just before producing CCD by implanting a stainless-steel rod in the intervertebral foramen of each ganglion. Behavioral sensitivity to punctate mechanical stimuli (Von Frey filaments) of different forces of indentation, delivered to each hind paw, was measured before and on subsequent days of testing after the CCD. Nanoparticles were spherical in morphology and 150 ± 10 nm in diameter. Bupivacaine was steadily released as measured in vitro over 35 days. A dye that was encapsulated in the nanoparticles was found in the intact DRG after 2 weeks. CCD alone or with injection of blank (control) nanoparticles produced a behavioral hypersensitivity to the punctate stimuli on the ipsilateral paw without affecting sensitivity on the contralateral, over a period of 7-14 days. The hypersensitivity was manifested as an increased incidence of paw-withdrawal to indentation forces normally below threshold (allodynia) and an increased shaking to a filament force that always elicited withdrawal prior to CCD (hyperalgesia). In contrast, nanoparticles with bupivacaine prevented any manifestation of allodynia or hyperalgesia on the ipsilateral hind paw while leaving normal nociceptive responses largely intact on both hind paws. CCD induced behavioral hypersensitivity to nociceptive stimuli is known to be associated with a hyperexcitability of sensory neurons originating in the compressed ganglion. We hypothesize that bupivacaine-loaded PLGA nanoparticles may prevent the occurrence of this neuronal hyperexcitability without reducing the nociceptive information normally conducted from the periphery to the central nervous system. The slow, sustained delivery of bupivacaine by nanoparticles may provide a means of preventing the occurrence of postoperative neuronal hyperexcitability that could develop into chronic neuropathic pain.

Release Pattern of Liposomal Bupivacaine in Artificial Cerebrospinal Fluid

OBJECTIVE

We aimed to compare the possible controlled release profile of multilamellar liposomal bupivacaine formulations with non-liposomal forms in artificial cerebrospinal fluid (CSF) under in vitro conditions.

METHODS

Liposome formulations were prepared using a dry-film hydration method. Then, an artificial CSF-buffered solution was prepared. Bupivacaine base with liposomal bupivacaine base, bupivacaine HCl with liposomal bupivacaine HCl and bupivacaine HCl were added in a Franz diffusion cell. These solutions were kept in a hot water bath for 24 h. The samples were taken at 0.5, 1, 3, 6, 12 and 24 h (1st series of experiment). Solutions of bupivacaine base with liposomal bupivacaine base and bupivacaine HCl with liposomal bupivacaine HCl were centrifuged to obtain liposomal bupivacaine base and liposomal bupivacaine HCl. Afterwards, liposomal bupivacaine base and liposomal bupivacaine HCl were added in a Franz diffusion cell. After keeping these solutions in a hot water bath for 24 h as well, the samples were taken at the same time intervals (2(nd) series of experiment). All samples (54 from the 1st experiment and 36 from the 2(nd) experiment) were analysed with high-performance liquid chromatography and ultra-performance liquid chromatography and their chromatograms were obtained.

RESULTS

After obtaining calibration curves for bupivacaine base and HCl, release patterns of these formulations were plotted. A markedly controlled slow-release pattern was observed for multilamellar liposomal bupivacaine than for non-liposomal bupivacaine in artificial CSF.

CONCLUSION

Demonstration of controlled slow-release profile for mutilamellar liposomal bupivacaine in artificial CSF in vitro might support intrathecal use of liposomal bupivacaine in vivo in animal studies.

The Safety of EXPAREL ® (Bupivacaine Liposome Injectable Suspension) Administered by Peripheral Nerve Block in Rabbits and Dogs

A sustained-release DepoFoam injection formulation of bupivacaine (EXPAREL, 15 mg/mL) is currently being investigated for postsurgical analgesia via peripheral nerve block (PNB). Single-dose toxicology studies of EXPAREL (9, 18, and 30 mg/kg), bupivacaine solution (Bsol, 9 mg/kg), and saline injected around the brachial plexus nerve bundle were performed in rabbits and dogs. The endpoints included clinical pathology, pharmacokinetics, and histopathology evaluation on Day 3 and Day 15 (2/sex/group/period). EXPAREL resulted in a nearly 4-fold lower C_max versus Bsol at the same dose. EXPAREL was well tolerated at doses up to 30 mg/kg. The only EXPAREL-related effect seen was minimal to mild granulomatous inflammation of adipose tissue around nerve roots (8 of 24 rabbits and 7 of 24 dogs) in the brachial plexus sites. The results indicate that EXPAREL was well tolerated in these models and did not produce nerve damage after PNB in rabbits and dogs.