Efficacy of sustained-release novel bupivacaine formulations in sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies (MVS) Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
The objective of this thesis was to prepare and assess several formulations of the local
anaesthetic bupivacaine to achieve a longer duration of action. Intralipid® emulsion (a soybean
oil emulsion) and collagen combined with titanium oxide nanoparticles were used to develop
slow release bupivacaine formulation. These formulations were tested both in vitro as a pilot
study and in vivo in sheep.
Collagen was extracted from bovine limed split hide (a by-product of the leather industry). The
collagen as a 1% solution was mixed with bupivacaine hydrochloride 0.5% aqueous solution
(Marcain® 0.5%, AstraZeneca, New Zealand) giving a final concentration of 0.25% bupivacaine.
Intralipid® (20%, Fresenius Kabi Australia) and bupivacaine 0.5% were mixed resulting in a 0.25%
bupivacaine lipid emulsion. Both formulations were tested in vitro pilot study for the release of
bupivacaine through a dialysis membrane. The concentration of bupivacaine in the dialysate was
measured using High-Performance Liquid Chromatography (HPLC). In the animal studies, 18
sheep were used to compare bupivacaine (control) and bupivacaine-Intralipid®, and another 18
sheep for commercial bupivacaine (control) and collagen- bupivacaine. Each sheep received a
nerve block using the control or test formulation in each forelimb. The nerve block was placed at
the level of the accessory digits with three injections totalling 4 mL using a 22G needle. The
efficacy was tested by manually applying a mechanical noxious stimulus with a blunt instrument
below the level of the block. This test was performed first after 15 min and then at one-hour
intervals. The time at which a response was observed was considered as the end-point for that
In the in vitro pilot study, both collagen and Intralipid®-based formulations showed slightly more
sustained release compared to the control group. However, collagen-based formulation of
bupivacaine had the most sustained-release among all.
In the sheep study, the Intralipid®-based formulation significantly extended the duration of the
nerve block compared to the control group (P<0.05). On the contrary, the collagen-based
formulation of bupivacaine shortened the duration of action significantly compared to control
In conclusion, an Intralipid®-based formulation provided a more sustained action after nerve
blocks in the sheep metacarpal region compared to aqueous bupivacaine or the collagen based
formulation. Further research on structure and activity of collagen and its interactions with
bupivacaine is required to develop a longer acting formulation.