Analgesic duration and kinetics of liposomal bupivacaine after subcutaneous injection in mice.

1. The objective of the present study was to assess the time-course profile of analgesia and bupivacaine concentrations at the site of injection after subcutaneous administration of a single dose of standard bupivacaine or a novel controlled-release liposomal bupivacaine formulation. 2. Groups of mice were injected subcutaneously with 0.2 mL of 0.5% standard bupivacaine or 0.5, 1 or 2% liposomal bupivacaine. 3. A prolonged duration of analgesia occurred in mice receiving liposomal bupivacaine. In the liposomal groups, the bupivacaine remained at the injection site for more than 96 h, compared with approximately 8 h in groups injected with standard bupivacaine. 4. These results confirm that the prolonged analgesia observed after injection of the liposomal formulation is associated with sustained higher levels of bupivacaine at the site of injection.