Local anesthetics prevent painful impulses from reaching the CNS and are often recommended for patients with pain amenable to being controlled via local anesthetic blockades.1-3 In addition to intraoperative analgesia (ie, antinociception during anesthesia), local anesthetics provide postoperative pain relief3; this is critically important because effective postoperative analgesics are limited. NSAIDs (ie, the main drug class used) are effective, but pain is not always controlled by NSAIDs alone and patients are not always hospitalized for treatment such as analgesic infusions. Local anesthetics administered preoperatively can be beneficial during the immediate postoperative period; however, maximum duration averages 2 to 8 hours.3 The exception to this is with liposomal bupivacaine (ie, liposome-encapsulated bupivacaine), which is FDA approved for use in both dogs4 and cats5 for ≤72 hours of analgesia. This drug can be used for a myriad of anesthetic blocks6 but has been underused, likely due to cost and the label limitation to discard any unused drug within 4 hours of vial puncturing, which increases drug waste and limits the ability to share drug cost among patients.
In the present study, the authors addressed 2 key concerns regarding the ability to extend the use of a punctured vial of liposomal bupivacaine: whether sterility is maintained and whether the liposomes degrade and release free (ie, unencapsulated) bupivacaine. Vials of liposomal bupivacaine (20 mL) were stored at room temperature (75°F [24°C]) or refrigerated (41°F [5°C]) and punctured for aliquot withdrawal each day for 5 days.
No bacterial or fungal growth occurred from any sample, except for a control vial that grew Aspergillus spp, a common environmental fungal contaminant; this vial was only punctured on the last day of sampling. The liposomes gradually degraded and released free bupivacaine, but the level was only significant on day 5, which led the authors to conclude that single-use liposomal bupivacaine handled aseptically could be used extra-label in a multidose manner for ≤4 days.
Refrigeration caused more rapid liposomal degradation, but even with degradation, the free bupivacaine in both groups remained below recommended dosages. Thus, overdose under these circumstances would not occur, but free bupivacaine would not provide 72 hours of analgesia.