Time to onset of analgesia following local infiltration of liposome bupivacaine in healthy volunteers: A randomized, single-blind, sequential cohort, crossover study

Background/Objective: Bupivacaine liposome injectable suspension is a novel, prolonged-release formulation of bupivacaine. The time to onset of analgesia following an injection of liposome bupivacaine compared with placebo (normal saline) was investigated using a novel incisional pain model. Bupivacaine HC1 was used as a positive control, compared with placebo to verify the validity of the study. Materials and methods: In this Phase 1, single-blind, crossover study, healthy volunteers (n = 132) were randomized to four sequential cohorts to receive subcutaneous normal saline in one arm and either liposome bupivacaine 40 mg or bupivacaine HC1 7.5 mg in the other. At 30, 15, 5, and 2 minutes after study drug administration for Cohorts 1 - 4 respectively, an incision was made in each arm and 18% acetic acid solution was applied to elicit pain. The primary outcome measure was a subject's assessment of pain intensity on a 100 mm visual analog scale. Results: Statistically significant differences in pain intensity scores between liposome bupivacaine and normal saline were observed at 30, 15, 5, and 2 minutes postdose; similar findings were reported for bupivacaine HC1 vs. normal saline. Both liposome bupivacaine and bupivacaine HC1 were well tolerated and achieved > 30% pain reduction, normalized to placebo, within 5 minutes. Conclusions: These results indicate that liposome bupivacaine offers time to onset characteristics similar to traditional bupivacaine HC1: clinically meaningful analgesia within 2 minutes after administration and substantial analgesia by 5 minutes.