Objective To determine whether bupivacaine liposomal injectable suspension (BLIS) supports microbial growth when artificially inoculated and to evaluate liposomal stability in the face of this extrinsic contamination as evidenced by changes in free bupivacaine concentrations. Study design A randomized, prospective in vitro study in which three vials of each BLIS, bupivacaine 0.5%, and propofol were individually inoculated with known concentrations of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans (n = 36) to quantify bacterial and fungal growth was conducted. Over 120 hours, aliquots from contaminated vials were withdrawn, plated, and incubated to determine microbial concentrations. High-pressure liquid chromatography (HPLC) was used to evaluate free bupivacaine concentrations over time in BLIS. Data were analyzed using a mixed effects model with multiple comparisons. Sample population Twelve vials of each BLIS, bupivacaine 0.5%, and propofol. Results BLIS did not support significant growth of Staphylococcus aureus or Candida albicans at any time. BLIS supported significant growth of Escherichia coli and Pseudomonas aeruginosa beginning at the 24 hour time point. Bupivacaine 0.5% did not support significant growth of any organisms. Propofol supported significant growth of all organisms. Free bupivacaine concentrations changed minimally over time. Conclusion Bacterial and fungal contaminant growth in artificially inoculated BLIS is organism dependent. BLIS supports significant growth of Escherichia coli and Pseudomonas aeruginosa. Extra-label handling of BLIS should only be undertaken with caution and with adherence to strict aseptic technique.