Effect of bupivacaine concentration and formulation on canine chondrocyte viability in vitro

Abstract

Objective: To quantitate bupivacaine concentration and formulation effects on chondrocyte viability in vitro.

Study design: Controlled laboratory study.

Sample population: Primary canine chondrocyte isolates.

Methods: Cell passage 3 and 4 canine chondrocytes were exposed to 0.9% saline; canine chondrocyte growth medium; 0.4, 0.5, 0.6, 1.5, 2.5, 3.5, or 5 mg/mL preservative-free standard formulation bupivacaine (SFB); or 13.3 or 6.65 mg/mL liposomal encapsulated bupivacaine (LEB) for 1 hour. Chondrocyte viability and clonogenicity were quantitated with 3-(4,5-dimethylthiazol-2-31 yl)-2,5-diphenyltetrazolium bromide (MTT) and clonogenic assays, respectively. Differences among concentrations and formulations were assessed with Kruskal-Wallis and Dwass-Steel-Critchlow-Fligner post hoc tests.

Results: Growth medium had the highest cell viability based on MTT metabolism. Similarly, all LEB concentration groups had higher cell viability compared with SFB concentration cells treated with 3.5 or 5 mg/mL SFB (P < .03). Among SFB concentrations, cell viability was higher at 0.6 mg/mL compared with at 2.5 mg/mL or greater (P < .03). Cell clonogenicity was not significantly different between saline, culture medium, or 0.5 mg/mL SFB. Clonogenicity was lower with all tested LEB concentrations compared with saline or medium (P < .02).

Conclusion: In vitro toxicity of SFB on canine chondrocytes is concentration dependent. Liposomal encapsulated bupivacaine may have time-dependent effects resulting in chondrotoxicity.

Clinical significance: Clinically relevant concentrations of SFB after a single injection may not result in chondrotoxic effects in vitro. Liposomal encapsulated bupivacaine should not be used in the articular environment.