The effect of lipid emulsion on pharmacokinetics and tissue distribution of bupivacaine in rats.

While lipid emulsion may reverse the systemic toxicity of bupivacaine, the pharmacokinetics and tissue distribution of bupivacaine after lipid emulsion infusion are not clear. In this study, we assessed the influence of lipid emulsion administration on the pharmacokinetics and tissue distribution of bupivacaine. Rats in the lipid group were administered IV bupivacaine at the rate of 2 mg·kg(-1)·min(-1) for 4 minutes, and then were treated with an infusion of 30% lipid emulsion at the rate of 3 mL·kg(-1)·min(-1) for 5 minutes; saline was substituted in the control group (n = 6 for pharmacokinetics). We then randomly assigned 100 rats into the lipid group and control group (n = 50 for distribution). The toxicity model and treatment were the same as the pharmacokinetic portion. Plasma and tissues including brain, heart, liver, spleen, lung, kidney, omentum, and muscle were collected. The plasma concentration and tissue content of bupivacaine were measured by a liquid chromatography-tandem mass spectrometric method. A 2-compartmental analysis was performed to calculate the pharmacokinetics of bupivacaine. All data are shown as mean ± SD. After treatment with the lipid emulsion, t1/2β of bupivacaine in the lipid group was significantly shorter (110 ± 25 minutes vs 199 ± 38 minutes, P = 0.001), the clearance was higher (14 ± 4 mL·mg(-1)·kg(-1) vs 9 ± 4 mL·mg(-1)·kg(-1), P = 0.038), and the t1/2α was longer than that of the control group (4 ± 1 minutes vs 2 ± 1 minutes, P = 0.014); the K12 in the lipid group was less than that of the control group (0.13 ± 0.04 vs 0.32 ± 0.13, P = 0.011). In the lipid group, the bupivacaine content in heart, brain, lung, kidney, and spleen was lower than that in the control group, but higher in the liver at 20, 30, and 45 minutes. The lipid sink phenomenon was observed in this study. The use of a lipid emulsion accelerated the elimination of bupivacaine.