An Observational Study of the Pharmacokinetics of Adductor Canal Block using Liposomal Bupivacaine and Standard Bupivacaine in Total Knee Arthroplasty

Abstract Background Periarticular local infiltration of analgesia (LIA) and regional nerve block using adductor canal block (ACB) have been effective in managing postoperative pain for total knee arthroplasty (TKA). It has been shown that combining ACB with LIA can significantly reduce pain scores and morphine consumption compared with LIA alone. However, this raises concerns about the potential risk of local anesthetic systemic toxicity (LAST), especially with the large doses of total local anesthetic used in both LIA and ACB. This study was to evaluate the plasma level of bupivacaine over a 72-hour period following ACB using 66.5 mg of liposomal bupivacaine (LB) in patients undergoing TKA with LIA using 300 mg ropivacaine. Methods This was a prospective observational study. Ten patients undergoing primary, unilateral, simple revision TKA in a tertiary hospital in Hong Kong between December 2020 to February 2022 were included in the study. The primary outcomes were the time to peak plasma concentration (Tmax) of bupivacaine and the peak plasma concentration (Cmax) of bupivacaine. The secondary outcome was the presence of LAST. Results Tmax of bupivacaine was 48 hours while Cmax of bupivacaine was 88 mcg/L, this value was far below 2000 mcg/L, the defined toxic plasma concentration of bupivacaine. Conclusions There is still room for increasing the dose of LB used in ACB for TKA patients, further dose-defining studies with PK data are needed to define the optimal dose that would balance the safety and efficacy of LB. Trial registration The clinical trial was registered at ClinicalTrials.gov with registration number NCT04916392.