Impact of epinephrine on ropivacaine pharmacokinetics in TAP blocks: a randomized controlled trial.

Background: Ropivacaine is commonly used in abdominal wall blocks due to its safety profile, and the addition of epinephrine is hypothesized to prolong analgesic duration and reduce systemic absorption. However, previous studies have been limited by non-weight-adjusted dosing and potential pharmacokinetic interactions, and inadequate investigation of the free form of ropivacaine.

Objective: To characterize and compare the pharmacokinetics of total and free ropivacaine administered at a weight-adjusted dose of 1 mg/kg in Transversus Abdominis Plane (TAP) blocks, with and without epinephrine (1:200 000; 5 µg/mL).

Methods: In this randomized controlled trial, 40 patients undergoing laparoscopic colectomy received bilateral TAP blocks with ropivacaine alone (TAP/E-) or ropivacaine with epinephrine (TAP/E+). Pharmacokinetic parameters, including maximum plasma concentration (Cmax), time to Cmax (Tmax), and area under the concentration-time curve, were assessed over 240 min. Secondary outcomes included α₁-acid glycoprotein (AGP), analgesia, safety, and mean plasma concentration (Cmean).

Results: The mean Cmax in the TAP/E+ group (0.531±0.245 µg/mL) was not significantly different from that in the TAP/E- group (0.746±0.428 µg/mL). Epinephrine significantly prolonged Tmax (165 vs 55.9 min in TAP/E-, p<0.001) and reduced Cmean (p=0.005). No serious adverse events occurred, though QT interval prolongation was observed in both groups.

Conclusion: This study demonstrates that adding epinephrine did not alter the Cmax of ropivacaine in TAP blocks, but did prolong the time to reach Cmax. These findings support the routine inclusion of epinephrine in TAP blocks and provide a basis for multimodal analgesia strategies.

Trial registration number: NCT04959123.