Pharmacokinetics and Pharmacodynamics of Ropivacaine 2 mg/mL, 5 mg/mL, or 7.5 mg/mL After Ilioinguinal Blockade for Inguinal Hernia Repair in Adults

The aim of our study was to evaluate the pharmacokinetics and pharmacodynamics of ropivacaine in ilioinguinal-iliohypogastric blocks (IIB). After ethics committee approval and informed consent, 80 male adults scheduled for inguinal hernia repair were enrolled and randomized into four groups. After induction of general anesthesia, an IIB was performed double blinded in Groups 1, 2, and 3 with 0.25 mL/kg ropivacaine 2 mg/mL, 5 mg/mL, or 7.5 mg/mL and with saline in the Control group. Plasma concentration of ropivacaine was determined in venous blood using reversed-phase high-performance liquid chromatography. IIB with ropivacaine resulted in peak plasma concentrations of 0.3 ± 0.15 μg/mL (Group 1) (mean ± SD), 0.75 ± 0.45 μg/mL (Group 2), or 1.57 ± 0.82 μg/mL (Group 3). These concentrations occurred after 30 (15–60) min, median (range), 30 (10–60) min, and 45 (15–60) min, in the respective groups. Three of 19 patients in Group 1, 6 of 18 in Group 2, and 5 of 20 in Group 3 did not need any additional analgesics within 24 h postoperatively, but all 20 control patients did. Time to the first demand for analgesia was significantly shorter in the Control group (median 0.3 h [range 0–2.8]) compared with 1.5 h (0.5–24 h), 2 h (0.5–24 h), and 2 h (1.0–24 h) in Groups 1, 2, and 3, respectively. Three patients in Group 3 had a postoperative motor block of the femoral nerve. In conclusion, a ropivacaine dose of 0.25 mL/kg of 5 mg/mL seems adequate for IIB accompanying general anesthesia for postoperative pain relief. However, the pharmacokinetic results obtained suggest that even larger doses (0.25 mL/kg of 7.5 mg/mL ropivacaine) for IIB do not result in plasma concentrations in a toxic range. Implications Ropivacaine, a new local anesthetic, proved to be effective for pain relief after hernia repair in ilioinguinal blocks accompanying general anesthesia. Plasma concentrations peaked after 30–45 min, and were within safe limits after application of 0.25 mL/kg of 2, 5, or 7.5 mg/mL ropivacaine.