Pharmacokinetics of 0.75% ropivacaine and 0.5% bupivacaine after ilioinguinal-iliohypogastric nerve block in children.

BACKGROUND Blockade of the ilioinguinal and iliohypogastric nerves is a useful procedure in paediatric patients undergoing inguinal surgery. Bupivacaine 2 mg kg-1 has been recommended for this block. We compared the plasma concentrations of ropivacaine and bupivacaine following an ilioinguinal-iliohypogastric block. METHODS Forty children scheduled for elective inguinal surgery were randomized to receive 2 mg kg-1 of either 0.75% ropivacaine or 0.5% bupivacaine. Surgical anaesthesia was maintained with mask inhalation of oxygen, nitrous oxide and sevoflurane. Venous blood samples were drawn at regular intervals for up to 2 h and plasma was separated. Total venous plasma concentrations were determined by gas chromatography. RESULTS The groups were similar with respect to age, weight and dose of local anaesthetic. The peak plasma concentration achieved was significantly higher in the bupivacaine group compared with the ropivacaine group (2.2 vs 1.2 micrograms ml-1, P = 0.025). The time to peak plasma concentration was significantly shorter in the bupivacaine group (24 vs 35 min, P = 0.024). The initial distribution half time of bupivacaine was significantly shorter (3.6 vs 6.5 min, P = 0.020) compared with that of ropivacaine. CONCLUSIONS Bupivacaine is more rapidly absorbed from the injection site and leads to higher plasma concentrations than ropivacaine.