Efficacy and uptake of ropivacaine and bupivacaine after single intra-articular injection in the knee joint

The efficacy of ropivacaine 100 mg (5 mg ml(-1)), 150 mg (7.5 mg ml(-1)) and 200 mg (10 mg ml(-1)) and bupivacaine 100 mg (5 mg ml-1) given by intra-articular injection into the knee after the end of surgery was studied in 72 ASA I-II patients scheduled for elective knee arthroscopy under general anaesthesia in a randomized, double-blind study. Kapake (paracetamol 1 g and codeine 60 mg) was given as a supplementary analgesic. Pain scores were assessed 1-4 h after surgery and a verbal rating scale of overall pain severity was assessed on second postoperative day. Ropivacaine or bupivacaine concentrations were determined in peripheral venous plasma up to 3 h after injection in eight patients in each group. Verbal rating pain scores were lower with ropivacaine 150 mg compared with bupivacaine 100 mg (P <0.05). There was a tendency for lower analgesic consumption and pain scores with all doses of ropivacaine (not significant). The mean (SID) maximum total plasma concentrations of ropivacaine were 0.64 (0.25), 0.78 (0.43), and 1.29 (0.46) mg litre(-1) after 100, 150 and 200 mg. The corresponding unbound concentrations were 0.018 (0.009), 0.024 (0.020) and 0.047 (0.022) mg litre(-1). Both were proportional to the dose. The maximum total concentration after bupivacaine 100 mg was 0.57 (0.36) mg litre(-1). The time to reach maximum plasma concentration was similar for all doses and varied between 20 and 180 min. All concentrations were well below the threshold for systemic toxicity.