Miller RJ, et al. - In this prospective, observational study, researchers studied the pharmacokinetics of ropivacaine in patients undergoing elective total knee arthroplasty with local infiltration analgesia as the primary analgesic method. Additionally, plasma ropivacaine concentrations were measured over the first 24 hours postoperatively in order to determine the incidence of biochemical toxicity. In all patients, the peak total ropivacaine concentration was found to be below quoted toxic concentrations (2.2 μg/mL). The occurrence of this peak was later than has previously been described in those undergoing neuraxial or peripheral nerve block, occurring between 6 and 24 hours. When planning local infiltration analgesia, the impact of age, weight, and renal function on systemic ropivacaine concentration was recommended to be taken into account. Female sex was identified as a factor with no previously established relation to peak ropivacaine concentrations.