Pharmacokinetics of ropivacaine following caudal analgesia in children

Ropivacaine has a favourable toxicity profile for epidural anaesthesia in a dults, so it may also be an appropriate agent for epidural analgesia in chi ldren. We therefore designed this study to determine the pharmacokinetic va riables of ropivacaine relevant to the risk of toxicity, after caudal admin istration in children. We studied nine healthy children, aged 1-6 years who received 1 ml.kg(-1) of ropivacaine 0.25% for caudal analgesia. Venous blo od samples were collected at intervals for 12 h after injection. Total plas ma concentration of ropivacaine was assayed by high performance liquid chro matography, and pharmacokinetic descriptors were estimated from the plasma concentration-time data. The median peak venous plasma concentration was 79 9 mu g.l(-1) [interquartile range (IQR) 707-1044 mu g.l(-1)], and was reach ed at a median time of 1.5 h (IQR 0.5-2 h). The mean elimination half-life was 3.9 h (95% CI 2.7-5.0 h), and the mean apparent clearance and volume of distribution were 7.6 +/- 1.6 ml.min(-1).kg(-1) (95% CI 6.1-9.1 ml.min(-1) .kg(-1)) and 2.4 +/- 0.6 l.kg(-1) (95% CI 1.9-3.0 l.kg(-1)), respectively. Analgesia was satisfactory in all cases and no systemic ropivacaine toxicit y was observed. Caudal administration of weight-adjusted doses of ropivacai ne to children resulted in systemic exposure similar to that reported for a dults. No systemic toxicity was observed. The findings strengthen predictio ns that the relative systemic safety of epidural ropivacaine in adults will apply to children. However, the pharmacokinetics and safety of epidural ro pivacaine need to be studied further in children with circumstances that af fect drug disposition and systemic tolerance.