Observed and predicted accumulation of local anaesthetic agents during continuous extradural analgesia.

After lumbar extradural injections of ligocaine or etidocaine for surgical anaesthesia further accumulation in the plasma was minimal following top-up injections for pain relief after operation. The dose regimens were: 20 ml of 2% plain lignocaine HCl solution for surgical anaesthesia followed by 10 ml every 1 h until 4 h, and 20 ml of 1% plain etidocaine HCl solution for surgical anaesthesia followed by 10 ml every 2 h until 8 h. Plasma drug concentrations measured after initial doses were used to predict those following successive doses. Agreement between predicted and experimental values was good and further projections were made concerning the local accumulation of etidocaine.