The effects of adding adrenaline to etidocaine and lignocaine in extradural anaesthesia II: Pharmacokinetics.

The addition of adrenaline to solutions of etidocaine or lignocaine for extradural administration resulted in significantly lower plasma koncentrations in both the arterial blood (14% decrease for etidocaine and 43% decrease for lignocaine) and venous blood (35% and 60% decreases for etidocaine and lignocaine respectively). The nett absorption over the first 4 h after administration, measured from the area under the plasma concentration-time curve, was decreased by the addition of adrenaline (18% and 30% decreases for etidocaine and lignocaine respectively). Both drugs were absorbed in a biexponential manner, having similar fast absorption rates but with etidocaine having a longer absorption half-life in the slow absorption phase. It is concluded that the addition of adrenaline reduces the fraction of the dose being absorbed during the first (fast) phase rather than influencing the absorption rate constants.