Factors affecting plasma levels of lignocaine and prilocaine.

Plasma levels of local anaesthetics following their injection are affected by many factors. Serial plasma levels following injection of lignocaine and prilocaine at various rates in over 500 patients have been measured and this has allowed some of these factors to be assessed and quantified. The vascularity of the site of injection causes major differences in the maximum plasma level. Prilocaine consistently gives lower levels than lignocaine. Adrenaline causes a reduction in the plasma levels of both drugs and the optimal concentration is 1:200,000. Speed of injection is important when giving the drugs intravenously but not epidurally. The concentration of the injected solution does not affect the plasma levels. The weight and age of the patients (all adult females) were unrelated to the mayi'mnm plasma levels.