Prilocaine pharmacokinetics and the influence of vitamin C on methaemoglobin concentrations in tumescent anaesthesia

Abstract

SummaryIn tumescent local anesthesia high doses of prilocaine are used but valid data on the pharmacokinetics and metabolism of prilocaine during this technique of anesthesia are rare. Patients, methods: In this study plasma prilocaine and methaemoglobin concentrations were measured after subcutaneous injection of prilocaine at doses of 6.69 to 19.21 mg/kg in one hundred patients undergoing varicose vein surgery under tumescent local anesthesia. Half of the patients were randomised to intravenous treatment with 2000 mg ascorbic acid. Glucose-6-phosphate dehydrogenase activity was measured preoperatively. Results: Maximum plasma prilocaine concentrations ranged between 0.14 and 0.86 μg/ml and thus remained below the toxic threshold. Methaemoglobin concentrations ranged between 0.4 and 16.9%. There was no significant effect of vitamin C on the methaemoglobin concentration. Glucose-6-phosphate dehydrogenase activity and methaemoglobin concentrations did not correlate. Conclusions: Tumescent anesthesia with prilocaine at a maximum dose of 20 mg/kg body weight is a safe procedure in varicose vein surgery although the risk of methaemoglobinemia is not reduced by using vitamin C.