Blood concentration of lignocaine after application of 2% lignocaine gel in the urethra.

In 35 patients undergoing topical anaesthesia with lignocaine (lidocaine) gel (2% Xylocaine gel) the concentration of lignocaine base was measured in repeated venous blood samples. Twenty patients (group I) were given 20 ml of 2% lignocaine gel (400 mg lignocaine) and 5 patients (group II) received 40 ml (800 mg lignocaine) endourethrally. These 2 groups of patients underwent either dilation of the urethra or urethrocystoscopy. Ten patients (group III) undergoing transurethral resection of the prostate or a bladder tumour, were given 20 ml of gel (400 mg lignocaine) plus spinal anaesthesia with 2 ml of 5% lignocaine (100 mg lignocaine) with 7.5% glucose (Xylocaine "heavy"). The mean peak blood concentrations of lignocaine in these 3 groups were 0.06, 0.15 and 0.36 micrograms/ml respectively. Patients undergoing urethral dilatation had significantly higher blood concentrations than cystoscopy patients. The blood concentrations in group III were not higher than the expected value when spinal anaesthesia and lignocaine gel were given simultaneously. There was no statistically significant difference in the blood concentration between patients undergoing different types of transurethral resection (prostate and cancer of the bladder). Lignocaine applied endourethrally gives an extremely low blood concentration which is far below the level which can cause general toxic symptoms.