Blood Concentration of Lignocaine after Application of 2% Lignocaine Gel in the Urethra

Abstract

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.

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“…7 However, topical lidocaine is absorbed slowly and incompletely. 7 Previous reports 8,9 suggest that lidocaine is maximally absorbed at 15-60 minutes. In the present study, lidocaine gel was maintained in the urethra for a minimum of 15 minutes.…”

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“…The diverse efficacy of lidocaine gel may be because the absorption of topical lidocaine is slow and incomplete. Several groups have demonstrated that maximal lidocaine absorption requires 15 to 60 minutes [5, 12]. …”

Flexible cystoscopy in men: is topical anaesthesia with lignocaine gel worthwhile?

“…Whilst reflecting current clinical practice, the volume and amount of lignocaine gel used in the present study (10 ml of 2% gel= 200 mg lignocaine) is below that recommended by some manufacturers. There can be no doubt that increasing the quantity of lignocaine instilled would increase drug uptake from the urethra [16]. The clinical efficacy of such a strategem has been examined in detail by Brekkan et d. [lo].…”