Xylocaine Pump Spray Mechanism of Action

Pharmacotherapeutic Group: Local anaesthetic. ATC Code: N01BB02.
Pharmacology: Xylocaine Pump Spray is intended for use on mucous membranes and provides an efficient surface anaesthesia, which lasts for approximately 10-15 min. The anaesthesia usually occurs within 1-5 min depending on the area of application.
Pharmacokinetics: The extent of absorption of lidocaine is dependent upon the total dose administred, and also upon the specific site of application and the duration of exposure. In general, the rate of absorption following topical administration is most rapid after intratracheal and bronchial administration. Such applications may therefore result in rapidly rising plasma concentrations, with an increased risk of toxic symptoms eg, convulsions. Lidocaine is well-absorbed from the gastrointestinal tract, but undergoes extensive first-pass metabolism.
The plasma protein-binding is predominant to α-1-glycoprotein.
The main elimination pathway of lidocaine is by liver metabolism. De-alkylation to monoethylglycine xylidide (MEGX) is mediated mainly by cytochrome P-450 3A4. MEGX is metabolised to 2,6-xylidine and glycine xylidide (GX). 2,6-xylidine is metabolised further by CYP2A6 to 4-hydroxy-2,6-xylidine, which is the major metabolite in the urine (80%) and is excreted as conjugate. MEGX has a convulsant activity equivalent to that of lidocaine, while GX is devoid to convulsant activity. MEGX appears to occur in similar plasma concentration as the parent substance. The elimination half-life of lidocaine and MEGX following an IV bolus dose are approximately 1.5 hrs and 2.5 hrs, respectively.
On the account of the rapid hepatic metabolism, the kinetics are sensitive to all alterations in liver function. The half-life can be more than doubled with impaired liver function. Impaired renal function dose not affect the kinetics, but can increase the accumulation of metabolites.
Factors such as acidosis and the use of central nervous system stimulants and depressants affect the levels of lidocaine required to produce systemic effects. With plasma levels from 5-10 mg/mL, signs of overdosage become apparent.