Lidocaine

Common indications

1. Very commonly, as a first choice local anaesthetic in, for example, urinary catheterisation and minor procedures (e.g. suturing).
2. Uncommonly, as an antiarrhythmic drug in ventricular tachycardia (VT) and ventricular fibrillation (VF) refractory to electrical cardioversion (although amiodarone is preferred for the latter indication).

 

Mechanisms of action

• Lidocaine (formerly known as lignocaine) enters cells in its uncharged form, then accepts a proton to become positively charged. From inside the cell, it enters and then blocks voltage-gated sodium channels on the surface membrane. 
• This prevents initiation and propagation of action potentials in nerves and muscle, inducing local anaesthesia in the area supplied by blocked nerve fibres. In the heart, it reduces the duration of the action potential, slows conduction velocity and increases the refractory period. These effects may terminate VT and improve the chances of successfully treating VF.

 

Important adverse effects

• The most common side effect is an initial stinging sensation during local administration. 
• Systemic adverse effects are, predictably, more likely after systemic administration, whether intentional (as when it is used as an antiarrhythmic) or inadvertent (due to accidental intravascular injection during local administration). 
• Its effects on the neurological system include drowsiness, restlessness, tremor and fits. 
• It generally causes relatively little cardiovascular toxicity, but in overdose it may cause hypotension and arrhythmias.

 

Warnings

• Used appropriately as a local anaesthetic, lidocaine is generally very safe. 
• It depends heavily on hepatic blood flow for its elimination. 
• Therefore, the dose should be reduced in states of reduced cardiac output.

 

Important interactions

• As the duration of action of local anaesthetics depends on how long they stay in contact with the neurones, co-administration with a vasoconstrictor (e.g. adrenaline [epinephrine]) produces a desirable interaction that may prolong the local anaesthetic effect.