Paper I
Question
Mechanism of action of lignocaine
Answer
Lignocaine (lidocaine) is an amide local anaesthetic. It blocks voltage-gated sodium channels on the inner surface of the neuronal membrane, preventing sodium influx and thereby preventing depolarization and propagation of the nerve action potential — producing reversible loss of sensation in the area supplied by the nerve. It acts preferentially on smaller, unmyelinated fibres (pain, temperature) before larger myelinated fibres. (As an antiarrhythmic, it blocks cardiac sodium channels similarly, suppressing abnormal ventricular automaticity.)