LIGNOCAINE

1) Action

• Membrane stabilising agent [local anaesthetic & antiarrhythmic]

• Class IB antiarrhythmic of amide type

2) Mechanism

• Stabilises neuronal membrane & prevents the initiation & transmission of nerve impulses

• Antiarrhythmic effect by increasing the electrical stimulation threshold of the ventricle during diastole

• Depresses slow spontaneous depolarisation [phase 4] ie decreases automaticity

• Increases effective refractory period

• Potent suppressor of abnormal cardiac activity

• Blocks both activated & inactivated sodium channels

• Suppresses activity of depolarised, arrhythmogenic tissues while minimally interfering with the electrical activity of normal tissues: therefore is effective in suppressing arrhythmias associated with depolarisation [eg ischaemia, digitalis toxicity] but is relatively ineffective against arrhythmias occurring in normally polarised cells [eg AF & Af]

3) Indications

• Local anaesthetic

• Management of arrhythmias: eg post MI, digitalis toxicity, post cardiac arrest

• Major indication is suppression of VT and prevention of VF after MI: is first choice agent

4) Effects on organs—side effects

• Mild hypotension

• Convulsions

• Bradycardia

5) Toxic effects/ precautions with administration

• Least toxic of currently used antiarrhythmic drugs

• Proarrhythmic in < 10% of patients [good record]

• In large doses may cause hypotension partly by reducing contractility

• Lower doses in renal/liver failure

6) Contraindications

• Heart blocks

• Is rarely effective in supraventricular arrhythmias except WPW syndromes

• Severe heart failure

8) Loading dose, maintenance dose, frequency & method of administration

100 mg/5 ml

• Must be given IV

• bolus 1mg/kg of 2% 5 ml ampoule over 1 — 2 min, lasts 15 — 20 min; repeated once or twice after 10 — 20 min

• Infusion follows bolus to maintain therapeutic levels

9) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Elimination half life: 100 min

• % plasma protein binding: 51%