Lidocaine Intravenous

Lidocaine given intravenously is a class IB antiarrhythmic used for ventricular tachycardia and ventricular fibrillation when amiodarone is not available, especially after a myocardial infarction or in digoxin toxicity. It acts mainly in diseased or ischaemic tissue and has little effect on atrial rhythm. It is cheap and available in most East African hospitals, but it is not a first line drug in cardiac arrest.

Classification. Class IB antiarrhythmic (sodium channel blocker); amide local anaesthetic.

Mechanism. Blocks inactivated fast sodium channels, shortening the action potential and refractory period in ventricular tissue, and slowing conduction in depolarised (ischaemic) cells. It has little effect on the sinus node or atrioventricular conduction at usual doses.

Pharmacodynamics. IV onset within 1 to 2 minutes, duration 10 to 20 minutes after a bolus. Little effect on the ECG intervals. Raises the defibrillation threshold slightly.

Pharmacokinetics. Not given orally (high first pass metabolism). Distribution half life 8 minutes; elimination half life 1.5 to 2 hours (longer, up to 10 hours, in heart failure, liver disease, older adults and after prolonged infusions). Metabolised by CYP1A2 and CYP3A4 to active metabolites (monoethylglycinexylidide); 10% excreted unchanged. Therapeutic level 1.5 to 5 mg/L.

Ventricular tachycardia or ventricular fibrillation (refractory), adult.

• Loading: 1 to 1.5 mg/kg (50 to 100 mg) IV bolus over 2 minutes.

• Repeat 0.5 to 0.75 mg/kg every 5 to 10 minutes if needed; maximum total 3 mg/kg.

• Maintenance infusion 1 to 4 mg/minute (15 to 50 micrograms/kg/minute) for up to 24 hours; reduce by half in heart failure, liver disease, shock or in older adults.

Cardiac arrest with ventricular fibrillation or pulseless ventricular tachycardia, adult. 1 to 1.5 mg/kg IV or intraosseous after the third shock and adrenaline when amiodarone is not available, then 0.5 to 0.75 mg/kg; maximum 3 mg/kg.

Children. 1 mg/kg IV bolus (maximum 100 mg); infusion 20 to 50 micrograms/kg/minute (maximum 3 mg/kg total bolus). Use under specialist supervision.

Contraindications. Heart block (second or third degree) without a pacemaker; severe sinoatrial disorder; Adams Stokes syndrome; hypersensitivity to amide local anaesthetics; severe hepatic impairment (dose reduction required); porphyria.

Warnings. Toxicity: perioral numbness, tinnitus, metallic taste, dizziness, confusion, slurred speech, muscle twitching, seizures, coma, bradycardia and cardiac arrest (levels above 5 mg/L). Local anaesthetic systemic toxicity needs immediate lipid emulsion. Do not use preparations containing adrenaline. Heart failure, shock, low cardiac output and liver disease reduce clearance. Risk of asystole after sudden bradycardia.

Adverse effects. Light headedness, paraesthesia, drowsiness, confusion, tremor, seizures, hypotension, bradycardia, heart block, rarely anaphylaxis.

Interactions. Beta blockers (propranolol, metoprolol) and cimetidine: raised levels. Amiodarone, phenytoin: additive cardiac depression and seizures. CYP1A2 inhibitors (ciprofloxacin, fluvoxamine) and CYP3A4 inhibitors (erythromycin, azoles): raised levels. Other antiarrhythmics: additive effects. Suxamethonium: prolonged action.

Treatment of toxicity. Stop the infusion; give oxygen and support the airway; treat seizures with a benzodiazepine; for cardiac arrest or severe toxicity, give 20% lipid emulsion 1.5 mL/kg IV bolus over 1 minute, then infusion 15 mL/kg/hour; continue for 10 minutes after circulation is restored.

Special groups.

• Pregnancy: safe for arrhythmia treatment when needed; monitor foetal heart rate.

• Breastfeeding: small amounts in milk; compatible.

• Patients of African ancestry: no dose change.

• Older adults: halve the loading and infusion dose.

• Kidney impairment: no change for the first doses; metabolites accumulate in prolonged use.

• Liver impairment: halve the infusion rate; avoid in severe disease.

Formulations. Injection 1% (10 mg/mL) and 2% (20 mg/mL) plain, without adrenaline (cardiac syringes 100 mg in 5 mL); premixed infusion in 5% glucose 2 mg/mL.

Administration. IV through a secure line; bolus over 2 minutes; infusion by pump. Use plain lidocaine only.

Baseline. ECG, blood pressure, hepatic and cardiac function, potassium and magnesium.

Monitoring. Continuous ECG and blood pressure. Neurological symptoms (numbness, tinnitus, confusion). Plasma level after 12 to 24 hours of infusion, or earlier in heart failure, liver disease or older adults. Stop within 24 hours.

Stopping. Stop the infusion once rhythm is controlled or after 24 hours; the effect fades within 20 minutes.

Common prescribing errors. Using a preparation with adrenaline; giving a rapid large bolus; continuing the infusion beyond 24 hours; failing to halve the dose in heart failure or liver disease; confusing antiarrhythmic dosing with local anaesthetic dosing.