Ans. c. 7 mg/kg (Ref: Morgan 4/e p270)Maximum dose of lignocaine with adrenaline for local blocks in ophthalmic surgeries is 7 mg/kg."Maximum safe dose of lignocaine with epinephrine is 500 mg or 7 mg/kg.Lignocaine (Lidocaine or Xylocaine)Most commonly used LA. It is amide linked local anaesthetic that can be used as surface anesthetic agent (i.e. through mucous membrane or skin)Q.Lignocaine: Characteristic FeaturesVaso-ineffective: Neither vasoconstrictor nor vasodilatorNo mydriasis and cycloplegiaPropranolol increases risk of toxicity by decreasing clearance.Contraindicated in malignant hyperpyrexia and in patients with history of convulsions.Dose related neurological effects is main toxicity.Mechanism of Action:Lignocaine blocks both open (active) and closed (inactivated) cardiac Na+ channelsQ.Lignocaine is a local anesthetic that also is useful in acute intravenous therapy of ventricular arrhythmias. It is not useful in atrial arrhythmias.Lidocaine decreases the automaticity by reducing the slope of phase 4 and altering the threshold for excitability.Lidocaine is the least cardiotoxicQ of currently used Na+ channel blocker.Pharmacokinetics:It is well absorbed but undergoes extensive though variable first pass hepatic metabolismQ (only ~3% orally administered drug appearing in plasma); thus oral use of the drug is inappropriate.Therapeutic plasma concentrations of lidocaine may be maintained by intermittent intra muscular injections, but the IV route is preferred.Concentration of Lignocaine5%4%0.5% (Usually <2%)* Spinal anesthesia (Between arachnoid and piamater in subarachnoid space)* Topical:- Pharynx- Eye* Epidural anesthesia LignocaineMaximum safe doseMaximum safe dose with Adrenaline4.5 mg/kg or 300 mgQ7 mg/kg or 500 mgQUses of Lignocaine:It is used to suppress ventricular tachycardia (VT) and prevent ventricular fibrillation (VF).Its efficacy in chronic ventricular arrhythmia is poor but it suppresses VT due to digitalis toxicity (because it does not worsen AV block). However, it is not routinely prophylacticallY used to prevent VF in all acute Ml patients because it may increase mortality.Side-Effects of LignocaineCNSCVSRespiratoryAllergic* Stimulation followed by depression* Restlessness* Vertigo* Tremor* Convulsions* Respiratory failure (due to medullary depression).* Bradycardia* Arrhythmia* Hypotension* Cardiac failure* Depress hypoxic drive (ventilator response to low PaO2)* Apnea due to phrenic or intercostal nerve paralysis or depression of respiratory centre.* IV lignocaine blocks reflex bronchoconstriction associated with intubation, whereas aerosol lignocaine may lead to bronchospasm* Bronchospasm* Urticaria* Angioedema