<prompt> All are true about lidocaine except:It acts on sodium channels in both active and inactive stateIt is most cardiotoxic local anestheticIt is given IV in cardiac arrhythmiasExtensive first pass metabolism  <response>: Ans. b. It is most cardiotoxic local anesthetic Ref: Katzung 11e p239LidocaineMOA: Blocks both activated and inactivated Na channels with rapid kineticsQ.Pharmacokinetics: Has extensive first pass hepatic metabolismQ, only 3 of orally administered lidocaine appears in the plasma.Most physicians administer IV lidocaine only to patients with arrhythmias.Lidocaine ToxicityLidocaine is the least cardiotoxicQ of currently used Na channel blocker.Other side effects are:Neurologic: Paraesthesia, tremorsLight headedness.Hearing disturbancesSlurred speechConvulsionsUses of LidocaineVentricular tachycardiaQPrevention of ventricular fibrillationQLocal AnestheticsAminoesters single iAminoamides double i Procaine Chlorprocaine Tetracaine Benzocaine Cocaine Esters are metabolized by pseudocholinesterase except cocaine which is metabolized by liver High incidence of allergic reactions which are because of para aminobenzoic acid Solutions are not stable Lignocaine Mepivacaine Prilocaine Bupivacaine Etidocaine Ropivacaine Amides are metabolized primarily in liver. Low incidence of allergic reactions Solutions are stable Not destroyed even by autoclavingLocal Anesthetics: Mechanism of actionLA blocks Na channel from insideQ of cell membrane and raises the threshold of channel openingQ.Resting nerve is resistant to block and blockage develop rapidly when the nerve is stimulated repeatedlyQ.High Ca2 conc, lessens the degree of block. 