All are true about lidocaine except:
Ans. b. It is most cardiotoxic local anesthetic (Ref: Katzung 11/e p239)LidocaineMOA: 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 'i')Aminoamides (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 autoclaving)Local 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.
It acts on sodium channels in both active and inactive state
It is most cardiotoxic local anesthetic
It is given IV in cardiac arrhythmias
Extensive first pass metabolism
Miscellaneous (Local and Regional Anesthesia)