Class B Lidocaine/Mexiletine/Phenytoin Mode of action Little effect on normal tissues Decreases Purkinje ERP/ automaticity Increases ventricular fibrillation threshold Depresses conduction, esp at high rates (Mexiletine) Suppresses dig-induced delayed afterdepolarizations (Phenytoin) ECG changes Slight V QTc(Lidocaine/Phenytoin
Class IB Lidocaine/Mexiletine/Phenytoin • Mode of action – Little effect on normal tissues – Decreases Purkinje ERP/ automaticity – Increases Ventricular fibrillation threshold – Depresses conduction, esp. at high rates (Mexiletine) – Suppresses dig-induced delayed afterdepolarizations (Phenytoin) • ECG changes – Slight QTc (Lidocaine/Phenytoin)
Class B Lidocaine Use: VT(acute) Acts rapidly; no depression of contractility/AV conduction Kinetics t112: 5-10 min(1st phase); 80-110 min(2nd phase) Drug interactions Decreased metabolism w/ CHF/hepatic failure propranolol, cimetidine Increased metabolism w/ isuprel, phenobarbital phenytoin
Class IB Lidocaine • Use: VT (acute) – Acts rapidly; no depression of contractility/AV conduction • Kinetics – t1/2 : 5-10 min (1st phase); 80-110 min (2nd phase) • Drug interactions – Decreased metabolism w/ CHF/hepatic failure, propranolol, cimetidine – Increased metabolism w/ isuprel, phenobarbital, phenytoin