Ventricular arrhythmias intravenous drug dose

This is a class IB drug used primarily for the emergency treatment of ventricular arrhythmias. It has little effect on sinus node automaticity but depresses normal and abnormal forms of automaticity in Purkinje fibres. It is generally ineffective against supraventricular and accessory pathway-induced (e.g. WPW syndrome) arrhythmias. Lidocaine is relatively safe and free from adverse cardiovascular side effects. It causes minimal cardiodepression, although high doses can cause heart block. The most common side effect is a dose-related CNS toxicity. It is given intravenously as a bolus of 1 mg-kg-1 followed by an infusion of 20-50 pg-kg-l-min-1. 

A man with sustained ventricular tachycardia taking high-dose intravenous procainamide 2 g every 8 hours had a 70% increase in his steady-state plasma procainamide levels, from 9.1 to 15.4 nanograms/mL, when he also took quinidine gluconate 324 mg every 8 hours. The procainamide half-life increased from 3.7 to 7.2 hours and its clearance fell from 27 to 16 L/hour. His QTc interval increased from 648 to 678 milliseconds. In another study in patients with ventricular arrhythmias, quinidine was combined with procainamide. The doses were adjusted based in part on the QT interval. The QTc interval was longer with the combination (499 milliseconds) than each drug alone (quinidine 470 milliseconds, procainamide 460 milliseconds) despite using reduced doses in the combination (mean quinidine dose reduced by 28% mean procainamide dose reduced by 32%) ... 

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