[Pharmacokinetics of anti-arrhythmics. 2. Clinical applications]

The clinical usage of antiarrhythmic drugs may pose problems which could be solved by the direct application of the basic principles of pharmacokinetics. These problems involve the calculation of intravenous infusion rates and or oral dosages. Examples are provided by the rate of initial infusion of lignocaine in order to obtain a concentration within the therapeutic range, the eventual adjustment of this rate of infusion and the calculation of a loading dose. As regards the oral route, the calculation of the doses of procainamide is taken as an example. The estimation of the serum procainamide is a method for determining whether the dose should be increased or whether the drug is ineffective when no clinical result is observed. The pharmacokinetics of the main antiarrhythmic drugs are reviewed; procainamide, quinidine, propanolol, phenytoin, disopyramide. The therapeutic dose, clearance, extraction coefficient, bioavailability and half-life are the object of particular study. The fractioning of the dose and the total dose in a 24 hour period depend on these factors. The effects of cardiac, renal and hepatic failure on the clearance of each drug are recalled. These pharmacokinetic principles help the clinician not only in the prescription of an antiarrhythmic drug but also in deciding on the indications for drug serum concentration, estimations which are particularly useful in some difficult clinical situations, and in interpreting the results.