The clinical pharmacology of lidocaine congeners--review of encainide, flecainide, lorcainide and tocainide.

Among the newer antiarrhythmic drugs currently being evaluated are the four so-called lidocaine congeners, encainide, flecainide, lorcainide and tocainide. A knowledge of the pharmacokinetic properties of these agents may help to distinguish between them and may also be important for rational patient prescribing. Encainide and lorcainide both undergo predominantly hepatic elimination: both appear to form metabolites which have antiarrhythmic activity of their own and which have longer elimination half-lives than the parent compounds, resulting in accumulation with chronic administration. Flecainide and tocainide are cleared mainly by the kidneys, do not have active metabolites and have long elimination half-lives. All of the drugs have significant antiarrhythmic activity and this is proportionate to the plasma concentration of either the drug alone or combined with the active metabolites. Comparative effectiveness between the drugs has not been established. In general, all four drugs have only minor adverse effects, principally gastrointestinal or neurological, which may disappear with small dose reductions. However, cardiac effects can also occur and rarely pro-arrhythmic effects have been described, particularly with encainide and flecainide. All four drugs are suitable for long-term administration on a twice-daily basis.