Transcainide(R 54718), a new lidocaine analog, is an orally active antiarrhythmic agent.Transcainide blocks the open state of BTX-activated sodium channels in bovine heart and rat skeletal muscle.

Transcainide (IC50=0.3 μM) inhibited equilibrium [3H]batrachotoxinin binding to sodium channels present on freshly isolated rat cardiac myocytes. Scatchard analysis of [3H]batrachotoxinin binding showed that Transcainide both reduced maximal binding and altered the KD for [3H]batrachotoxinin binding, indicating noncompetitive, allosteric inhibition. Inhibition by Transcainide of [3H]batrachotoxinin binding was reversible within 60 min. Transcainide had little effect on the k-1 of [3H]batrachotoxinin even at concentrations 1000-fold greater than its IC50, indicating a low affinity of Transcainide for activated channels. However, Transcainidee decreased the k + 1 of [3H]batrachotoxinin at a concentration very close to its IC50 concentration for inhibiting equilibrium [3H] batrachotoxin binding. The results are discussed in terms of a model in which Transcainide inhibits [3H] batrachotoxin binding by binding specifically to and stabilizing a nonactivated state of the cardiac sodium channel.[1]
Reduction of sodium current by Transcainide was concentration-dependent, with an ED50 of approximately 0.5 μM (n = 9).[2]