Phenytoin as an effective treatment for polymorphic ventricular tachycardia due to QT prolongation in a patient with multiple drug intolerances

Abstract

SUMMARYWe present a case of a 69-year-old woman presenting with polymorphic ventricular tachycardia caused by QT prolongation. Owing to known intolerances to a majority of antiarrhythmic medications, one remaining option was to initiate phenytoin. Phenytoin's narrow therapeutic window, multiple drug interactions and side effect profile make it an infrequently used antiarrhythmic. It is, however, a potent antiarrhythmic agent, which may be useful in treatment of ventricular tachycardia, especially in patients with multiple drug intolerances. BACKGROUND

Unusual Cause of Bidirectional Ventricular Rhythm

“…A range of 10% to 15% of patients with genetically defined LQTS may present with baseline normal QTc (10) . Phenytoin, a Class Ib antiarrhythmic agent, can reduce the duration of the action potential by inhibiting the slow sodium current and the inward calcium current in the plateau phase of action potential in Purkinje fibers (11) , and clinical reports of phenytoin effectiveness in torsades de pointes, even in refractory cases, has been published (12) . The unique response of arrhythmia to phenytoin may be a phenotypical expression of the complex electrophysiological milieu in the patient with myocardial disarray, fibrosis, and mutations in the TTN and KCNH2 genes.…”

Complexity of ranolazine and phenytoin use in an infant with long QT syndrome type 3

“…It has effects on Na + , Ca 2+ , and K + channels in cardiac myocytes and Purkinje fiber cell membranes. Inhibition of rapid inward Na + current shortens the action potential and reduction of voltage-dependent calcium current reduces the rate of depolarization in the plateau phase of the cardiac action potential and increases the refractory period, thus preventing EADs 8 . The phenytoin trough level was maintained at the high therapeutic range (15–20 mcg/mL).…”

“…Inhibition of rapid inward Na + current shortens the action potential and reduction of voltage-dependent calcium current reduces the rate of depolarization in the plateau phase of the cardiac action potential and increases the refractory period, thus preventing EADs. 8 The phenytoin trough level was maintained at the high therapeutic range (15–20 mcg/mL). The addition of phenytoin resulted in a marked decline in ranolazine levels, as phenytoin is a potent inducer of CYP3A.…”

Multiple Drug Intolerance Syndrome: An Underreported Distinct Clinical Entity

“…Yager et al used phenytoin as an alternative to antiarrhythmic drugs in patients with multiple drug intolerances for treating ventricular tachycardia [33].…”