Enkaid (Encainide Hydrochloride) - Drug Interactions, Contraindications, Overdosage

DRUG INTERACTIONS

Drug Interactions

In prospective studies single and multiple doses of ENKAID have had no significant effect on serum digoxin levels. Likewise, combined digoxin/ENKAID therapy has been administered without adverse effects.

Experience has indicated no obvious problems with the combined use of ENKAID and other antiarrhythmic agents, diuretics, beta blockers or calcium channel blockers. However, because of possible additive pharmacologic effects, caution is indicated when ENKAID is used with another antiarrhythmic agent or any other drug that affects cardiac conduction.

Cimetidine (300 mg q.i.d.) increases plasma concentrations of encainide and its active metabolites. Although no clinically significant consequences have been reported, caution should be utilized when the two drugs are administered simultaneously. ENKAID dosage should be reduced if cimetidine is to be given to a patient taking ENKAID.

In vitro binding studies with several drugs that may be administered concomitantly have not revealed any significant alteration in the protein binding of encainide, ODE, or MODE; nor did high concentrations of encainide and its metabolites alter the binding of the other medications including such highly protein bound drugs as warfarin.

OVERDOSAGE

Intentional or accidental overdosages with ENKAID have resulted in death.

Signs, Symptoms, and Laboratory Findings Associated with an Overdosage of the Drug

Overdosage with ENKAID may produce excessive widening of the QRS complex and QT interval and AV dissociation. Hypotension, bradycardia and finally asystole may develop. A variety of conduction disturbances may be observed. Convulsions have occurred in one case of intentional overdosage.

Oral LD₅₀ of the Drug in Animals

The acute, oral LD₅₀ values for encainide are estimated to be 80 mg/kg in the mouse and 59 mg/kg in the rat.

Recommended General Treatment Procedures

In the event of overdosage with ENKAID, patients should be hospitalized and provided with cardiac monitoring and advanced life support systems. No specific antidote for ENKAID has been identified; however, one report has suggested hypertonic sodium bicarbonate may be useful in managing the cardiac toxicity associated with an ENKAID overdosage. Acute overdosages should be treated by gastric lavage followed by activated charcoal. Treatment of overdosage should be supportive.

CONTRAINDICATIONS

ENKAID is contraindicated in patients with preexisting second- or third-degree AV block, or with right bundle branch block when associated with a left hemiblock (bifascicular block), unless a pacemaker is present to sustain the cardiac rhythm should complete heart block occur. ENKAID is also contraindicated in the presence of cardiogenic shock or known hypersensitivity to the drug.