Contraindicated Drugs

All class Ia, 1c and class III antiarrhythmic drugs are contraindicated in overdose with most proarrhythmic drugs.

Phenytoin is contraindicated in theophylline poisoning and is ineffective in TCA poisoning.

Drugs that cause bradycardia (beta-blockers, magnesium and calcium channel blockers) should be used very cautiously as most toxins that cause tachyarrhythmias also may cause bradyarrhythmias that have a far worse prognosis.