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Increased incidence of side effects after encainide: a newly developed antiarrhythmic drug
Insights
Encainide, a new antiarrhythmic drug, caused significant side effects in patients with ventricular ectopies, leading to study termination. Its efficacy was insufficient to overcome adverse events, making it unsuitable as a first-choice treatment.
Area of Science:
- Cardiology
- Clinical Pharmacology
Background:
- Ventricular ectopies are a common cardiac arrhythmia.
- Class I antiarrhythmic agents are used to treat arrhythmias.
- Encainide is a novel Class I antiarrhythmic agent.
Purpose of the Study:
- To compare the efficacy and safety of encainide with mexiletine in patients with chronic complex ventricular ectopies.
- To evaluate the antiarrhythmic effect of encainide at increasing dosages.
- To assess the incidence of side effects associated with encainide treatment.
Main Methods:
- A clinical trial involving nine patients with documented ventricular ectopies.
- 24-h Holter monitoring and treadmill exercise testing were used for efficacy assessment.
- Dosage escalation of encainide from 25 to 75 mg three times daily.
- Clinical follow-up to monitor for adverse events.
Main Results:
- A high incidence of minor side effects (headache, dizziness, blurred vision, tremor, nausea) was observed.
- Adverse effects emerged before satisfactory suppression of ectopic activity.
- Dosage increment of encainide was prohibited due to side effects.
- Encainide did not achieve satisfactory suppression of ventricular ectopies in this patient group.
Conclusions:
- Encainide is associated with a high rate of side effects that limit its therapeutic utility.
- The observed adverse effects of encainide emerged before achieving adequate antiarrhythmic control.
- Encainide is not recommended as a first-choice antiarrhythmic drug for routine clinical use in patients with ventricular ectopies.
Abstract:
In a clinical trial the efficacy of encainide, a newly developed class I antiarrhythmic agent, was compared with the well-known mexiletine. Nine patients with different underlying cardiac disease and chronic complex ventricular ectopies (documented by 24-h Holter monitoring, confirmed during the initial placebo period) entered the study. The dosage of encainide was increased from 25 to 75 mg three times daily and the antiarrhythmic effect monitored by repeated 24-h Holter registration and in some patients by treadmill exercise testing. During the clinical followup we noted a high incidence of so-called "minor side effects" (headache, dizziness, blurred vision, tremor, and nausea), which caused us to terminate the study. In all instances adverse effects emerged before ectopic activity was suppressed satisfactorily prohibiting further increment of dosage. These results indicate that encainide cannot be regarded as an antiarrhythmic drug of first choice in routine clinical application.