Class 1 Anti-Arrhythmics
Membrane Stabilising Drugs
Examples
- Class 1A - Disopyramide
- Class 1B - Lidocaine, Mexiletine
- Class 1C - Flecainide
Indications
Class 1A: atrial fibrillation, flutter; supraventricular & ventricular tachyarrhythmias
Class 1B: Ventricular tachyarrhythmias
Class 1C: Life-threatening supraventricular tachyarrhythmias and verntricular tachyarrhythmias
Contraindications
Contraindications
- Heart failure
- Heart block
- Ischaemic heart disease (flecainide)
Caution
- Pregnancy
- Prostatic enlargement
- Glaucoma
- Hepatic impairment
- Renal impairment
Mechanism
Class 1 anti-arrhythmics inhibit sodium channels, their different properties are due to different speeds of binding. Class 1A drugs act to prolong the cardiac action potential. 1B drugs shorten the action potential. 1C drugs do not change the action potential.
Administration
Oral or Intravenous administration depending on the circumstance
Adverse Reactions
- Class 1 drugs are arrhythmogenic and may prolong the QT interval
- Anticholinergic effects
- Seizures (Class 1C)
Interactions
Some class 1 drugs are metabolised by the cytochrome P450 system, making them susceptible to drug-drug interactions. Avoid concomitant use with other drugs that may prolong the QT interval (e.g. amiodarone, anti-histamines).
Avoid with other drugs which have a negatively inotropic effect.
Arrhythmias are more common in patients with hypokalaemia, making the use of these drugs potentially problematic alongside diuretics, etc which lower potassium.
Other drugs with anti-cholinergic side effects may exacerbate those of Class 1 drugs.
Education
Certain tachyarrhythmias can be precipitated by patient activities (e.g. drinking coffee). In these cases, patients should be warned to avoid triggers where possible. Non-pharmacological methods can be used to terminate some types of SVT and patients can be taught these.
Pharmacokinetics
Disopyramide is 75% renally excreted and dose should be halved in renal impairment. Half-life can be prolonged in hepatic impairment and dose may need reduction.
