Class 1 Anti-Arrhythmics Flashcards
Examples: Class 1A
- Quinidine
- Disopyramide
Example: Class 1B
- Lidocaine
Example: Class 1C
- Flecainide
Indications of class 1’s?
- Tachyarrhythmias
What are the contraindications of class 1A’s?
- Heart failure
- Heart block
- Ischaemic heart disease (flecainide)
Cautions for use of class 1’s?
- Pregnancy
- Prostatic enlargement
- Glaucoma
- Hepatic impairment
- Renal impairment
How do class 1’s work?
- Inhibit sodium channels
How do A, B and C differ if they act on the same channels?
- They have different speeds of binding
What effect do 1A’s (quinidine and disopyramide) have?
- Prolong cardiac action potential
What effect do 1B’s (lidocaine) have?
- Shorten cardiac action potential
What effect do 1C’s (flecainide) have?
- Do not affect action potential
How are class 1’s administered?
- Oral or IV depending on circumstance
What adverse reactions are there for class 1 anti arrhythmics?
- Arrhythmogenic and may prolong QT interval
- Anticholinergic effects
- Seizures (flecainide)
How are some class 1’s metabolised?
- Through the cytochrome P450 system so very susceptible to drug interactions
What drugs should you avoid copharmacy with?
- Drugs that may prolong QT interval (e.g. amiodarone, antihistamines)
- Drugs which have a negatively ionotropic effect
What other (metabolic) condition commonly goes along with arrhythmias?
Hypokalaemia
What complication does the hypokalaemia cause?
- Can’t use diuretics with anti-arrhythmics as they lower potassium further
What should patients be warned to avoid because of the tachyarrhythmic side effect?
- Avoid triggers that cause tachyarrhythmias such as drinking coffee
What should be done to doses of disopyramide in patients with renal failure?
- Dose should be halved as 75% of the drug excreted through renal
What can happen to the half life of some class 1 antiarrhythmics during hepatic impairment?
- Can be increased
