Class: Local anaesthetic and class 1b antiarrhythmic
Pharmacuetics: colorless liquid, stored in acidic pH to remain soluble. 1% and 2% formulations common.
Dose: max subcut dose 3mg/kg; with adrenaline 7mg/kg. 1mg/kg IV dose for antiarrhythmic effect -> 1mg/kg/hr infusion. CC/CNS ratio 7:1 (plasma level for CNS toxicity << that for CVS toxicity).
A: 35% OBA
D: 0.9L/kg, 70% protein bound
M: Completely hepatically metabolised \(\to\) inactive metabolites
E: No renal elimination. T1/2=15 minutes IV, 1 hour subcut, duration of action \(\approx\) 1 half life
Mechanism:
- Unionized form diffuses across excitable cell membrane \(\to\) becomes ionized in more acidic ICF
- Binds to open state of fast sodium channel \(\to\) stabilize in inactive state
- Use-dependance = more frequent firing \(\to\) more efficacious block
Effects:
- Preferentially affect pain and temperature sensory fibers because C-fibers are unmyelinated
- Regional anaesthsia
- Motor block with higher exposure
- CNS effects - visual disturbamces, perioral numbness, progressing to seizure, coma.
- CVS effects - tachycardia and hypertension \(to\) bradycardia, negative inotropy, vasodilation, arrhythmia. QRS prolongation.