Lignocaine
Chemical
Prototype amide LA
Use
1.Reversible neuronal blockade
2.Class Ib anti-arrythmic
3.Analgesic infusion
Presentation
IV: Clear colourless soln
1-2%
+/- Adr
Also available as a spray, viscous & topical cream
Dose
1mg/kg
Epidural = 300-500mcg
Anti-arrythmic = Loading 1mg/kg IV over 2mins, then 1-4mg/min to achieve plasma levels 1-5mcg/ml
Toxic Dose
3mg/kg
7mg/kg with Adrenaline
Onset
Rapid. Often used w Adr to prolong conduction blockade and decrease systemic absorption
Route
Onset
Duration
Plain
+Adr
Topical
5min
15-30min
Infiltration
2min
75min
400min
Major N block
15-45min
60min
120min
Epidural / Caudal
15min
60min
100min
Duration
15-60mins
MoA
Unionised diffuses across neuronal cell memb
Becomes ionized within cell
Binds and OPENS Na+ ch → blocks them
↓depol of membrane → cardiac myocyte, motor & sensory n fibre Aps blocked
Cardiac myocyte: Ph 0 reduced & AP duration increases
PM cell: Ph 5 prolonged →↓automaticity
PK
A
25% UNionised at pH 7.4
Depends on site
IC > epidural > SC
Adr ↓plasma peak 30%
OBA 25% – high 1st pass
D
70% PPB a1 glycoprotein (duration)
Vd 1.5L/kg
Lipid solubility high (potency) → crosses BBB
M
N-dealkylation & hydrolysis liver. Active metabolibtes MEGX & GX can accumulate and cause neurotoxicity
Lower seizure threshold
Lignocaine is a high extraction drug (clearance depends on HBF)
Clearance 10ml/kg/min
E
Urine excretion metabolites
10% unchanged
t1/2b 96 mins (but↑ x5 in patients w hepatic dysfn)
PD
CNS
Reversible neuronal blockade
Analgesia w IV injection
CVS
↓Ph 4 rate depol
↓automaticity
RESP
bronchodilation
AE
MetHb
Narrow therapeutic window
<5mcg/ml
>5mcg/ml → CNS → confusion, agitation, paraesthesia
>20mcg/ml → H → AV block, unresponsive, hypotension, cardiac arrest