Describe the pharmacology of lignocaine.
Comprehensive answers included uses (including antiarrhythmic action and a role in analgesia), physical properties and preparations, pharmacodynamics and pharmacokinetics. Its mode of action should also have been described. Many candidates focussed on toxicity and its management but provided little information on pharmacodynamics and pharmacokinetics, commonly omitting factors which affect its systemic absorption. Other common omissions were the dose required for its local anaesthetic effect and for its antiarrhythmic effect.
| Class | Class Ib antiarrhythmic |
| Chemistry | Aminoamide |
| Routes of administration | IV, inhaled, subcutaneous |
| Dose |
Anaesthetic (regional infiltration) maximum dose 4mg/kg, with adrenaline 8mg/kg Infused dose for antiarrhythmic effect = 1-2mg/kg loading dose, |
| Absorption | Oral bioavailability = 35% |
| Solubility | pKa = 7.9; about 25% is not ionised at pH 7.4 |
| Distribution | VOD= 0.9L/kg; 70% protein-bound |
| Target receptor | Nav1.5 subunit of the fast voltage-gated sodium channels |
| Metabolism | Hepatic metabolism (90-95%) |
| Elimination | Minimally renally excreted; half-life 10-20 minutes following IV bolus, closer to 45-90 minutes with subcutaneous infiltration |
| Time course of action | Duration of action is similar to half-life |
| Mechanism of action | Regional anaesthesia, by differential block (pain and temperature finres are blocked earlist). With higher doses, also motor block. In toxicity, CNS effects (visual disturbances, perioral mumbness, delirium,seizures, coma) and cardiovascular side effects (initially tachycardia and hypertension followed by bradycardia, negative inotropy, vasodilation and arrhythmias) Does not prolong the QRS, and actually shortens the QT. |
| Clinical effects | Antiarrhythmic effect, analgesic and local anaesthetic effects. Lowers seizure threshold, causes CNS excitation. Does not prolong the QRS, and actually shortens the QT. |
| Single best reference for further information | Weinberg et al (2015) |
HOLMDAHL, M. H: SON. "Xylocain (lidocaine, lignocaine), its discovery and Gordh's contribution to its clinical use." Acta Anaesthesiologica Scandinavica 42 (1998): 8-12.
Eipe, N., S. Gupta, and J. J. B. E. Penning. "Intravenous lidocaine for acute pain: an evidence-based clinical update." Bja Education 16.9 (2016): 292-298.
Weinberg, Laurence, et al. "Pharmacokinetics and pharmacodynamics of lignocaine: A review." World Journal of Anesthesiology 4.2 (2015): 17-29.