Risk factors for toxicity

The toxicity of a local anaesthetic is influenced by:

• the specific local anaesthetic used (eg bupivacaine is more toxic than lidocaine)
• whether a coformulation with adrenaline has been used¹
• route of administration (eg intravenous injection is more likely to cause toxicity than other routes)
• method of administration (eg an intravenous bolus injection is likely to result in a higher peak concentration than an infusion)
• site of administration (eg systemic absorption through skin is slower than through mucous membranes)
• vascularity of surrounding tissues (vascularity enhances absorption)
• patient-specific factors (eg pre-existing cardiac disease may compound drug toxicity).

A local anaesthetic block can cause toxic effects in itself, separate from the toxicity of the drug (eg hypotension due to a spinal or epidural block).