Toxic dose

Parenteral toxic doses for local anaesthetic drugs are not well defined, and depend on the drug used and whether a coformulation with adrenaline (epinephrine) has been given¹. The maximum recommended regional doses for local anaesthetics can be used as a guide (see Maximum recommended regional dose for local anaesthetics); however, local anaesthetic toxicity can occur at or below the maximal recommended regional dose if the drug is inadvertently administered into the intravascular, intrathecal or intraspinal spaces.

Table 1. Maximum recommended regional dose for local anaesthetics
[NB1]
Drug	Maximum dose if administered without adrenaline (epinephrine)	Maximum dose if administered with adrenaline (epinephrine)
lidocaine	3 mg/kg	7 mg/kg
bupivacaine	2 mg/kg	2 mg/kg
ropivacaine	3 mg/kg	3 mg/kg
prilocaine	6 mg/kg	not applicable
articaine	not applicable	7 mg/kg
mepivacaine	5 to 7 mg/kg	6.6 mg/kg
EMLA [NB2] topical cream or patch	complex; dose varies by thickness of cream, and area and duration of application	not applicable
Note: EMLA = eutectic mixture of local anaesthesia NB1: Toxicity of any local anaesthetic drug may occur at or below these doses if inadvertently administered to the intravascular, intrathecal or intraspinal spaces. NB2: EMLA contains lidocaine 2.5% and prilocaine 2.5%. One gram of EMLA cream contains 25 mg each of lidocaine and prilocaine, and is approximately the size of a small coin or the length of 3.5 cm.

Ingestion of more than 6 mg/kg of lidocaine is potentially toxic in a child. Benzocaine² toxicity is unlikely after ingestions of less than 20 mg/kg, although significant poisoning has been reported at lower doses in children younger than 6 months. Cinchocaine³ is particularly toxic and significant poisoning can occur following ingestions as low as 0.5 mg/kg.

Topical application of local anaesthetic creams and gels can cause methaemoglobinaemia if used in excess of the recommended doses.

¹ Adrenaline (epinephrine) is coformulated with some local anaesthetic drugs (eg bupivacaine, lidocaine) for parenteral use. Adrenaline’s vasoconstrictor effect slows systemic absorption of the local anaesthetic from the injection site. This prolongs the local anaesthetic effect and reduces the likelihood of systemic toxicity.Return

² Benzocaine is a topical local anaesthetic commonly used for oropharyngeal pain relief (eg for pharyngitis or mouth ulcers).Return

³ Cinchocaine is a topical local anaesthetic commonly used for anorectal pain relief (eg for haemorrhoids).Return