Systemic toxicity
Systemic toxicity can follow inadvertent intravascular injection of local anaesthetic, excessive dose administration, impaired drug clearance or, rarely, rapid systemic absorption.
Adverse systemic effects are usually seen in a continuum as plasma concentration increases, so use the lowest effective dose and do not exceed the maximum recommended dose (see Doses of local anaesthetics in dentistry).
The clinical presentation of systemic toxicity is variable and can include neurological, psychiatric, cardiovascular and respiratory effects, allergic reactions and, rarely, methaemoglobinaemia1. Minor central nervous system (CNS) effects (eg restlessness, anxiety, tinnitus, dizziness, blurred vision, tremors, CNS depression, drowsiness) are early indicators of systemic toxicity. However, cardiovascular effects may occur before CNS effects if a longer-acting local anaesthetic is used (particularly bupivacaine). Serious systemic effects include seizures and cardiovascular toxicity.
Allergic reactions may be caused by the local anaesthetic or another component in the solution.
Methaemoglobinaemia is mainly associated with prilocaine (particularly at doses over 600 mg) and benzocaine, but is occasionally reported with lidocaine, articaine and tetracaine. Slate-grey skin discolouration and cyanosis are the most distinct features. Methaemoglobinaemia can be life threatening and requires emergency referral to hospital (for first-aid management in dental practice, see here; for the medical management of methaemoglobinaemia, see Methaemoglobinaemia).
If signs of systemic toxicity occur (or are suspected), stop administration of the local anaesthetic and provide appropriate management (in dental practice, see here for first-aid management of medical emergencies). For the medical management of local anaesthetic poisoning, see Local anaesthetic poisoning.