What level of intravenous (IV) lidocaine causes toxicity?

From the Guidelines

Lidocaine toxicity typically occurs at serum concentrations above 5 micrograms per milliliter (mcg/mL), with serious toxicity more likely above 10 mcg/mL, corresponding to doses exceeding 4-5 mg/kg of body weight for IV administration, as suggested by 1.

Key Points to Consider

• Early signs of toxicity include perioral numbness, metallic taste, lightheadedness, tinnitus, and visual disturbances, which can progress to more severe symptoms such as confusion, slurred speech, muscle twitching, seizures, respiratory depression, cardiovascular depression, and potentially cardiac arrest.
• Factors that increase toxicity risk include liver disease, heart failure, shock, acidosis, and concurrent use of beta-blockers or cimetidine, as lidocaine is metabolized by the liver, making hepatic impairment a significant risk factor for toxicity.
• When administering IV lidocaine, it is crucial to give it slowly (50-100 mg over 2-5 minutes) with continuous cardiac monitoring and immediate access to resuscitation equipment, as recommended by 1.
• Treatment of toxicity includes stopping the infusion, supporting vital functions, and potentially administering lipid emulsion therapy for severe cases.

Administration Guidelines

• Administration should be based on lean body weight, with caution and reduced infusion rates in patients over 70 years of age, those with congestive heart failure, cardiogenic shock, hepatic dysfunction, severe renal dysfunction, or preexisting neurologic dysfunction, as outlined in 1.
• Measurement of serum levels is recommended with prolonged or high infusion rates or changes in neurologic condition.

Monitoring and Support

• Continuous cardiac monitoring is essential during IV lidocaine administration, and immediate access to resuscitation equipment is critical in case of toxicity.
• Patients should be closely monitored for early signs of toxicity and managed promptly to prevent progression to more severe symptoms.

From the FDA Drug Label

Objective adverse manifestations become increasingly apparent with increasing venous plasma levels above 6. 0 mcg free base per mL. In the rhesus monkey arterial blood levels of 18–21 mcg/mL have been shown to be threshold for convulsive activity. The level of IV lidocaine that causes toxicity is above 6.0 mcg free base per mL, with convulsive activity threshold at 18-21 mcg/mL 2.

• Key points:
  • Venous plasma levels above 6.0 mcg free base per mL may cause adverse manifestations
  • Arterial blood levels of 18-21 mcg/mL may cause convulsive activity
  • These values are based on studies in rhesus monkeys and may not directly translate to humans.

From the Research

Lidocaine Toxicity

• Lidocaine is a commonly used anesthetic that can cause systemic effects involving the cardiovascular and neurologic systems, especially at high doses or with intravenous administration 3, 4.
• The level of IV lidocaine that causes toxicity is not strictly defined, as toxicity can occur despite therapeutic dosages and low serum concentrations 3.
• Symptoms of systemic lidocaine toxicity include perioral numbness, seizure-like activity, confusion, altered mental status, and cardiac arrhythmias 3, 4, 5.
• Intravenous lipid emulsion (ILE) has been shown to be effective in treating lidocaine toxicity, and its use should be considered in cases of suspected toxicity 3, 6, 5.

Risk Factors for Toxicity

• High doses or intravenous administration of lidocaine increase the risk of systemic toxicity 3, 4.
• Patients with pre-existing medical conditions or those taking other medications may be at higher risk of lidocaine toxicity 4.
• A low threshold of suspicion for local anesthetic systemic toxicity is necessary when patients present with neurologic or cardiovascular symptoms following exposure to lidocaine 3.

Treatment of Toxicity

• Prompt recognition and treatment of lidocaine toxicity are crucial to prevent serious complications and improve outcomes 4, 6, 5.
• Discontinuation of lidocaine and administration of ILE are key components of treatment 3, 4, 6, 5.
• Benzodiazepines may also be used to manage seizure-like activity and other neurologic manifestations of toxicity 4.