Local anesthetic systemic toxicity


  • Acronym: LAST
  • Life-threatening adverse reaction to local anesthetic toxicity.
  • Incidence = ~0.2% of nerve blocks
  • Generally occurs within minutes of injection


  • Injection of local anesthetic into systemic circulation
    • Most common source of toxicity[2]
    • Intravascular injection can cause toxicity below the maximum recommended dose[3]
  • Exceeding the maximum dose of local anesthetic (see table below)
  • Absorption of anesthetic into systemic circulation by injection into extremely vascular area.

Maximum Doses of Anesthetic Agents

Agent Without Epinephrine With Epinephrine Duration Notes
Lidocaine 5 mg/kg (max 300mg) 7 mg/kg (max 500mg) 30-90 min
  • 1% soln contains 10 mg/ml
  • 2% soln contains 20 mg/ml
Mepivicaine 7 mg/kg 8 mg/kg
Bupivicaine 2.5 mg/kg (max 175mg) 3 mg/kg (max 225mg) 6-8 hr
  • 0.5% soln contains 5 mg/ml
  • May cause cardiac arrest if injected intravascularly
  • Do not buffer with bicarbonate
Ropivacaine 3 mg/kg
Prilocaine 6 mg/kg
Tetracaine 1 mg/kg 1.5 mg/kg 3hrs (10hrs with epi)
Procaine 7 mg/kg 10 mg/kg 30min (90min with epi)

Diphenhydramine as Local Anesthetic

  • Injectable 1% diphenhydramine (10 mg/mL) can be used as a local anesthestic alternative to ester/amide anesthetics[4]
    • Sodium channel blocker mechanism
    • 1-2 mL of 1% diphenhydramine at a time, to not exceed excessive sedation dose
    • Typical vial is 50 mg/mL, so to make 10 mg/mL:
      • 10 mL NS removed from 50 mL vial
      • Add 10 mL of 50 mg/mL diphenhydramine to 40 mL of NS
      • Sedation is dose related and is similar to what would be expected for IM doses
      • Relative contraindications are the same for IM diphenhydramine administration

Clinical Features

Clinical course tends to be a dose-dependant progression from CNS symptoms to CVS symptoms and death[5]

Differential Diagnosis

  • Anaphylaxis
  • Anxiety
  • Methemoglobinemia - local anesthestics oxidize Fe2+ to Fe3+ in Hb

Sodium Channel Blockade Toxidrome


  • Clinical diagnosis


  • Directed by clinical picture
  • Blood levels of anesthetic are available, but not clinically useful.



  • Admit

See Also

External Links


  1. 1.0 1.1 Fencl JL. Local anesthetic systemic toxicity: perioperative implications. AORN J. 2015 Jun;101(6):697-700.
  2. Sztajnkrycer MD. Local Anesthetics. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank's Toxicologic Emergencies, 11e. McGraw-Hill; Accessed November 29, 2020. https://accessemergencymedicine.mhmedical.com/content.aspx?bookid=2569&sectionid=210274249
  3. Scott DB. "Maximum recommended doses" of local anaesthetic drugs. Br J Anaesth. 1989 Oct;63(4):373-4. doi: 10.1093/bja/63.4.373. PMID: 2818914.
  4. Pavlidakey PG et al. Diphenhydramine as an Alternative Local Anesthetic Agent. J Clin Aesthet Dermatol. 2009 Oct; 2(10): 37–40.
  5. Kamel I, Trehan G, Barnette R. Intralipid Therapy for Inadvertent Peripheral Nervous System Blockade Resulting from Local Anesthetic Overdose. Case Reports in Anesthesiology. 2015;2015:486543. doi:10.1155/2015/486543.
  6. GlobalRPH. Management of Local Anesthetic Emergencies. http://www.globalrph.com/local-anesthetics.htm
  7. 7.0 7.1 Dillane D, Finucane BT. Local anesthetic systemic toxicity. Can J Anaesth. 2010 Apr;57(4):368-80.
  8. per ASRA (Am Soc of Regional Anesthesia)