Local Anesthetic Systemic Toxicity

Topic: Local Anesthetic Systemic Toxicity

Common abbreviation: LAST

Category: Dental anesthesia emergency; local anesthetic overdose or systemic toxicity

Relevant drugs: Lidocaine, articaine, mepivacaine, prilocaine, bupivacaine, topical anesthetics, and any combination of local anesthetics used in the same appointment.

This article is for dental education only. LAST is a rare but potentially life-threatening emergency. Every dental clinic using injectable or high-dose topical local anesthetics should have a written emergency plan, oxygen, monitoring strategy, trained staff, emergency contact pathway, and clear protocol for local anesthetic toxicity. Emergency treatment must follow local regulations, training level, and institutional guidance.

Local Anesthetic Systemic Toxicity occurs when a local anesthetic reaches toxic blood levels and affects the central nervous system and/or the cardiovascular system.

In dentistry, it may happen after accidental intravascular injection, excessive total dose, repeated cartridges without calculation, rapid injection, high-dose topical anesthetic exposure, or additive dosing from more than one local anesthetic.

The key safety principle is prevention: calculate the dose, aspirate, inject slowly, use the lowest effective amount, monitor the patient, and recognize early warning signs before severe toxicity develops.

• Best prevention: weight-based dose calculation, aspiration, slow injection, incremental dosing, and careful patient selection
• Common dental trigger: intravascular injection or repeated cartridges without total milligram calculation
• Early warning signs: metallic taste, tinnitus, circumoral numbness, dizziness, agitation, confusion, tremor
• Severe signs: seizure, respiratory depression, arrhythmia, hypotension, cardiovascular collapse, cardiac arrest
• Clinical priority: stop injecting immediately, call for help, support airway and breathing, treat seizures, and activate emergency protocol

• Dental anesthesia is common, so even rare complications must be planned for.
• Multiple cartridges may be used during difficult anesthesia, endodontics, surgery, or implant procedures.
• Different local anesthetics may be combined in one appointment, making total-dose calculation more complex.
• Children, low body weight adults, older adults, pregnant patients, and medically compromised patients may reach toxic levels with fewer cartridges.
• Highly vascular injection sites and accidental intravascular injection can increase systemic exposure rapidly.
• Symptoms may be confused with anxiety, vasovagal syncope, panic, epinephrine reaction, or hypoglycemia.
• Severe LAST can progress quickly and requires immediate emergency response.

• Accidental intravascular injection: especially when aspiration is not performed or injection is rapid.
• Overdose: too many cartridges for the patient’s body weight or medical status.
• Additive dosing: using more than one local anesthetic without calculating the total exposure.
• Repeated injections: common during difficult mandibular anesthesia or long surgical appointments.
• High-dose topical anesthetics: especially benzocaine or lidocaine sprays/gels used excessively or on mucosa.
• Reduced metabolism: liver disease, severe systemic illness, extreme age, or pregnancy-related pharmacologic changes.
• High-risk anesthetic selection: bupivacaine toxicity is especially concerning because of cardiotoxicity.

• Children and low body weight adults
• Older adults or frail patients
• Pregnant patients
• Patients with significant liver disease
• Patients with serious cardiac disease, conduction disorders, arrhythmia, or heart failure
• Patients with renal impairment or severe systemic illness
• Patients receiving multiple local anesthetics in the same appointment
• Patients undergoing long procedures requiring repeated injections
• Patients with a history of seizure disorder or neurologic vulnerability
• Patients with anxiety, because early symptoms may be misinterpreted or missed

Early LAST symptoms often involve the central nervous system. A patient may report or show:

• Metallic taste
• Numbness around the mouth or tongue numbness beyond the expected injection area
• Tinnitus or hearing changes
• Dizziness, lightheadedness, or visual disturbance
• Agitation, anxiety-like behavior, restlessness, or confusion
• Slurred speech
• Tremor, muscle twitching, or shaking
• Nausea or unusual feeling shortly after injection
• Sudden change in behavior after local anesthetic administration

• Generalized seizure
• Loss of consciousness or reduced responsiveness
• Respiratory depression or apnea
• Severe hypotension or cardiovascular collapse
• Bradycardia, tachycardia, ventricular arrhythmia, or conduction disturbance
• Chest pain or signs of myocardial ischemia
• Cardiac arrest
• Persistent neurologic symptoms after injection
• Symptoms that appear after a delay, especially after large total doses or topical anesthetic exposure

Do not wait for all classic symptoms. LAST may present with central nervous system signs, cardiovascular signs, or both. A sudden neurologic or cardiovascular change after local anesthetic injection should be treated as LAST until proven otherwise.

• Take a focused medical history before anesthesia.
• Record body weight when dose may be close to the limit, especially in children and small adults.
• Calculate the maximum dose in milligrams before repeated injections.
• Know the milligrams per cartridge for each anesthetic concentration.
• Count all local anesthetics used in the appointment as additive exposure.
• Aspirate before injection and re-aspirate if the needle position changes.
• Inject slowly and incrementally rather than rapidly.
• Use the lowest effective dose for the planned procedure.
• Prefer safer alternatives or dose reduction in medically compromised patients.
• Monitor the patient verbally and visually during and after injection.

• 2% lidocaine: 20 mg/mL → about 36 mg in a 1.8 mL cartridge
• 4% articaine: 40 mg/mL → about 72 mg in a 1.8 mL cartridge
• 3% mepivacaine: 30 mg/mL → about 54 mg in a 1.8 mL cartridge
• 4% prilocaine: 40 mg/mL → about 72 mg in a 1.8 mL cartridge
• 0.5% bupivacaine: 5 mg/mL → about 9 mg in a 1.8 mL cartridge

This box is for rapid study memory only. Final dose limits must follow the exact product label, patient weight, medical status, and local clinical guidance.

1. Stop injecting immediately.
2. Call for help and activate the clinic emergency plan.
3. Position the patient safely and remove instruments from the mouth.
4. Assess responsiveness, airway, breathing, circulation, and vital signs.
5. Give high-flow oxygen and support ventilation if needed.
6. Call emergency medical services early if symptoms are significant, progressive, or uncertain.
7. Protect the patient from injury during seizure activity.
8. Treat seizures according to local emergency protocol; benzodiazepines are generally preferred when available and within the clinician’s scope.
9. Prepare for basic life support and CPR if cardiovascular collapse occurs.
10. Use 20% lipid emulsion only according to training, availability, and local protocol; continue care until emergency help arrives.

LAST resuscitation is not exactly the same as routine cardiac arrest management. Specialist guidelines emphasize early lipid emulsion consideration, seizure control, airway and oxygenation, and caution with certain cardiovascular drugs. Dental teams should keep an updated LAST checklist accessible wherever local anesthesia is used.

20% lipid emulsion is an important treatment used in severe LAST, especially when seizures, arrhythmias, hypotension, or cardiovascular instability occur.

Commonly referenced ASRA-style dosing for patients under 70 kg: bolus about 1.5 mL/kg over 2–3 minutes, then infusion about 0.25 mL/kg/min. If instability persists, repeat bolus and increase infusion according to protocol.

Commonly referenced ASRA-style dosing for patients over 70 kg: bolus about 100 mL over 2–3 minutes, then infuse about 250 mL over 15–20 minutes, with escalation if unstable according to protocol.

This dosing section is for recognition and training context only. In real emergencies, use the clinic’s official LAST checklist, local emergency protocol, and trained medical support.

Several events can look similar during dental treatment. The safest approach is to treat serious symptoms immediately while considering the cause.

• Vasovagal syncope: pallor, sweating, nausea, slow pulse, fainting; often triggered by fear or pain.
• Epinephrine reaction: sudden palpitations, tremor, anxiety-like feeling, tachycardia; often short-lived.
• Panic attack: hyperventilation, fear, tingling, chest tightness, but usually no toxic neurologic progression.
• Hypoglycemia: sweating, tremor, confusion, hunger, weakness, possible loss of consciousness.
• Allergy/anaphylaxis: urticaria, swelling, wheezing, hypotension, airway symptoms.
• Methemoglobinemia: cyanosis, shortness of breath, low oxygen saturation not improving as expected with oxygen, especially after prilocaine or benzocaine.
• LAST: neurologic warning signs, seizure, arrhythmia, hypotension, or collapse after local anesthetic exposure.

The best LAST treatment is prevention. Before adding another cartridge, pause and ask: How many milligrams have I already given? What is the patient’s weight? Did I aspirate? Is this still local anesthetic failure, or do I need to change technique, wait longer, or treat the source differently?

• Seizure or repeated muscle twitching after injection
• Confusion, agitation, slurred speech, or altered consciousness after local anesthesia
• Metallic taste, tinnitus, circumoral numbness, or visual disturbance after injection
• Severe dizziness, collapse, fainting with prolonged recovery, or unresponsiveness
• Chest pain, arrhythmia, severe palpitations, hypotension, or cardiovascular instability
• Slow breathing, apnea, cyanosis, or need for assisted ventilation
• Symptoms after high total dose, intravascular injection suspicion, or use of multiple anesthetics
• Any suspected LAST, even if symptoms are incomplete or atypical

• Lidocaine + Epinephrine
• Articaine + Epinephrine
• Mepivacaine
• Prilocaine
• Bupivacaine + Epinephrine
• Epinephrine / Adrenaline
• Felypressin / Octapressin
• Topical benzocaine and methemoglobinemia
• 20% lipid emulsion therapy
• Dental emergency preparedness

Local Anesthetic Systemic Toxicity is a rare but serious dental anesthesia emergency caused by toxic systemic exposure to local anesthetics. It may result from intravascular injection, excessive dose, additive dosing, rapid injection, high-dose topical use, or reduced patient tolerance. Early symptoms include metallic taste, tinnitus, circumoral numbness, dizziness, agitation, confusion, tremor, and slurred speech. Severe toxicity may progress to seizures, respiratory depression, arrhythmia, cardiovascular collapse, or cardiac arrest. Prevention depends on dose calculation, aspiration, slow incremental injection, patient-specific risk assessment, and immediate recognition. If LAST is suspected, stop injecting, call for help, support airway and breathing, treat seizures, prepare for resuscitation, and follow a LAST protocol including 20% lipid emulsion when indicated and available.