Unit Converter
Lidocaine
(Local Anesthetic & Antiarrhythmic – Therapeutic Drug Monitoring, Toxicity & Pharmacokinetics)
Synonyms
- Lidocaine
- Lignocaine
- Xylocaine
- Antiarrhythmic Class Ib agent
- Amide local anesthetic
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Molecular Weight
Lidocaine = 270.37 g/mol
Key Unit Conversions
1 mg/L = 3.70 µmol/L
1 mg/dL = 10 mg/L = 37.0 µmol/L
1 µg/mL = 1 mg/L
1 µmol/L = 0.27 mg/L
mg% = mg/dL
Description
Lidocaine is an amide-type local anesthetic and Class Ib antiarrhythmic.
It works by:
- Blocking voltage-gated sodium channels
- Reducing neuronal excitability
- Suppressing ventricular arrhythmias
Used for:
- Local and regional anesthesia
- Treatment of ventricular arrhythmias (post-MI, cardiac arrest)
- IV infusion in ICU settings
- Topical and infiltration anesthesia
- Neuropathic pain (selected cases)
Therapeutic drug monitoring (TDM) is essential during IV infusion due to narrow therapeutic range and risk of CNS/cardiac toxicity.
Physiological & Pharmacological Effects
1. Local Anesthesia
- Prevents nerve impulse conduction
- Rapid onset, moderate duration
2. Antiarrhythmic Action
- Decreases automaticity
- Shortens action potential duration
- Effective for ischemic ventricular myocardium
- First-line in certain ventricular tachyarrhythmias
3. CNS Effects
Dose-dependent:
- Lightheadedness → Tremors → Seizures → Coma
4. Cardiovascular Effects
- Hypotension
- Bradyarrhythmias
- Reduced myocardial contractility at high doses
Clinical Significance
1. Therapeutic Monitoring
Used particularly when lidocaine is given IV for:
- Ventricular arrhythmias
- Digitalis toxicity arrhythmias
- Post-resuscitation management
TDM ensures:
- Effective antiarrhythmic level
- Avoidance of toxicity
- Adjustments based on liver function & drug interactions
Therapeutic & Toxic Ranges
(Mayo + ARUP + AACT toxicology data)
Therapeutic Range
- 1.5 – 5.0 µg/mL
( = 1.5 – 5 mg/L, ≈ 5.6 – 18.5 µmol/L)
Toxic Concentration
- > 6 µg/mL → Early toxicity
- > 8 µg/mL → Significant CNS symptoms
- > 10 µg/mL → Severe neurotoxicity & cardiac toxicity
- > 15 µg/mL → Life-threatening
Critical Signs of Toxicity
- Circumoral numbness
- Tinnitus
- Visual disturbances
- Tremors
- Seizures
- Hypotension
- Ventricular arrhythmias
- Cardiac arrest
Pharmacokinetics
- Absorption: rapid via IV, variable via topical
- Distribution: high protein binding (~70% to α-1-acid glycoprotein)
- Metabolism: liver (CYP1A2, CYP3A4)
- Half-life: 90–120 minutes (prolonged in liver disease, CHF)
- Excretion: renally as metabolites
High-risk groups for toxicity:
- Liver disease
- Heart failure
- Elderly
- Renal impairment
- Drug interactions (beta blockers, CYP inhibitors)
Reference Intervals
Because lidocaine is not endogenous, reference = therapeutic ranges.
- Normal (not treated): undetectable
- Therapeutic (antiarrhythmic): 1.5–5.0 µg/mL
- Toxic: >6 µg/mL
Diagnostic Uses
1. Therapeutic Drug Monitoring
During IV infusion in:
- ICU
- Post-MI VT/VF
- Arrhythmia management
2. Suspected Drug Toxicity
Measure levels if:
- Neurological symptoms
- Cardiovascular instability
- Overdose (rare)
3. Evaluate Drug Interactions
CYP3A4 or CYP1A2 inhibitors raise lidocaine levels.
4. Post-Mortem Toxicology
Lidocaine commonly used in resuscitation; levels help in interpretation.
Analytical Notes
- Serum or plasma (EDTA) acceptable
- Avoid hemolysis
- Assayed by immunoassay or LC-MS/MS
- Consider timing relative to infusion (steady state ~12 hours)
- Protein binding changes alter total vs free levels
Clinical Pearls
- CNS symptoms precede cardiovascular collapse in toxicity.
- Hypoxia, acidosis & hypercapnia greatly enhance lidocaine toxicity.
- Elderly and liver-diseased patients require lower doses.
- Lidocaine is more effective in ischemic ventricular tissue than healthy tissue.
- Epinephrine-containing local anesthetic mixtures delay systemic absorption.
Interesting Fact
Lidocaine was discovered in 1943 and was the first synthetic amide anesthetic, revolutionizing both anesthesia and cardiac arrhythmia management.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Therapeutic Drug Monitoring
- AACT / EAPCCT Toxicology Guidelines
- Mayo Clinic Laboratories - Lidocaine Level
- ARUP Consult - Cardiac Drug Monitoring
- Goodman & Gilman’s Pharmacological Basis of Therapeutics
- NIH / MedlinePlus - Lidocaine