What is the duration of action of lidocaine (local anesthetic)?

Duration of Action of Lidocaine

Lidocaine typically has a duration of action of 90-200 minutes when used as a local anesthetic, with its half-life being approximately 100 minutes for infusions lasting less than 12 hours. 1

Pharmacokinetics of Lidocaine

Lidocaine's duration of action depends on several key factors:

• Route of administration: Different administration routes result in varying blood levels and durations of effect

  • Highest blood levels: Intercostal nerve block
  • Lowest blood levels: Subcutaneous administration 2

• Concentration and formulation:

  • Standard concentrations range from 0.5% to 2%
  • Duration increases with concentration and total dose 1

• Use of vasoconstrictors:

  • With epinephrine: 90-200 minutes
  • Without epinephrine: Shorter duration due to faster vascular absorption 1

• Site of administration: Areas with high vascularity lead to faster absorption and shorter duration 1

Metabolism and Elimination

Lidocaine follows a predictable metabolic pathway:

• Rapidly metabolized by the liver through oxidative N-dealkylation, ring hydroxylation, and amide linkage cleavage 2
• Approximately 90% is excreted as various metabolites
• Less than 10% is excreted unchanged 2
• Elimination half-life following IV bolus: 1.5-2 hours 2
• For infusions lasting >12 hours: Pharmacokinetics become non-linear, with half-life potentially extending to 3.22 hours 1

Duration Based on Administration Method

1. Infiltration anesthesia:

   • Duration: 90-200 minutes (with epinephrine)
   • Onset: Within 2-5 minutes 1

2. Topical application:

   • Significant anesthesia without occlusion: 25-30 minutes
   • Optimal effects: 35-40 minutes after application
   • Duration varies by formulation 3

3. Intravenous administration:

   • Half-life: 100 minutes for infusions <12 hours
   • For infusions >24 hours: Half-life increases to approximately 3.22 hours 1

Factors Affecting Duration

Several factors can significantly alter how quickly lidocaine wears off:

• Hepatic function: Liver dysfunction may prolong half-life two-fold or more 2
• Patient age: Elderly patients may experience longer duration due to decreased clearance
• Body weight: Dosing should be based on ideal body weight rather than actual body weight 1
• Drug interactions: Beta-blockers and amiodarone may reduce lidocaine metabolism and clearance 1
• Acid-base status: Acidemia increases free lidocaine concentration by reducing protein binding 1

Clinical Considerations

When using lidocaine, be aware of:

• After nerve blocks or fascial plane blocks, wait at least 4 hours before starting IV lidocaine infusion 1
• After IV lidocaine infusion, wait at least 4 hours before performing nerve or fascial plane blocks 1
• For prolonged infusions (>24 hours), consider reducing the infusion rate by approximately 50% even in patients without cardiac or hepatic failure 1

Safety Considerations

To ensure safe use:

• Monitor for early signs of toxicity: circumoral numbness, facial tingling, light-headedness, and tinnitus 4
• Severe toxicity can progress to cardiac arrhythmias, myocardial depression, seizures, and respiratory arrest 4
• Plasma concentrations above 5 μg/ml are associated with increased risk of toxicity 1
• Calculate maximum safe dose based on patient weight (4.4 mg/kg without epinephrine, 7 mg/kg with epinephrine) 1

By understanding these factors affecting lidocaine's duration of action, clinicians can better plan procedures and manage patient expectations regarding the timeline of anesthetic effects.