Lidocaine Onset of Action
Lidocaine has a rapid onset of action of approximately 1 minute when used for local anesthesia. 1
Pharmacological Properties of Lidocaine
Lidocaine works by stabilizing the neuronal membrane through inhibition of ionic fluxes required for the initiation and conduction of impulses, thereby producing local anesthetic effects 2. As a local anesthetic, lidocaine offers several advantages:
- Fast onset of action (1 minute) compared to alternatives like diphenhydramine (5 minutes) 1
- Intermediate duration of action (60-120 minutes) without epinephrine 3
- Duration can be extended to 1-1.5 hours with the addition of epinephrine 2
Onset of Action in Different Applications
The onset of action for lidocaine varies slightly depending on the specific application:
- Local infiltration: ~1 minute 1
- Nerve blocks: 10-15 minutes 3
- Intravenous administration: Peak blood levels may occur as early as 5 minutes and as late as 30 minutes 2
Factors Affecting Onset of Action
Several factors can influence how quickly lidocaine takes effect:
- Addition of epinephrine: Prolongs duration but doesn't significantly alter onset time 4
- Concentration: Higher concentrations generally have faster onset
- pH of solution: Buffering lidocaine with sodium bicarbonate (1:9 or 1:10 ratio) can decrease injection pain and potentially speed onset 4
- Temperature: Warming the solution to approximately 40°C can improve patient comfort during injection 4
- Vascularity of injection site: More vascular areas may have faster onset due to increased blood flow
Comparison to Other Local Anesthetics
When comparing lidocaine to other local anesthetics:
- Lidocaine (1 minute onset) acts significantly faster than diphenhydramine (5 minutes onset) 1, 5
- Lidocaine (1.3 minutes) has faster onset than ropivacaine (4.5 minutes) 6
- Bupivacaine has a slower onset (20-30 minutes) but longer duration (240-360 minutes) 3
Safety Considerations
When using lidocaine, it's important to consider:
- Maximum safe dose: 7 mg/kg with epinephrine, 4.5 mg/kg without epinephrine for adults 1, 4
- Children: 3.0-4.5 mg/kg with epinephrine, 1.5-2.0 mg/kg without epinephrine 1, 4
- Signs of toxicity: Circumoral numbness, facial tingling, slurred speech, metallic taste, auditory changes, and hallucinations 1
- Avoid in patients with true lidocaine allergy (rare, representing only 1% of all adverse reactions) 1
Clinical Applications
The rapid onset of lidocaine makes it particularly useful for:
- Short diagnostic and surgical procedures 3
- Situations requiring immediate pain control
- Procedures where rapid onset is prioritized over duration of action
For longer procedures or when extended post-procedural analgesia is desired, consider:
- Adding epinephrine to prolong effect
- Using a longer-acting agent like bupivacaine
- Newer formulations like lidocaine/multivalent ion complexes that can extend duration to approximately 14 hours 7