ALKALINIZATION OF LIDOCAINE
ALKALINIZATION OF LIDOCAINE — why add sodium bicarbonate?
Commercial lidocaine solutions are relatively acidic, particularly when epinephrine is added. This improves drug stability—but can make injection more painful and may slow onset.
🧪 The chemistry
Lidocaine is a weak base (pKa ≈ 7.9) and exists as:
BH⁺ (ionized) ⇌ B (unionized)
Only the unionized form readily crosses the lipid nerve membrane.
Adding sodium bicarbonate raises the solution pH:
↑ pH → ↑ unionized lidocaine → faster membrane penetration
Once inside the axon, lidocaine re-equilibrates, and the ionized form binds the intracellular voltage-gated Na⁺ channel, producing conduction blockade.
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💉 Why buffer lidocaine?
Alkalinization may provide:
↓ Pain on injection
Faster onset of neural blockade
Potentially improved block quality in some settings
A commonly used clinical mixture is approximately:
1 mL of 8.4% NaHCO₃ + 10 mL lidocaine
Exact preparation should follow local pharmacy/institutional protocols, particularly when other additives are present.
⚠️ Don't over-alkalinize
Increasing pH too far can cause precipitation of the local anesthetic, especially with some other local anesthetics.
So:
More bicarbonate ≠ better block.
🧠Postgraduate Pearl
Remember the sequence:
NaHCO₃ → ↑ pH → ↓ ionization → ↑ unionized fraction → ↑ nerve penetration → potentially faster onset
But the pharmacologically active form inside the nerve is predominantly the charged form binding the Na⁺ channel.
🎯 Take-home message
ALKALINIZATION helps lidocaine GET INTO the nerve; RE-IONIZATION helps it BLOCK the Na⁺ channel.
#Lidocaine #LocalAnesthetics #SodiumBicarbonate #RegionalAnesthesia #AnesthesiaPharmacology #NerveBlock #Anesthesiology #MedEducation
