Professional reference. Follow your organisation’s protocol, product information and aseptic technique standards. This is not a substitute for local policy.
Quick reference
- Ratio: 1 mL sodium bicarbonate 8.4% : 10 mL lidocaine (1% or 2%, plain or with adrenaline).
- Small volumes: 0.1 mL bicarbonate per 1 mL lidocaine (e.g. 0.3 mL into a 3 mL syringe).
- Don’t buffer bupivacaine beyond tiny amounts or ropivacaine: they precipitate.
Why buffer lidocaine?
Lidocaine hydrochloride solutions are acidic (pH about 6–6.5 for plain lidocaine and about 3.5–5.5 for solutions with adrenaline, which are acidified to stabilise the adrenaline). Acidic solutions sting on injection. Local anaesthetics also work in their un-ionised (base) form, which crosses nerve membranes; at a pH closer to 7, a larger fraction is un-ionised, so onset can be faster. A meta-analysis of randomised trials found that adding bicarbonate significantly reduced injection pain, with the largest effect for solutions containing adrenaline.
Mixing ratios
| Local anaesthetic |
Volume |
Sodium bicarbonate 8.4% |
Comment |
| Lidocaine 1% or 2% |
10 mL |
1 mL |
Standard 10:1 |
| Lidocaine 1% or 2% with adrenaline |
10 mL |
1 mL |
Adrenaline degrades faster once buffered |
| Lidocaine (any) |
3 mL syringe |
0.3 mL |
Use a 1 mL syringe to measure bicarbonate |
| Lidocaine (any) |
20 mL |
2 mL |
Scale linearly |
| Bupivacaine 0.25–0.5% |
10 mL |
About 0.1 mL at most |
Precipitates readily; many protocols don’t buffer |
| Ropivacaine |
— |
Not recommended |
Precipitates above about pH 6 |
Sodium bicarbonate 4.2% (0.5 mEq/mL) is used in some paediatric settings; with 4.2%, use about double the volume, or follow your protocol.
Preparation step by step
- Check both products: name, strength, expiry, and that the lidocaine is suitable for the procedure (with or without adrenaline).
- Use aseptic technique: clean vial tops with alcohol and let them dry.
- Draw up the bicarbonate first into the syringe with a separate needle or filter needle, then draw up the lidocaine (or add bicarbonate to a lidocaine vial if your protocol uses multi-dose preparation).
- Mix gently by inversion.
- Inspect: the solution should be clear and colourless. Discard if cloudy or if particles appear.
- Label with “buffered lidocaine”, concentrations, time of preparation, and your initials.
- Change to the injection needle (for example 27–30 G), and inject slowly; warming to body temperature further reduces pain.
Stability and storage
Buffered solutions are less stable than the commercial products. Published studies suggest buffered plain lidocaine keeps its potency for some time when refrigerated, while adrenaline in buffered lidocaine-with-adrenaline degrades more quickly, reducing its vasoconstrictor effect. Because practice varies, many organisations require buffered lidocaine to be prepared immediately before use, or allow pharmacy-prepared batches with a defined short expiry. Follow your local policy; don’t store bedside preparations.
Safety reminders
- Buffering doesn’t change maximum doses: lidocaine about 4.5 mg/kg (max 300 mg) plain, 7 mg/kg (max 500 mg) with adrenaline, per product information.
- Aspirate before injecting to avoid intravascular injection.
- Know the signs of local anaesthetic systemic toxicity (perioral tingling, tinnitus, confusion, seizures, arrhythmias) and where lipid emulsion is kept.
- Don’t add bicarbonate to multi-dose vials unless your protocol and labelling allow it.
Related professional notes: clinical pharmacy notes and mixing drugs in one syringe.
Frequently asked questions
What is “buffered lidocaine”?
Lidocaine to which a small volume of sodium bicarbonate has been added to bring the pH closer to neutral, reducing injection pain. Some pharmacies supply it pre-mixed for clinics.
Can I buy lidocaine injection over the counter?
No. Injectable lidocaine is prescription-only. Topical lidocaine creams, patches and sprays are available without prescription in many countries.
Does buffering make lidocaine work longer?
Not reliably. Its main benefits are less injection pain and possibly faster onset. Duration depends mainly on the dose and on whether adrenaline is included.
Sources and further reading
CanforaMedicine Guide
