Earlier work showed that some common mixtures of local anaesthetics and adjuvants form microscopic crystals. This laboratory study, published in Regional Anesthesia and Pain Medicine on 5 October 2026, measured eight such mixtures by liquid chromatography for 800 minutes after mixing and analysed the precipitate in lidocaine with bicarbonate, and lidocaine with ropivacaine and bicarbonate.
The concentration of local anaesthetic in solution stayed constant throughout, so crystal formation did not measurably reduce the dose in the syringe. The precipitates were made of pure local anaesthetic.
This is bench work and says nothing about what crystals do in tissue or near a nerve. It does narrow the question: the concern is not loss of potency, but whether injecting particles matters, which needs in vivo study. In the meantime, it is reasonable to prepare mixtures close to use and to inspect them.
- Prepare local anaesthetic and bicarbonate mixtures close to the time of injection
- Inspect mixtures for cloudiness or particles before injecting
- Do not assume a crystallised mixture has lost potency; concentration held in this study
- Avoid unnecessary admixtures where a single agent will do
Why it matters
It shifts the crystallisation question from potency to the unknown effect of particles in tissue.
Don't overread it
A laboratory study; it does not show crystals are harmless when injected.
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