What happens if I mix different LA preparations, eg lidocaine and levobupivacaine? How does this affect calculation of the maximum dose?
Mixing of LAs is not recommended by the pharmaceutical industry but is a standard technique for some clinicians. Most preparations are miscible as the pH of the solutions is similar.
The theory behind the mixing of LA solutions is that one gets the benefits of both drugs (eg rapid onset of lidocaine and the prolonged duration of levobupivacaine). Conversely, it could be argued that the resulting solution is a diluted mixture of both drugs, containing half the concentration of each (if mixed to equal volumes). This may be true but there is surprisingly little evidence supporting or refuting either of these arguments. We believe the answer comes down to clinical preference.
What must be remembered is that each LA in the mixture acts on allexcitable membranes so an excess may result in toxic effects (see below). If mixing LAs, we recommend that the safest practice is not to exceed 100% of the combined maximum dose. For example, 10ml of lidocaine 1% contains 100mg of drug, ie 50% of the maximum dose for a 50kg patient. Furthermore, 10ml of 2.5mg/ml levobupivacaine would represent 25% of the maximum in the same patient. Using a 20ml mixture of the two would mean that the solution contains 75% of the maximum and should therefore be safe. However, 40ml of the same mixture would be 150% of the recommended maximum and may result in toxicity. If either of the solutions chosen contains adrenaline, then this increases the maximum dose for lidocaine, meaning a larger volume can be used.
全文请搜索 Ann R Coll Surg Engl. 2012 Mar; 94(2): 76–80.
doi: 10.1308/003588412X13171221502185
PMCID: PMC3954146
PMID: 22391358
Local anaesthetics
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