About the lidocaine dose calculator
This calculator performs the standard weight-based arithmetic used to estimate a maximum lidocaine dose: multiply patient weight by a maximum milligrams-per-kilogram figure, cap the result at a fixed absolute ceiling, then convert that milligram limit into a volume using the chosen percent concentration. It is intended for educational and planning use, not as a substitute for a clinician's dosing decision, package insert, or institutional protocol.
The formula, step by step
Percent concentration is grams per 100 mL, so multiplying the percentage by 10 gives milligrams per mL: a 1% solution is 10 mg/mL, a 2% solution is 20 mg/mL, and a 4% solution is 40 mg/mL. The weight-based maximum dose is patient weight in kilograms multiplied by a maximum mg/kg figure, commonly cited as approximately 4.5 mg/kg for plain (epinephrine-free) lidocaine and approximately 7 mg/kg when epinephrine is co-administered, since epinephrine slows systemic absorption. That weight-based figure is then capped at a commonly cited absolute maximum, often around 300 mg plain and 500 mg with epinephrine, because very large patients should not receive unlimited total drug. Dividing the final milligram limit by the mg/mL concentration gives the maximum volume in mL. A planned dose is then checked against that limit by multiplying the planned volume by the concentration and comparing it to the weight-based maximum.
Why the inputs matter
- Different published references (package inserts, pharmacology texts, specialty society guidance) cite mg/kg and absolute-maximum figures that vary somewhat by a point or two — always confirm the specific limit your institution or product labeling uses before relying on a number.
- Epinephrine changes the safe ceiling because it constricts local blood vessels and slows systemic uptake, which is why the with-epinephrine limit is higher than the plain limit.
- Concentration and volume are easy to mix up: doubling the percent concentration doubles the milligrams delivered for the same volume, so always re-check the mg/mL figure before drawing up a dose.
Important disclaimer
This tool does not constitute medical advice and does not replace a licensed clinician's judgment. Do not use it to determine an actual patient dose without confirming the limit against current prescribing information and your institution's protocol.