Local Anesthetic Maximum Dose Calculator
Enter the patient weight, choose a local anesthetic and concentration, then toggle epinephrine on or off. The calculator returns the maximum safe dose in milligrams and the equivalent injection volume in millilitres, using published mg/kg limits and hard absolute caps. It also shows the expected onset and duration of action, plus patient-specific lipid rescue (Intralipid 20%) doses in case of local anesthetic systemic toxicity (LAST).
How local anesthetic maximum dose is calculated
The safe ceiling for any local anesthetic injection is set by two separate constraints that both apply simultaneously. The first is a weight-based limit expressed in milligrams per kilogram of body weight. The second is a hard absolute cap in milligrams that applies regardless of patient size. The calculator uses whichever is lower. To find the maximum volume to inject, the total milligram dose is divided by the concentration of the solution in milligrams per millilitre (a 1% solution is 10 mg/mL, a 2% solution is 20 mg/mL, and so on). For example, a 70 kg adult receiving plain lidocaine at the 4.5 mg/kg limit reaches 315 mg, but the hard cap is 300 mg, so the safe ceiling is 300 mg. At a 1% concentration that equals 30 mL.
Effect of epinephrine on dose and duration
Adding epinephrine (adrenaline) as a vasoconstrictor reduces the rate at which the local anesthetic is absorbed into the systemic circulation from the injection site. This lowers the peak plasma concentration reached for any given dose, which is the key driver of toxicity. As a result, published safe dose limits are higher when epinephrine is used: lidocaine rises from 4.5 to 7 mg/kg, bupivacaine from 2.5 to 3 mg/kg, mepivacaine from 4.5 to 6.6 mg/kg. Duration of action also increases substantially because the drug stays in the tissue longer. However, epinephrine is contraindicated in end-arterial locations (fingers, toes, ear lobes, the nose, and the penis) where vasoconstriction can cause ischaemia, and it is used with caution in patients with severe cardiovascular disease, hyperthyroidism, or who are taking MAO inhibitors.
Local anesthetic systemic toxicity (LAST) and lipid rescue
LAST occurs when local anesthetic enters the bloodstream in sufficient quantity to affect the central nervous system and the heart. Early CNS signs include perioral numbness, a metallic taste, lightheadedness, tinnitus, and agitation; these can progress rapidly to seizures and respiratory arrest. Cardiovascular signs include tachycardia and hypertension early, followed by bradycardia, ventricular arrhythmias, and potentially cardiac arrest. Bupivacaine is especially cardiotoxic because it binds sodium channels with high affinity and dissociates slowly. The primary emergency treatment is 20% Intralipid (lipid emulsion therapy): a bolus of 1.5 mL/kg IV over one minute, followed by an infusion of 0.25 mL/kg/min, with a maximum total volume of approximately 12 mL/kg. The bolus may be repeated once if the patient does not respond. Every location where regional anaesthesia or nerve blocks are performed should have Intralipid immediately to hand. The patient-specific doses shown by this calculator are derived from these ASRA 2020 guidelines.
Amide versus ester local anesthetics
Local anesthetics are divided into two chemical classes based on the bond that links the aromatic ring to the amine tail. Amides (lidocaine, bupivacaine, ropivacaine, mepivacaine, levobupivacaine, prilocaine) are metabolised in the liver, have a longer shelf life, and carry a very low allergy rate. Esters (chloroprocaine, procaine, tetracaine, benzocaine) are metabolised rapidly by plasma cholinesterase, which gives them a shorter duration; they also release para-aminobenzoic acid (PABA) as a metabolite, which accounts for the higher rate of true allergic reactions with this class. Patients who report an allergy to one ester can usually tolerate amides, and vice versa. When two amide agents are combined, their toxicities are additive, so combined doses should be compared against a shared ceiling rather than calculated separately.
Local anesthetic maximum dose reference
| Agent | Class | Plain (mg/kg) | With Epi (mg/kg) | Hard cap plain (mg) | Hard cap with epi (mg) | Duration plain (min) | Duration with epi (min) |
|---|---|---|---|---|---|---|---|
| Lidocaine | Amide | 4.5 | 7 | 300 | 500 | 90 | 210 |
| Bupivacaine | Amide | 2.5 | 3 | 175 | 225 | 180 | 360 |
| Ropivacaine | Amide | 3 | 4 | 225 | 300 | 210 | 360 |
| Mepivacaine | Amide | 4.5 | 6.6 | 400 | 550 | 90 | 180 |
| Levobupivacaine | Amide | 2 | 3 | 150 | 225 | 180 | 360 |
| Prilocaine | Amide | 5 | 8 | 400 | 600 | 90 | 150 |
| Chloroprocaine | Ester | 11 | 14 | 800 | 1000 | 45 | 75 |
Published mg/kg ceilings and hard absolute caps. Epinephrine increases both limits and duration. Values are for adults; use lean body weight in obese patients.
Frequently asked questions
Why does bupivacaine have such a low mg/kg limit?
Bupivacaine binds cardiac sodium channels much more avidly than lidocaine and dissociates very slowly, making its cardiotoxicity difficult to treat. Even small excesses can cause life-threatening ventricular arrhythmias, which is why the ceiling is kept at 2.5 mg/kg without epinephrine (175 mg absolute). Ropivacaine and levobupivacaine were developed as safer alternatives with similar long-acting profiles but reduced cardiac toxicity.
Should I use actual body weight or lean body weight?
For patients of normal build, actual body weight is appropriate. For obese patients, the American Society of Regional Anesthesia (ASRA) and several anaesthetic societies recommend lean body weight, because local anesthetics are not highly fat-soluble and dosing on actual weight can risk over-dosing. The BNF and UK Association of Anaesthetists recommend ideal body weight. Enter the weight you intend to dose against; the calculator applies the mg/kg limit to whatever value you enter.
Can I use this calculator for epidural or spinal dosing?
This calculator covers infiltration and peripheral nerve block dosing. Epidural and spinal routes involve different pharmacokinetics, much smaller volumes for intrathecal use, and different absolute limits. The maximum doses shown here are not directly applicable to neuraxial techniques and you should consult dedicated epidural or spinal dosing references for those routes.
What are the early warning signs of LAST?
The earliest signs are often neurological: tingling or numbness around the mouth, a metallic taste, ringing in the ears, dizziness, slurred speech, and unusual anxiety or restlessness. These can occur even without pain at the injection site. If any of these appear after a local anesthetic injection, stop dosing immediately, call for help, give oxygen, and prepare to treat seizures and cardiovascular collapse. Have 20% Intralipid within reach at all times.
Does concentration affect the maximum safe dose?
No, the maximum safe dose in milligrams is determined by body weight and the mg/kg limit, regardless of concentration. Concentration only affects the volume needed to deliver that dose. A higher concentration lets you use a smaller volume for the same dose, while a lower concentration increases the volume. The risk of toxicity is set by the total milligrams injected, not by the percentage on the vial.
Is adding epinephrine always better?
Adding epinephrine raises the safe dose ceiling and prolongs duration, which are genuine advantages for larger blocks. However, it is contraindicated in end-arterial sites (fingers, toes, nose, ear lobes, penis) where peripheral vasoconstriction can cause tissue ischaemia. Caution is also needed in patients with poorly controlled hypertension, severe heart disease, thyrotoxicosis, or those on non-selective beta-blockers, where even the small systemic absorption of epinephrine can cause cardiovascular effects.
What is 20% Intralipid and how does it work?
Intralipid is an intravenous fat emulsion originally used for parenteral nutrition. In the context of LAST, the "lipid sink" theory holds that the large lipid phase in the bloodstream sequesters the lipophilic local anesthetic molecules and rapidly lowers the free drug concentration available to bind cardiac and CNS receptors. It may also have direct metabolic effects on the heart. Every facility that performs nerve blocks should stock 500 mL of 20% Intralipid and have a clear protocol for its use.