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Cardiology

Lidocaine CRI · Antiarrhythmic

First-line CRI for sustained ventricular tachycardia, hemodynamically significant VPCs, and post-cardioversion VF prophylaxis in dogs. Limited and cautious use in cats given their markedly impaired clearance and increased toxicity sensitivity. Alternatives (sotalol, magnesium for refractory VT) are often preferred. Continuous ECG monitoring required. For the analgesic CRI indication in dogs (lower dose range, standalone or as part of MLK protocols), see /lidocaine.

Stock: 2% lidocaine (20 mg/mL, 20 000 µg/mL), 20 mL multi-dose vial (400 mg per vial)
How this calculator works

Enter the patient's weight, species, and the desired CRI dose. The calculator picks a concentration (20, 10, or 4 mg/mL) that keeps the pump in its accurate range.

Cat dosing is markedly different from dogs; published range is 10–40 µg/kg/min vs 25–80 in dogs, with a much lower caution threshold given the cat-specific clearance differences. The calculator enforces species-specific ranges automatically once species is selected.

Loading dose (2 mg/kg dogs, 0.25–0.75 mg/kg cats) is shown above the CRI maintenance rate. The species asymmetry in loading dose is real and must be respected; cat overdose can produce seizures, profound CNS depression, and cardiovascular collapse.

Dogs: 25.0–80.0 · Cats: 10.0–40.0 ug/kg/min
10000 µg/mL
Draw 25 mL of 2% stock and dilute with 25 mL of 0.9% NaCl or 5% dextrose into a 50 mL syringe (1:1 dilution)
Use a different concentration

All preparations are pharmacologically equivalent. The default (10000 µg/mL) fits the most common clinical use case. The alternatives below cover situational needs.

Awaiting input

Enter a patient weight to see the result.

Reference

How the calculation works

Lidocaine CRI · Antiarrhythmic is dosed in µg/kg/min. To convert a per-minute dose into a per-hour CRI rate, multiply by 60. The full formula:

$$\text{mL/hr} = \frac{\text{weight}_{\text{kg}} \times \text{dose}_{\mu g/kg/min} \times 60}{\text{concentration}_{\mu g/mL}}$$

Why the 60? The patient's weight (kg) times the dose (µg per kg per minute) gives micrograms per minute. Multiplying by 60 converts to micrograms per hour. Dividing by the concentration (µg per mL of the prepared CRI) yields mL per hour.

In target-pump-rate mode the pump rate is fixed by the clinician and the bag concentration is the unknown. The preparation runs in three steps.

Step 1: bag concentration

Same numerator as standard-bag mode (the total drug delivered per hour for this patient), but divided by the chosen pump rate instead of by a chosen bag concentration:

$$\text{bag concentration}_{\mu g/mL} = \frac{\text{weight}_{\text{kg}} \times \text{dose}_{\mu g/kg/min} \times 60}{\text{pump rate}_{\text{mL/hr}}}$$

Step 2: total drug in the bag

The bag concentration times the chosen bag volume gives the total micrograms of drug to add. Convert to milligrams (divide by 1,000) for the size of stock you'll actually be drawing:

$$\text{total drug}_{\mu g} = \text{bag concentration}_{\mu g/mL} \times \text{bag volume}_{\text{mL}}$$
$$\text{total drug}_{mg} = \frac{\text{total drug}_{\mu g}}{1{,}000}$$

Step 3: volume of stock to draw

Total drug divided by the stock vial concentration gives the volume of stock to draw and add to the bag:

$$\text{stock volume}_{\text{mL}} = \frac{\text{total drug}_{mg}}{\text{stock}_{mg/mL}}$$

Worked through together: divide the total drug in the bag by the stock vial's mg/mL to get the mL of stock that contains that much drug. That is the volume to pull into the syringe and add to the bag.

Worked example with current inputs

Enter a patient weight to see the worked example.

Reference

Recommended dilutions

Target concentration Dilution When useful
20000 µg/mL Use the 2% (20 mg/mL) stock directly in a 50 mL syringe via syringe pump; no dilution needed Direct use of stock for patients ≥15 kg. Lowest preparation effort; recommended when pump rate stays in the precision range without dilution.
10000 µg/mL Draw 25 mL of 2% stock and dilute with 25 mL of 0.9% NaCl or 5% dextrose into a 50 mL syringe (1:1 dilution) Standard 1:1 dilution for patients 3–15 kg. Matches typical syringe-pump workflow.
4000 µg/mL Draw 10 mL of 2% stock and dilute with 40 mL of 0.9% NaCl or 5% dextrose into a 50 mL syringe (1:4 dilution) Dilute preparation for cats and very small dogs (<3 kg). Essential when the cat-specific lower dose range would drop pump rate below 2 mL/hr on more concentrated preparations.

Stock: 2% lidocaine (20 mg/mL), 20 mL multi-dose vial = 400 mg per vial. For CRI: dilute in 0.9% NaCl or 5% dextrose (both compatible). Larger patients can run the 2% stock directly via syringe pump; smaller patients need progressive dilution to keep pump rate in the precision range. Use the PRESERVATIVE-FREE ("plain") 2% formulation, NOT lidocaine with epinephrine; the epinephrine-containing products are for local infiltration only and would produce unwanted systemic effects on IV infusion. Compatibility: lidocaine is compatible with most IV fluids and many co-administered drugs. Avoid mixing in the same line with sodium bicarbonate (precipitation risk in some concentrations).

Dilution helper — Lidocaine CRI · Antiarrhythmic

Work out how many mL of stock drug and diluent to combine for any target concentration. Stock is pre-filled for Lidocaine CRI · Antiarrhythmic; change it if you're using a different vial.

Suggestions from the reference table above
Draw up

Enter stock, target concentration, and final volume.