Analgesia

Lidocaine CRI

Adjunctive systemic analgesia CRI in dogs. Useful perioperatively, for severe medical pain (pancreatitis, peritonitis), for post-operative ileus, and as adjunctive therapy in GDV and septic peritonitis. Also the L in the MLK multimodal CRI. Dog-only: cats are uniquely sensitive to lidocaine cardiotoxicity at analgesic doses.

Stock: 20 mg/mL (2% lidocaine, plain)

Use 2% lidocaine WITHOUT epinephrine. Lidocaine-with-epinephrine (sold for dental and local infiltration) looks similar on the shelf, giving it IV would deliver an unintended epinephrine bolus. Do NOT use the product containing epinephrine IV. Always read the label twice.
Dog-only. Most clinicians avoid IV lidocaine in cats for anesthetic or analgesic purposes. Cats are markedly more sensitive to both CNS and cardiodepressant effects, and lidocaine added to isoflurane in cats causes greater cardiovascular depression than equipotent isoflurane alone.
Toxicity monitoring. Watch for muscle twitching, ataxia, nystagmus, drowsiness, vomiting, seizures, hypotension. Therapeutic plasma 1–6 µg/mL; toxicity likely above 8 µg/mL. Antidote: IV lipid emulsion 20% can be beneficial. Reduce doses 30–50% in patients with hepatic dysfunction.

Lidocaine analgesic CRI doses (dogs)

Loading dose: 1–2 mg/kg IV slowly (over 2–4 minutes; rapid bolus risks dose-dependent hypotension)
Standard maintenance CRI: 25–50 µg/kg/min (= 1.5–3 mg/kg/hr) for lidocaine alone or in MLK
GDV / septic peritonitis: 17–50 µg/kg/min (= 1–3 mg/kg/hr), maintain at least 3 hr postoperatively
Higher published combos (surgical only): up to 100 µg/kg/min (= 6 mg/kg/hr) in lidocaine/dexmed/ketamine; step down postoperatively

Species

Dog (only)

Cat is intentionally not selectable, see banner above.

Patient weight

lb kg

Maintenance dose

mg/kg/hr µg/kg/min

Doses are commonly published in both conventions; switch the unit to match how your protocol is written. Standard range: 1.5–3 mg/kg/hr = 25–50 µg/kg/min. Default 2.5 mg/kg/hr.

Awaiting input

Enter a patient weight to see the result.

Reference

How the calculation works

Lidocaine stock is 20 mg/mL (2%). The dose is entered in mg/kg/hr or µg/kg/min, both are equivalent; the calculator always shows both. Converting mg/kg/hr to a pump rate:

$$\text{mL/hr} = \frac{\text{weight}_{\text{kg}} \times \text{dose}_{\text{mg/kg/hr}}}{\text{stock}_{\text{mg/mL}}}$$

To convert µg/kg/min to mg/kg/hr:

$$\text{mg/kg/hr} = \frac{\text{dose}_{\mu g/kg/min} \times 60}{1000}$$

Worked example with current inputs

Enter a patient weight to see the worked example.

Rationale

Why this calculator is dog-only

Cats are markedly more sensitive to the CNS and cardiodepressant effects of lidocaine than dogs. Most clinicians avoid IV lidocaine in cats for analgesic or anesthetic purposes; when added to isoflurane in cats, lidocaine causes greater cardiovascular depression than an equipotent dose of isoflurane alone, and so is not recommended as part of a balanced feline anesthesia protocol. The published maintenance CRI applies to dogs only. No feline maintenance dose has been validated. The same rationale applies to MLK, which InfusionFox also locks to dogs. For feline analgesia, consider single-drug fentanyl (/fentanyl), buprenorphine, or hydromorphone.

Indications and benefits

Beyond systemic analgesia, lidocaine CRI provides an antihyperalgesic effect (reducing wind-up sensitization), ≈30% MAC sparing in dogs, and reactive oxygen species (ROS) scavenging effects relevant to GDV. A survival benefit has been documented in dogs undergoing laparotomy for septic peritonitis when lidocaine (50 µg/kg/min) is added to opioid analgesia. Lidocaine is one of the three components of the MLK multimodal CRI; if the patient also needs morphine and ketamine analgesia, see /mlk for the published fixed-recipe protocol.

Toxicity

Therapeutic plasma range is 1–6 µg/mL; toxicity becomes likely above 8 µg/mL. Lethal dose in dogs is estimated at 16–28 mg/kg. Signs include ataxia, nystagmus, drowsiness, depression, muscle tremors, nausea/vomiting, seizures, bradycardia, hypotension, and at very high concentrations circulatory collapse. IV lipid emulsion 20% can be beneficial for treating lidocaine toxicity. Cessation of therapy or rate reduction is sufficient for minor signs; benzodiazepines for seizures; supportive treatment for circulatory depression. Reduce doses 30–50% in patients with hepatic dysfunction. Concurrent cimetidine or beta-blocker therapy increases lidocaine concentration and toxicity risk.

Stepping down

For combined-agent protocols (eg MLK), discontinue lidocaine and ketamine first. For single-agent lidocaine CRI, taper or discontinue based on pain assessment; re-load with a 1–2 mg/kg IV bolus if breakthrough pain occurs. Plumb's notes that prolonged infusions can lead to progressive accumulation of lidocaine and metabolites; dosage modification may be required.

Sources

Primary: Plumb's Veterinary Drugs, lidocaine (intravenous; systemic) monograph (current edition). Sections used: Prescriber Highlights, Uses/Indications, Pharmacology/Actions, Pharmacokinetics, Contraindications/Precautions/Warnings, Adverse Effects, Overdose/Acute Toxicity, Drug Interactions, Dosages (dogs), Compatibility/Compounding Considerations.
Secondary: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. St. Louis, MO: Elsevier; 2023. Chapter 134 (Analgesia and Constant Rate Infusions), Table 134.1 (Commonly Used Analgesic Agents), p. 789.