Lidocaine for Horses: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Lidocaine is a prescription medication your vet may use in horses as a local anesthetic and, in some situations, as an intravenous antiarrhythmic or gastrointestinal support drug. It works by blocking sodium channels, which reduces nerve conduction. In practical terms, that means it can numb tissue for procedures and can also help stabilize certain abnormal heart rhythms.

In equine medicine, lidocaine is most commonly used for local infiltration, regional nerve blocks, and some ophthalmic or surgical blocks. Merck Veterinary Manual also notes that it is used in horses for ventricular tachycardia and is commonly used as an adjunct in colic surgery because of its potential to reduce postoperative ileus. That said, its GI benefits are not guaranteed in every case, and your vet will decide whether it fits your horse's situation.

Because lidocaine can affect the nervous system and cardiovascular system when absorbed systemically or given IV, it is not a medication pet parents should administer on their own unless your vet has specifically instructed you how and when to do so. Route matters. A dose that is appropriate for a nerve block is not the same as an IV infusion dose.

Your vet may use lidocaine in horses for several very different reasons. One common use is local or regional anesthesia for laceration repair, eye procedures, dental or facial nerve blocks, limb work, and other standing procedures. For example, Merck notes that 1-2 mL is often enough for an auriculopalpebral or supraorbital block, while larger orbital blocks for enucleation in horses may require 10-20 mL for a Peterson block or 5-10 mL per site for a 4-point block.

Lidocaine may also be used intravenously for ventricular tachycardia, a potentially serious abnormal heart rhythm. In that setting, it is used in the hospital where heart rhythm, blood pressure, and neurologic status can be monitored closely. It is not useful for supraventricular arrhythmias.

A third use is as an adjunctive IV infusion in some horses with postoperative ileus or proximal duodenitis-jejunitis, especially after abdominal surgery. Merck states that evidence for this use is conflicting, even though many horses that respond do so within about 12 hours of starting an infusion. That is why your vet may discuss lidocaine as one option rather than the only option.

Lidocaine dosing in horses depends completely on why it is being used, where it is being given, and how sick the horse is. There is no one-size-fits-all dose. For ventricular tachycardia, Merck lists a typical equine dose of 1.3 mg/kg IV over 5 minutes, followed by a constant-rate infusion of 0.05 mg/kg/min. An alternative approach listed by Merck is 0.25-0.5 mg/kg slow IV, repeated every 5-10 minutes as needed. These are hospital-level doses that require monitoring.

For local and regional anesthesia, your vet calculates the total volume and concentration based on the horse's weight, the site being blocked, and the procedure. In equine eye work, Merck notes that 1-2 mL may be enough for an auriculopalpebral or supraorbital block, while larger retrobulbar or orbital techniques use substantially more volume. The exact concentration, dilution, and maximum total dose should always come from your vet.

For ileus support, protocols vary by hospital, and published recommendations are not perfectly consistent. Because the evidence is mixed and toxicity can occur if the infusion rate is too high or the horse clears the drug poorly, your vet will usually use lidocaine only with careful IV pump control and ongoing reassessment. Horses with liver disease, reduced hepatic blood flow, or significant cardiovascular compromise may need extra caution because lidocaine is extensively metabolized by the liver.

If your horse is receiving lidocaine at home after a procedure, follow your vet's instructions exactly. Do not substitute human topical products, patches, sprays, or gels unless your vet specifically says they are appropriate. Formulation errors and accidental overdosing are real risks.

See your vet immediately if your horse develops agitation, muscle tremors, weakness, collapse, seizures, marked sweating, or worsening abnormal heart signs while receiving lidocaine. These can be signs of toxicity or overly rapid IV administration.

In horses, Merck specifically warns that lidocaine may cause neurologic clinical signs, including tachycardia, excitation, agitation, sweating, and seizures, especially after rapid IV administration. More broadly, local anesthetics can also cause CNS depression, bradycardia, and decreased myocardial contractility when systemic toxicity occurs. With local blocks, there is also a risk of tissue trauma, local swelling, or accidental injection into the wrong structure.

Some side effects are more subtle. A horse may seem unusually dull, unsteady, or restless before more obvious toxicity appears. Risk may be higher when the horse has hepatic disease, poor perfusion, or reduced drug clearance. If lidocaine is being used around the eye, it should not be used as ongoing pain relief on the cornea because topical anesthetics can damage the corneal epithelium.

If you ever think a compounded mixture, infusion pump, or dose calculation may be wrong, contact your vet right away. With lidocaine, timing matters.

Lidocaine should be reviewed alongside every other medication, supplement, sedative, and infusion your horse is receiving. Merck notes that it should not be infused through the same catheter or line as other medications, which matters in hospitalized horses on multiple IV treatments.

Interaction concerns are often less about one dramatic forbidden pairing and more about stacked physiologic effects. Drugs that affect heart rhythm, blood pressure, liver blood flow, or central nervous system function can change how safely a horse tolerates lidocaine. Horses with hypokalemia may also respond less well when lidocaine is being used for ventricular arrhythmias.

Your vet may use lidocaine alongside other pain medications, sedatives, anesthetics, or colic treatments, but that does not mean the combination is casual. Monitoring is what makes these combinations safer. Be sure your vet knows if your horse is also receiving medications such as detomidine, xylazine, ketamine, butorphanol, flunixin meglumine, phenylbutazone, or digoxin, because the full treatment plan may affect dose selection and monitoring needs.

Also tell your vet if your horse has a history of liver disease, poor circulation, collapse episodes, seizures, or prior drug reactions. Those details can change whether lidocaine is a good fit at all.