Bute (Phenylbutazone) for Horses

PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.

What Is Bute Used for in Horses?

Short for phenylbutazone, Bute is a non-steroidal anti-inflammatory (NSAID) prescription medication FDA-approved for use in horses to treat inflammatory conditions associated with the musculoskeletal system. 

Many different formulations of this product are available, including tablets, injectable, powder, and paste. It’s important to note which product you are using and refer to the product label for additional information.

The use of this medication is prohibited in lactating dairy cattle and animals intended for human consumption.

Bute is also available under the brand names Equizone, Phenylbute, Butatron, and Butequine.

Compounded Bute for Horses

In certain circumstances, your veterinarian may recommend a compounded formulation of bute.

Compounded medications are prescribed if there’s a specific reason your animal’s health can’t be managed by an FDA-approved drug, such as if your animal has trouble taking pills in capsule form, the dosage strength is not commercially available, or the animal is allergic to an ingredient in the FDA-approved medication.

Compounded medications are not FDA-approved. They’re created by either a veterinarian or a licensed pharmacist on an individual basis to best suit an animal’s particular needs.

Your veterinarian will determine whether a compounded medication is right for your horse.

How Bute Works in Horses

As a non-selective NSAID, Bute blocks the body’s COX- 2 pathway, which lowers the production of natural chemicals that trigger inflammation, thereby reducing fever and offering pain relief.

Due to its non-selective property, Bute also blocks the COX-1 pathway, which can cause the major side effects associated with digestion, kidney health, and clotting.

Bute for Horses Directions

Because there are many formulations of Bute, it’s important to closely follow the directions on the drug label or as provided by your veterinarian.

Your veterinarian will determine the appropriate dosage based the animal’s weight, condition, and other medications they may be prescribed.

When given by mouth, Bute is usually given once or twice daily with food.

Note: When administering oral paste, your animal’s mouth should be empty.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of phenylbutazone.

Generally, they may instruct you to give it when you remember, or, if it is almost time for your pet’s next dose, to skip the missed dose and resume your normal dosing schedule.

Do not give extra or double doses.

Possible Side Effects of Bute in Horses

Bute is generally well-tolerated in horses. Possible side effects include:

• Mouth or stomach ulcers

• Right dorsal colitis, which can present as diarrhea, dehydration, lethargy, decreased appetite, dark mucus membranes, and/or increased heart rate

• Kidney disease

• Diarrhea

• Black or tarry manure

• Loss of appetite

• Hypoproteinemia (low blood protein levels), which can present as weight loss or swelling of the limbs (edema)

When this medication is given as an injection, swelling, inflammation, and wound formation at the injection site is possible.

Stop administering Bute at the first sign of gastrointestinal upset, jaundice, or blood dyscrasia (abnormal condition or disease of the blood) and speak with your veterinarian.

If you believe your pet may be experiencing any other side effects, consult your veterinarian.

Human Side Effects

Bute is not approved for use in humans.

If you accidentally ingest this medication, call your physician or the national Poison Control Center hotline at 800-222-1222.

Monitoring Your Horse

While no specific monitoring is required for this medication, your veterinarian may recommend routine testing depending on your pet’s individual needs, other medications they may be on, and/or the issue that initially caused your pet to be placed on this medication.

For example, to guard against agranulocytosis (low white blood cell count), your veterinarian may recommend conducting routine blood counts at weekly intervals during the early phase of therapy and at intervals of two weeks thereafter.

If your horse needs to be on an NSAID long-term, your veterinarian may wish to discuss alternative medication options or the use of digestive system protective medications while on this medication.

When To Call Your Vet

Call your veterinarian if any of the following apply:

• Severe side effects are seen (see above)

• Your animal's condition worsens or does not improve with treatment

• You see or suspect an overdose

• You have additional questions or concerns about the use of Bute

Bute Overdose Concerns in Horses

The most common symptoms of an overdose in horses are:

• Colic

• Loss of appetite

• Stumbling/incoordination

• Depression

• Kidney disease

• Diarrhea/colitis

• Black or tarry manure

If you suspect an overdose or if a small animal gets into this medication, immediately contact your veterinarian, seek emergency veterinary care, or contact an animal poison control center. Consultation fees often apply.

• Pet Poison Helpline 855-764-7661 

• ASPCA Animal Poison Control 888-426-4435 

How To Store Bute for Horses

Keep the following storage tips in mind:

• Please see individual packaging for product-specific storage recommendations.

• Carefully dispose of used needles in accordance with all federal, state, and local environmental laws.

• Keep out of reach of children and pets.