By Rania Gollakner, BS, DVM, MPH

What is rifampin?

Rifampin (brand name: Rifadin®) is an antimicrobial medication that is primarily used to treat bacterial infections, although it can also help treat fungal and viral infections as well. It is most commonly used to treat a certain infection in horses, but it has also been used occasionally to treat specific types of infections in dogs and cats.

Its use in cats and dogs to treat infections is 'off label' or 'extra label'. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

How is rifampin given?

Rifampin is given by mouth in the form of a capsule or a compounded liquid suspension, on an empty stomach. However, if vomiting occurs, try giving the medication with food to see if it helps. This medication will take effect quickly, in about 1 to 2 hours, but its effects may not be visibly noticeable for a few days.

Shake compounded liquid forms of this medicine well before each use and measure each dose carefully.

Because this medication will stain anything it touches to an orange or red color, consider wearing gloves when administering the medication.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effects in dogs include vomiting, reduced appetite, and lethargy. Elevated liver enzymes may be observed when your veterinarian does blood work. Liver toxicity is also possible, and may be more common in dogs than other animals. Signs of liver toxicity include yellowing of the eyes, skin, or gums, vomiting (that continues), severe or bloody diarrhea, painful abdomen (stomach), or changes in behavior. In cats, liver dysfunction (abnormal or impaired function of the liver) can occur and can cause reduced appetite, vomiting, or yellowing of the skin or eyes. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

This medication can also cause a change in the color of urine, tears, and saliva to a red/orange color. It is an expected side effect, but it can stain fabrics.

Are there any risk factors for this medication?

Rifampin should not be used in pets that are allergic to it. It should be used with caution in pets with known liver dysfunction, or in pets that are pregnant or nursing. Rifampin should be used with caution in geriatric pets, as liver dysfunction may be more common.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when used in conjunction with rifampin: acetaminophen, isoniazid, fluoroquinolones, ifosfamide, amiodarone, azole antifungals, barbiturates, benzodiazepines, beta blockers, buspirone, chloramphenicol, clarithromycin, corticosteroids, cyclosporine, enalapril, dapsone, diltiazem, doxorubicin, fluoroquinolones, mycophenolate, opioids, praziquantel, quinidine, sertraline, theophylline, vincristine, and warfarin.

This medication can cause serious drug reactions, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Your pet should be monitored for side effects associated with liver toxicity. Your veterinarian may measure your pet’s liver function prior to starting the medication and again 10-14 days after the medication is started. If your veterinarian has prescribed long-term use of rifampin, liver function tests may be measured monthly until treatment is complete. Your veterinarian may also monitor your pet to be sure that the medication is working.

How do I store rifampin?

Rifampin should be stored away from light in a tight container, at room temperature between 15°C to 30°C (59°F to 86°F).

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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