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Enrofloxacin (Baytril)
Revised: May 20, 2024
Published: January 01, 2001

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Baytril, Zobuxa, Enroquin, Enrosite

Available in 22.7 mg, 68 mg, and 136 mg tablets


Photo of a cat stretching on its side in the sun
Note the concerns about retinal damage and watch your cat for dilated pupils, bumping into things, misjudging jumping distances or other signs of vision loss. Image courtesy of Karen James.

Until sulfa drugs came on the scene in the 1940s, our efforts to combat bacterial infection were largely ineffective. As different antibiotics were developed, different types of bacteria were conquered, yet one bacterial species remained seemingly invincible: Pseudomonas aeruginosa. Eventually, antibiotics (the aminoglycoside class) were developed that could kill Pseudomonas, but they were available only as injectable products, and they had the potential to cause significant kidney damage if used too long. With these kinds of side effects and the ability to treat Pseudomonas limited to hospitalized patients (where injections could be given regularly), the battle with Pseudomonas was far from won.

A major breakthrough was the development of the fluoroquinolone class of antibiotics (including enrofloxacin, its counterpart for human use ciprofloxacin, and several others). These medications are active against many bacterial types, including Pseudomonas. They are available as tablets and are not associated with the serious side effects that plague the aminoglycoside group.

Fluoroquinolones act by deactivating bacterial enzymes needed for the transcription of DNA. DNA is tightly coiled in order to fit inside a cell. Segments to be used must be uncoiled by an enzyme called DNA gyrase. The fluoroquinolone antibiotic deactivates DNA gyrase, making the reading of DNA impossible. The bacterial cell dies. DNA gyrase from species other than bacteria is of a completely different shape and remains untouched.

How this Medication is Used

This medication may be used in either dogs or cats to combat different types of infections, especially those involving Pseudomonas. Enrofloxacin is also active against Staphylococci and thus is commonly used for skin infections. However, it is not helpful against anaerobic infections and is commonly used in combination with other antibiotics for a boost in function. 

Enrofloxacin is best given on an empty stomach, but if nausea becomes an issue, it can be given with food. It is usually given either once or twice daily as a tablet. Tablets come as chewable or enteric-coated. The coated tablets should not be crushed as they taste bitter, and releasing this flavor is likely to lead to rejecting the tablet.

Side Effects

Side effects are of two types: common and severe. Common side effects have a reasonable likelihood of occurring, so it is helpful to know about them. Severe side effects are generally rare, but because of their large consequences, you should also know about them. Nausea is most commonly a problem when higher doses of enrofloxacin are used, as might be used in treatment of a confirmed Pseudomonas infection.

Common side effects of enrofloxacin are upset stomach, as can be seen with any oral medication. In most cases, this would be vomiting or appetite loss; giving the medication with food should save the problem. 

Enrofloxacin can produce crystals in the urine, especially if the patient is dehydrated. These crystals may show up on a laboratory test thus it is important to be aware of this. Enrofloxacin crystals should not be confused with more clinically relevant struvite, oxalate, or urate crystals.

Severe side effects

  • In immature dogs (less than eight months of age in small or medium dog breeds, older in larger breeds), damage to joint cartilage can occur. This phenomenon is only seen in growing dogs and does not seem to be a problem in cats. It is preferable not to use this in puppies unless the severity of the infection warrants it.

  • In infections with Strep. Canis, a drug interaction can occur between enrofloxacin and the bacteria that leads to necrotizing fasciitis (flesh-eating disease) where large areas of tissue die. Other quinolone class antibiotics do not carry this side effect, so if Strep. canis cannot be ruled out, it may be better to choose another antibiotic.

  • Retinal damage (dilated pupils and blindness) in cats can occur in higher doses (see below).

Interactions with Other Drugs

Sucralfate (a medication used to treat stomach ulcers) may bind enrofloxacin and prevent it from entering the body. These medications should be given at least 2 hours apart if they are used together.

Theophylline (an airway dilator) blood levels may be higher than usual if this medication is used concurrently with enrofloxacin. The dose of theophylline may need to be reduced.

If enrofloxacin is used with oral cyclosporine (an immunosuppressive medication used for inflammatory bowel disease), the kidney-damaging properties of cyclosporine may become worse.

Medications or supplements containing iron, zinc, calcium, magnesium, or aluminum will bind enrofloxacin and prevent absorption. Give such medications at least 2 hours apart from the enrofloxacin. For this reason, cheese is not a good treat in which to hide enrofloxacin.

Enrofloxacin synergizes with numerous other antibiotics, which means the effects of the two antibiotics together are greater than expected. This phenomenon adds a boost to treating infections of many types.

Concerns and Cautions

Enrofloxacin is best not given with cheese or other high-calcium foods.

Pseudomonas infections are especially common in the ears. In this location, especially high doses of enrofloxacin are needed to clear this infection. Expect to give a lot of pills and be prepared for expenses.

Enrofloxacin has toxic properties in humans. It is for veterinary use only.

Enrofloxacin should not be used in pregnant or nursing pets or in immature dogs unless the severity of the infection warrants it.

Enrofloxacin may lower the seizure threshold (meaning that it can make it easier to have seizures). This is not a problem for normal animals, but fluoroquinolones are best not used in animals with known seizure disorders

Dose adjustments may be needed for patients with kidney or liver disease.

Retinal damage has been seen in cats when higher doses, such as might be used to treat a Pseudomonas ear infection, are used. This reaction is not common even with very high doses, but there is no way to predict which cats will react. Blindness, temporary or permanent, can result. Kidney disease predisposes a cat to retinal damage from enrofloxacin. 

Enrofloxacin can produce crystals in urine.

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