(for veterinary information only)


22.7 mg, 68 mg, and 136 mg


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 bbacterial 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 had 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.

Helix Model small

(Photocredit: NIH Public Image Library)

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 plagued the aminoglycoside group.

Fluoroquinolones act by deactivating bacterial enzymes necessary for the transcription of DNA. DNA is very 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. Mammalian DNA gyrase is of a completely different shape and remains unharmed.


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.


At approximately ten times the recommended dose vomiting and diarrhea may be seen with this medication. At normal doses, this should not be seen. Dogs with Pseudomonas ear infections require very high doses of enrofloxacin and nausea may indeed become a problem.

In immature dogs (less than 8 months of age) 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 medication in puppies unless the severity of the infection present warrants it.

The use of enrofloxacin can produce crystals in urine. These crystals may show up on a laboratory test thus it is important to be aware of this side effect. Enrofloxacin crystals should not be confused with more clinically relevant struvite, oxalate, or urate crystals.

See retinal damage below regarding the recently described feline retinal problem associated with enrofloxacin at higher doses.


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, magnesium or aluminum will bind enrofloxacin and prevent absorption into the body. Such medications should be separated from enrofloxacin by at least 2 hours.


Enrofloxacin tablets are enteric coated to hide the drug's naturally bitter taste. If the tablets are crushed for some reason, the bitter taste is more readily apparent. Crushing tablets to put in an animal's food is unlikely to be an effective way to administer enrofloxacin. Recently, Bayer has manufactured an alternative called a flavor-tab that is much more palatable than the purple-colored enteric coated tablets. The tan colored flavor-tabs are more easily crushed and mixed in food.

Pseudomonas infections are especially common in 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 expense.

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 facilitate seizures). This is not a problem for normal animals but fluoroquinolones are best not used in animals with known seizure disorders.

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. This reaction has only been reported with enrofloxacin and not with other fluoroquinolones, as it is theorized that the biochemical structure of enrofloxacin leads to especially high concentrations in the feline eye (in other words, this reaction is theoretically possible with any fluoroquinolones but enrofloxacin is especially predisposed to causing this reaction).

Enrofloxacin can occasionally lead to the production of enrofloxacin crystals in the urine. For more information, click here.

Page last updated: 12/1/09