Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066




(for veterinary information only)




22.7 mg, 68 mg, and 136 mg



Human beings have been at odds with microbes since the beginning of time and the quest for new medications continues even today. When sulfa drugs came on the scene in the 1940's, an "age of antibiotics" was born and a new dimension had opened in the combat against microbes. From there a proliferation of antibiotics developed, each new medication exploiting a different aspect of bacterial metabolism until it seemed that the war on microbes would soon be won.

Despite this progress, one particular bacterial species remained seemingly invincible: Pseudomonas aeruginosa. This species of bacteria was able to change its antibiotic susceptibility with each antibiotic exposure, become resistant to multiple drugs in response to every medication used against it. Eventually, the aminoglycoside class of antibiotics was developed and there was finally a way to kill Pseudomonas fairly reliably but the price was that medication was injectable only, necessitating hospitalization for the patient, and potential kidney damage could result with prolonged use.

A major breakthrough against Pseudomonas came with 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. Enrofloxacin is the veterinary fluoroquinolone introduced by Bayer to address the need for treatment of Pseudomonas infections in pets. It was the first quinolone for veterinary use and despite decades of use, still dominates the quinolone class for animal use.

Helix Model Small
DNA strand
(Photocredit: NIH Public Image Library)


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 of DNA to be used in protein production must be uncoiled by an enzyme called DNA gyrase. The fluoroquinolone antibiotics deactivate DNA gyrase making the reading of DNA impossible. The bacterial cell dies. Mammalian DNA gyrase is of a completely different shape and remains untouched.


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. It is not helpful against anaerobic infections, however, 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 chewables or enteric coated. The coated tablets should not be crushed as they taste very bitter and releasing this flavor is likely to lead to rejection of the medication.



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 know about those as well. Nausea is most commonly a problem when higher doses of enrofloxacin are used, as in a known Pseudomonas infection

Common side effects for enrofloxacin are upset stomach, as is can be seen with any oral medication. In most cases this would be vomiting or appetite loss and giving the medication with food should solve the problem. The use of enrofloxacin can produce crystals in 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 side effect. Enrofloxacin crystals should not be confused with more clinically relevant struvite, oxalate, or urate crystals.

Severe side effects:

  • In immature dogs (less than 8 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 medication in puppies unless the severity of the infection present warrants it.
  • In infections with Strep. canis a drug interaction can occur between enrofloxacin and the bacteria that leads to "necrotizing fasciitis" 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 in the cat (dilated pupils and blindness) can occur in higher doses (see below).


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 into the body. Such medications should be separated from enrofloxacin by at least 2 hours. For this reason, cheese is not a good treat in which to hide enrofloxacin pills.

Enrofloxacin synergizes with numerous other antibiotics which means that the effects of the two antibiotics together is greater than one would expect. This phenomenon adds a boost to treatment of infections of many types.



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; fortunately, generic tablets have become available to mitigate the 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.

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

Retinal damage has been seen in cats especially when higher doses (such as might be used to treat a Pseudomonas ear infection) are used. This reaction is not common but has been seen even with fairly routine dosages. There is no way to predict which cats will react. As a result, feline dosing schedules involve relatively low doses of enrofloxacin and another quinolone is best selected if the infection is expected to be resistant. Blindness, temporary or permanent, can result. Kidney disease predisposes a cat to retinal damage from enrofloxacin.

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

black and white catNote the concerns about retinal damage
and watch your cat for dilated pupils,
bumping into things, misjudging jumping
distances or other signs of vision loss.


 Enrofloxacin should not be given with calcium-rich foods such as cheese as calcium may interfere with absorption.


Short version (to help us comply with "Lizzie's Law")

Page last updated: 10/16/2021