Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066




(for veterinary information only)



100 mg, 250 mg, 500 mg, 750 mg & 1000 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 ciprofloxacin which was produced for human use and enrofloxacin for animal use). 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 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.

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. Ciprofloxacin is approved for human use and is converted to enrofloxacin within the body. Because of inexpensive generics are available for ciprofloxacin, it is tempting to use ciprofloxacin in pets instead of enrofloxacin. There are two reasons why this is not the greatest idea. The first is that antibiotic use creates bacterial resistance and ciprofloxacin is a key treatment in many human diseases. If resistance to ciprofloxacin develops, human life could be lost. This is a basic tenet of responsible antibiotic use which can be extended to the use of any antibiotic.

DNA Double Helix
DNA Double Helix
(Photocredit: NIH Public Image Library)

The second issue with ciprofloxacin use in pets is that bioavailability is highly variable between individuals. This means that a particular dose of ciprofloxacin might be absorbed just fine by one dog and not at all by another, yielding an unpredictable response or lack thereof. Higher doses are recommended to get the most medication into the patient's body where it can achieve its effect.


This medication may be used in either dogs or cats to combat different types of infections, especially those involving Pseudomonas; however, it may be best to consider a different quinolone class antibiotic. While ciprofloxacin can be used in cats, bioavailability is low (most of the drug does not enter the cat's body effectively) and bioavailability is somewhat unpredictable in the dog which means higher doses must be used. More consistent results are expected in quinolones approved for veterinary use. (Ciprofloxacin is approved for human use but inexpensive generics are available which has led to a great deal of veterinary use).

Ciprofloxacin is 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.

Ciprofloxacin 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.

If you skip a dose, do not double up on the next dose.

Store at room temperature, protected from light.


As with most oral medications, the most common side effects of ciprofloxacin are related to the GI tract: vomiting, diarrhea, reduced appetite.

In immature dogs (less than 8 months of age) damage to developing 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.

Quinolone class antibiotics are taken up by the feline retina and this accumulation can cause blindness. Since ciprofloxacin is not very bioavailable in the cat, higher doses are needed to achieve an antibiotic effect. These doses could lead to blindness in the cat.

Fluoroquinolone antibiotics may lower the seizure threshold and increase a patient's tendency to have seizures. This is of no concern in a normal animal but is worth a cautionary statement for patients with a pre-existing seizure disorder.

Ciprofloxacin has been known to form crystals in urine and form actual bladder stones in human beings. Hydration should be maintained in pets taking ciprofloxacin to avoid any issues.


Sucralfate (a medication used to treat stomach ulcers) may bind ciproflxacin and prevent it from entering the body. These medications should be given at least 2 hours apart if they are used together. A similar phenomenon occurs with magnesium and calcium-containing antacids.

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

If ciprofloxacin 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 ciprofloxacin and prevent absorption into the body. Such medications should be separated from ciprofloxacin by at least 2 hours.

Concurrent use of ciprofloxacin and sildenofil can increase sildenofil levels into a toxic range.


Pseudomonas infections are especially common in canine ears and if not controlled decisively, can become resistant. Higher doses of fluoroquinolones are needed to kill this particularly nefarious bacterium and there is significant expense associated. It is tempting to use ciprofloxacin as there is an inexpensive generic but if bioavailability proves inadequate and the infection prevails, it will become even more difficult to clear. In other words, it may not be worth taking a chance on using an inexpensive medication and the use of ciprofloxacin in this situation should be carefully weighed against the monetary savings.

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


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

Page posted: 3/19/2016
Page last updated: 2/3/2022