Baytril for Dogs and Cats: Dose Chart and How Long It Lasts

Baytril is the brand name for enrofloxacin, a prescription antibiotic from the fluoroquinolone family. Vets use it for bacterial infections in dogs and cats, including skin wounds and abscesses, and in dogs also airway, lung and bladder infections. A dose leaves the body fairly quickly: in a healthy dog, most of it is gone within about 8 to 15 hours. In cats it lingers longer, and cats also have a strict upper dose limit because higher doses can damage the retina.

Every number in the dose chart below comes from the FDA-approved label, with a link to it, and the calculator turns that range into milligrams for your pet's weight. Neither replaces the prescription: your veterinarian sets the dose.

What Is Baytril Used For?

Baytril tablets (sold as Baytril Taste Tabs) are FDA-approved for dogs and cats with infections caused by bacteria that enrofloxacin can kill. In the label's field studies, the drug worked for:

• Dogs: skin infections (wounds and abscesses), respiratory infections (pneumonia, tonsillitis, rhinitis) and bladder infections (cystitis).
• Cats: skin infections (wounds and abscesses).

For more on bacterial skin infections, see our guide to pyoderma in dogs. For outer ear infections, there is a separate product, Baytril Otic, an ear emulsion for dogs that pairs enrofloxacin with silver sulfadiazine. The silver sulfadiazine is what handles yeast and fungi; enrofloxacin on its own only works on bacteria.

Baytril comes in three forms in the US:

• Taste Tabs (22.7, 68 and 136 mg tablets) for dogs and cats.
• Injectable Solution 2.27% for dogs only, given by the vet as a first dose.
• Baytril Otic ear drops for dogs only.

Elanco sells Baytril today. The Baytril name still belongs to Bayer and is used under license, which is why older articles call it a Bayer product. A separate Baytril 100 injection is approved for cattle and pigs; it is not a pet product.

How Does Baytril Work?

Enrofloxacin is a broad-spectrum antibiotic that blocks two bacterial enzymes, DNA gyrase and topoisomerase IV. Bacteria need them to copy their DNA, so the bacteria die rather than just stop growing. In vet terms, the drug is bactericidal.

It works on both Gram-negative and Gram-positive bacteria. Organisms it is usually active against include:

• E. coli
• Salmonella
• Pseudomonas aeruginosa
• Staphylococcus species
• Mycoplasma

It does not reliably cover anaerobic bacteria (the kind that thrive without oxygen, common in deep wounds and dental disease) or most enterococci. Resistance is also rising, so the Merck Veterinary Manual recommends basing fluoroquinolone use on a culture and susceptibility test whenever possible. That test grows the bacteria from your pet's sample and checks which antibiotics still kill them.

Enrofloxacin is what pharmacologists call concentration-dependent: how well it kills depends on how high the drug level gets compared with the amount needed to stop that particular bacterium. That is why it is usually given once a day at a full dose rather than in many small doses. In dogs, about 80% of an oral dose reaches the bloodstream, and blood levels peak about an hour after a tablet. The drug reaches most tissues and gets especially concentrated in urine.

How Long Does Baytril Stay in a Dog's System?

The short answer: most of a dose is cleared within about 8 to 15 hours in a healthy dog.

Here's where that number comes from. The Baytril label gives the elimination half-life, the time it takes for the drug level in the blood to drop by half. In dogs it is about 2.5 to 3 hours. The Merck Veterinary Manual explains that most of a drug is eliminated after 3 to 5 half-lives. Multiply the two and you get roughly 8 to 15 hours.

Treat these as estimates, not a timer:

• The label measured them at a low test dose in healthy animals. The label says how the body handles doses above 11.5 mg/kg twice a day in dogs is unknown, and in cats it only has data for that one test dose.
• Kidney or liver disease slows clearance. The kidneys remove most of the drug, and Merck notes that kidney failure impairs clearance enough that dose changes are needed.
• The body converts part of each dose into ciprofloxacin, another active antibiotic, so the antibacterial effect isn't only the parent drug.
• Levels in the urine stay high for about 24 hours after a dose, which is one reason the drug suits bladder infections.

If the drug is gone in half a day, why does once a day work? Because the killing depends on the peak level, not on keeping the drug in the blood around the clock. At the label's test dose, tissue levels stayed above what common bacteria need for 8 to 12 hours.

You may notice your pet feeling better within a few days. The label tells vets to re-check the diagnosis if there is no improvement within five days, so call your vet if that happens.

Baytril Dosage Chart for Dogs and Cats

All doses below come from the current FDA-approved Elanco labels. The tablet dose is a daily amount, given once a day or split into two equal doses 12 hours apart.

For information only. These are typical published dose ranges, not a prescription and not medically verified for your pet. Your veterinarian sets the dose after examining your pet. Never start, stop or change a medicine without their OK.

Only give what your vet prescribed, at the dose they set.

A few things the chart can't show:

• Cats have a hard ceiling. The label says not to exceed 5 mg/kg of body weight per day in cats because of retinal toxicity. That is the whole daily amount, whether it is given once or split. The Merck Veterinary Manual is more cautious still: it says enrofloxacin "probably should not be used in cats."
• The dog range is wide on purpose. The vet picks a point between 5 and 20 mg/kg based on the infection, how sick the dog is and how sensitive the bacteria are. Dogs on the higher end should be watched for poor appetite, low energy and vomiting.
• Young dogs are a separate question. Small and medium breed puppies between 2 and 8 months old should not get Baytril, and safety isn't established for large breeds up to a year or giant breeds up to 18 months (more below).

Giving Baytril at Home

• Dogs: most take Taste Tabs willingly from your hand. You can also hide the tablet in food or give it like any other pill.
• Cats: the label says to pill cats rather than offer the tablet. Here's how to give a cat a pill without a fight.
• Watch your pet afterward to make sure the whole dose went down.

• Antacids, calcium (including dairy), iron, zinc, magnesium and aluminum products can reduce how much enrofloxacin is absorbed. Ask your vet how to time them if your pet takes any.
• Missed a dose? Ask your vet what to do. Don't double up the next dose on your own; in cats that would break the daily limit.
• Give it for as long as your vet says, even if your pet seems better.
• Wash your hands after handling tablets or ear drops and keep the drug away from your eyes. Anyone with a known allergy to quinolone antibiotics should avoid handling it.

Side Effects and Drug Reactions

In the label's field studies, side effects were uncommon. Two of 270 dogs (0.7%) vomited, and both recovered on their own. None of the 124 cats treated at 5 mg/kg for 10 days had drug-related side effects. Reports collected after approval add a longer, rare list.

Dogs (rare):

• Poor appetite, diarrhea, vomiting
• Raised liver enzymes on bloodwork
• Wobbly walking (ataxia) and seizures
• Depression, lethargy, nervousness

Cats (rare):

• Dilated pupils, damage to the retina and vision loss
• Vomiting, poor appetite, diarrhea, raised liver enzymes
• Wobbly walking and seizures
• Depression, lethargy, vocalizing, aggression

Other things your vet may watch for: crystals in very concentrated, acidic urine (their clinical importance is unclear), and changes in liver enzymes or kidney values on bloodwork.

Why Cats Have a Dose Limit

Cats carry a version of a transport protein (ABCG2) that normally keeps fluoroquinolones out of the retina, the light-sensing layer at the back of the eye. In cats, four changes in that protein weaken the barrier, so the drug can build up in the retina and damage it.

In the label's safety study, cats given 20 mg/kg a day or more developed retinal lesions, abnormal retinal tests and, in some, blindness. Cats on 5 mg/kg did not. Risk factors named in a JAVMA review include high doses, rapid IV infusion, long courses and age, and Merck adds that kidney disease may raise the risk.

Merck ties its stricter line to how the drug works: fluoroquinolones kill by peak concentration, and on that basis it concludes enrofloxacin probably should not be used in cats. Your vet weighs that against the infection and may pick a different antibiotic. If your cat is on Baytril, dilated pupils can be the first sign of retinal changes, so check its eyes.

When to Call Your Vet

Call now (or go to an emergency clinic):

• A seizure, collapse or severe wobbliness
• Your cat's pupils look large, or it bumps into things or seems not to see
• Trouble breathing or a swollen face after a dose (a possible allergic reaction)
• Your pet got an extra dose or chewed into the bottle. Call your vet or a 24/7 poison line: ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661. A fee may apply.

See your vet soon (call the same day):

• Vomiting, diarrhea or refusing food that doesn't settle
• Limping, stiff joints or reluctance to walk in a young dog
• With Baytril Otic: your dog seems unable to hear or loses its balance
• No improvement after five days of treatment

Tell Your Vet Before Starting Baytril

Several of Baytril's risks depend on the pet, the dose and other drugs. Your vet can plan around them if they know:

• Every medicine and supplement your pet takes, including vitamins and anything over the counter. Merck lists these interactions:
  • Antacids and other products with calcium, iron, zinc, magnesium or aluminum, and sucralfate (an ulcer drug), which reduce absorption
  • Theophylline (an airway drug), and caffeine or theobromine, which can build up to toxic levels
  • Nitrofurantoin, which can weaken Baytril against urinary infections
  • Cyclosporine, whose levels rise with fluoroquinolones in people
• Any seizure history or other brain or nerve problem.
• Kidney or liver disease. The kidneys clear most of the drug.
• Age and expected adult size for a young dog, since the cartilage rule depends on breed size.
• Pregnancy, nursing or breeding plans. A dog reproduction study at 15 mg/kg a day found no effects, but safety in breeding or pregnant cats has not been established. Merck notes that large doses during pregnancy may cause embryo loss.
• Any past reaction to a quinolone antibiotic.

When Not to Give Baytril to Dogs and Cats

The label separates hard "no" cases from situations that need caution.

Do not give (label contraindications):

• Dogs or cats allergic to quinolone antibiotics.
• Small and medium breed puppies between 2 and 8 months old. In studies, growing puppies developed cartilage lesions and an abnormal stance in the wrist joints.

Safety not established:

• Large breed dogs up to about 1 year old and giant breeds up to about 18 months, while they are still growing fast.
• Breeding or pregnant cats.

Use with caution, your vet decides:

• Baytril Otic before the vet has checked that the eardrum is intact. The label asks for that check first.
• Pets with seizures or other central nervous system disorders. Quinolones have, rarely, triggered seizures in these animals.
• Pets with kidney disease, including cats with kidney disease, because the drug clears more slowly.
• Cats in general, because of the retina risk.

Like any antibiotic, Baytril does nothing against viruses. Using it when it isn't needed, or against bacteria that are already resistant, helps resistance spread. That's why your vet may want a culture before choosing it, especially for repeat infections.

Originally written by Dr. Catharina Hjorth. Updated by the I Love Veterinary editorial team.

Sources

• Elanco via DailyMed: Baytril (enrofloxacin) Taste Tabs label, NADA 140-441
• Elanco via DailyMed: Baytril Injectable Solution 2.27% For Dogs Only, NADA 140-913
• Elanco via DailyMed: Baytril Otic (enrofloxacin/silver sulfadiazine), NADA 141-176
• Elanco via DailyMed: Baytril 100 injectable for cattle and swine, NADA 141-068
• Merck Veterinary Manual: Quinolones, Including Fluoroquinolones, for Use in Animals
• Merck Veterinary Manual: Pharmacokinetics
• Wiebe V, Hamilton P. Fluoroquinolone-induced retinal degeneration in cats. JAVMA, 2002
• Ramirez CJ et al. Molecular genetic basis for fluoroquinolone-induced retinal degeneration in cats. Pharmacogenetics and Genomics, 2011
• ASPCA Animal Poison Control Center
• Pet Poison Helpline

This article is for general information and is not a substitute for advice from your veterinarian.