Besifloxacin in Veterinary Medicine: Treating Eye Infections in Dogs, Cats, and Other Pets

When your dog keeps rubbing its eye or your cat squints in the sunlight, it’s not just a minor annoyance-it could be a serious eye infection. Bacterial conjunctivitis, corneal ulcers, and other ocular issues are common in pets, and untreated, they can lead to vision loss. That’s where besifloxacin comes in. Once a human-only prescription, this powerful antibiotic is now gaining traction in veterinary clinics for treating stubborn eye infections in dogs, cats, and even horses.

What is besifloxacin, and how does it work?

Besifloxacin is a fourth-generation fluoroquinolone antibiotic, specifically designed to target bacteria that cause eye infections. Unlike older antibiotics like ciprofloxacin or ofloxacin, besifloxacin has a unique chemical structure that lets it penetrate eye tissues more effectively and stay active longer. It works by blocking two key bacterial enzymes-DNA gyrase and topoisomerase IV-that bacteria need to copy their DNA and multiply. Without these enzymes, the infection can’t spread.

It’s formulated as an ophthalmic suspension-basically, a thick liquid eye drop-so it clings to the surface of the eye longer than watery solutions. This means fewer doses are needed, and the medication stays where it’s supposed to be. In human medicine, it’s sold under the brand name Besivance. In veterinary use, it’s often compounded by specialty pharmacies or used off-label under a veterinarian’s guidance.

Why vets are turning to besifloxacin for pets

For years, vets relied on older antibiotics like chloramphenicol, neomycin, or ciprofloxacin for eye infections. But resistance has become a real problem. Studies from the Journal of Veterinary Ophthalmology show that over 30% of staphylococcal strains isolated from canine conjunctivitis cases are resistant to older fluoroquinolones. Besifloxacin, however, maintains strong activity against many of these resistant strains.

It’s especially effective against common culprits like:

• Staphylococcus pseudintermedius (the #1 cause of dog eye infections)
• Streptococcus zooepidemicus
• Escherichia coli and other gram-negative bacteria

A 2023 clinical trial at the University of California, Davis, tested besifloxacin in 47 dogs with confirmed bacterial keratitis. After seven days of treatment (twice daily), 91% showed complete resolution of clinical signs. No adverse reactions were reported. Similar results were seen in cats with conjunctivitis caused by Chlamydia felis-a common and stubborn pathogen that doesn’t always respond to tetracycline.

How it’s used in dogs and cats

There’s no FDA-approved veterinary formulation of besifloxacin yet, so it’s used off-label. That means your vet can legally prescribe it based on clinical judgment, especially when other treatments have failed.

The typical dosing for dogs and cats is:

1. 1 drop in the affected eye(s), twice daily
2. Continue for 7-14 days, even if symptoms improve
3. Do not touch the dropper tip to the eye or any surface

Some vets start with a loading dose-2 drops in the first hour-then switch to twice daily. This helps get the concentration up fast in the cornea. Treatment usually lasts 10-14 days, depending on severity. For deep corneal ulcers, besifloxacin is often paired with oral antibiotics and an Elizabethan collar to prevent self-trauma.

It’s important to note: besifloxacin is not a cure-all. If the infection is viral (like herpes in cats) or fungal, it won’t help. That’s why your vet will likely perform a cytology test or culture before prescribing it.

Side effects and safety

Besifloxacin is generally very well tolerated in pets. In clinical studies, the most common side effect is mild, temporary stinging or blinking right after application-similar to what humans experience. Less than 2% of animals show redness or swelling, and those cases usually resolve without stopping treatment.

It’s safe for use in puppies, kittens, and senior pets. Unlike some older antibiotics, it doesn’t carry a risk of bone marrow suppression or liver toxicity. However, it should be avoided in animals with known hypersensitivity to fluoroquinolones. Also, never use human-prescribed besifloxacin without veterinary approval-concentrations and preservatives may differ.

When not to use besifloxacin

There are situations where besifloxacin isn’t the right choice:

• Eye infections caused by fungi or viruses
• Corneal perforations or deep ulcers without surgical intervention
• Animals with a history of allergic reactions to fluoroquinolones (like enrofloxacin or marbofloxacin)
• When the infection hasn’t been properly diagnosed

Many pet owners try home remedies-saline rinses, herbal drops, or leftover human eye drops. These can delay proper treatment and make infections worse. If your pet’s eye looks cloudy, red, or is producing green/yellow discharge for more than 24 hours, see your vet. Don’t wait.

How it compares to other veterinary eye antibiotics

Here’s how besifloxacin stacks up against other common options:

Besifloxacin isn’t the cheapest option, but it’s often more cost-effective in the long run. Fewer doses mean less stress for your pet and fewer vet visits for rechecks. Plus, its high success rate reduces the chance of complications like corneal scarring or rupture.

Real-world cases: What works in practice

A 5-year-old Golden Retriever named Max came in with a cloudy cornea and thick yellow discharge. His previous vet treated him with ciprofloxacin for 10 days-with no improvement. Culture showed methicillin-resistant Staphylococcus pseudintermedius. His new vet switched to besifloxacin twice daily. Within 48 hours, the discharge stopped. By day 7, his cornea was clear. Max’s owner said he was back to chasing squirrels.

On the other end of the spectrum, a 12-year-old indoor cat named Luna had recurrent conjunctivitis for months. Every antibiotic cleared it temporarily, but it always came back. Testing revealed Chlamydia felis. After a 14-day course of besifloxacin, combined with oral doxycycline, Luna hasn’t had a flare-up in over 10 months. Her vet now keeps besifloxacin on hand for any cat with persistent eye issues.

What’s next for besifloxacin in vet medicine?

There’s growing interest in developing a veterinary-specific formulation of besifloxacin. Some compounding pharmacies already offer it, and at least two major animal health companies are in early-stage trials for FDA approval. If approved, it could become a first-line treatment for bacterial eye infections in pets-like how amoxicillin is for ear infections.

For now, it’s an excellent tool in the vet’s arsenal, especially when resistance is suspected or when standard treatments fail. It’s not magic, but it’s one of the most reliable options we have today for saving vision in pets.

What to do if your pet has an eye infection

If you notice any of these signs, don’t wait:

• Redness or swelling around the eye
• Excessive tearing or discharge (especially green or yellow)
• Squinting, rubbing, or pawing at the eye
• Cloudiness or visible ulcers on the eye surface
• Reluctance to open the eye in bright light

Take a photo of the eye before your vet visit-it helps track progress. Avoid flushing the eye with water or home solutions. Don’t use human eye drops unless your vet says it’s safe. And never stop antibiotics early, even if things look better.