Besifloxacin for Veterinary Eye Care: Uses, Dosing, and Benefits for Dogs, Cats, and Horses

Stubborn eye infections in pets are getting trickier. Older drops often stumble against resistant staph, and owners fight a losing battle with dosing every two hours. There’s a newer tool that sticks to the eye longer and hits tough Gram-positives hard: besifloxacin. It isn’t magic, it’s off-label in animals, and it still needs culture and good nursing. But when you pick it for the right case, it can save vision and sleep.

TL;DR: When to Use Besifloxacin in Animal Eyes

• Best fit: moderate-to-severe bacterial conjunctivitis, keratitis, or corneal ulcers where Gram-positive cocci (Staph/Strep) are likely or confirmed-especially if older fluoroquinolones failed.
• Spectrum: potent against Staphylococcus (incl. methicillin-resistant isolates), Streptococcus; decent against some Gram-negatives; Pseudomonas coverage is variable.
• Formulation edge: viscous DuraSite suspension increases corneal contact time, so fewer daily doses than older options.
• Dosing (typical off-label): start q2-4h for ulcers/keratitis in dogs and cats, then taper; q8-12h for simple conjunctivitis; horses often need q4-6h. Shake well.
• Safety: generally well tolerated topically. Avoid delaying antifungals in horses. Use culture/susceptibility when possible. Document off-label use.

I’ll walk through when I choose besifloxacin, how I dose it across species, what to watch for, and how it stacks up against moxifloxacin, ofloxacin, tobramycin, chloramphenicol, and ciprofloxacin.

What It Is and When It Beats Other Drops

Besifloxacin is a fluoroquinolone eye drop (0.6% suspension) developed purely for topical ophthalmic use in humans. That matters: because it isn’t used systemically, there’s less background resistance pressure compared with older, multi-use fluoroquinolones. Its DuraSite vehicle is a gel-like polymer that holds the drug on the ocular surface longer than regular solutions, which boosts exposure between blinks.

Why vets reach for it:

• Resistant Staph and Strep: Low MICs against Staphylococcus aureus and S. pseudintermedius, including many methicillin-resistant isolates. In clinic, that translates to fewer failures when chloramphenicol, fusidic acid, or older quinolones underperform.
• Sticky formulation: The viscous suspension means fewer daily doses for conjunctivitis and better overnight coverage for ulcers compared with plain solutions.
• Mixed infections: Paired with an anti-pseudomonal agent (e.g., tobramycin or compounded amikacin), it gives broad coverage while you wait for culture.

When I’m cautious:

• Melting ulcers with suspected Pseudomonas (especially in dogs): I don’t rely on besifloxacin alone. I add tobramycin or amikacin and start aggressive anti-collagenase therapy immediately.
• Horses in fungal season: Horses love to turn corneal trauma into fungal keratitis. Besifloxacin won’t touch fungi. If the cornea looks gritty, plaque-like, or has feathery edges, I begin antifungals early and don’t let an antibacterial delay that.
• Simple viral conjunctivitis in cats: If feline herpesvirus is driving the show, lubricants and antivirals matter more. I use antibiotics only if there’s bacterial overgrowth or corneal epithelial compromise.

How strong is its coverage? Human ophthalmology studies show potent activity against Gram-positive pathogens common in ocular disease, and practical experience in veterinary patients matches that-especially for staphylococcal blepharoconjunctivitis and infected superficial ulcers. Pseudomonas aeruginosa is hit-or-miss, so I treat it as a bonus, not a guarantee.

Key sources I trust for this: the Besivance (besifloxacin 0.6%) FDA prescribing information (microbiology and dosing studies), Slatter’s Fundamentals of Veterinary Ophthalmology (Hendrix & Maggs, on off-label ophthalmic antibiotics in animals), and ACVO diplomate teaching notes. Culture and susceptibility, guided by CLSI methods, remain the gold standard when the case is severe or not responding.

How to Dose and Use It (Dogs, Cats, Horses)

General rules of thumb before the drop hits the eye:

• Shake the bottle like you mean it. It’s a suspension. Incomplete mixing means unpredictable dosing.
• Clean the discharge first. A gentle sterile saline rinse reduces biofilm and lets drug touch tissue.
• If you’re using multiple drops, wait 5 minutes between them. Ointments go last.
• Do not touch the cornea with the tip. One touch can seed bacteria and trigger a corneal abrasion.

Typical off-label dosing I use or discuss with owners (always refine to the specific case, stain results, pain level, and culture if available):

• Dogs - bacterial conjunctivitis: 1 drop every 8-12 hours for 7-10 days. Recheck if no change in 72 hours.
• Dogs - infected superficial corneal ulcer or keratitis: start 1 drop every 2-4 hours while awake for 24-48 hours, then taper to every 6-8 hours as the epithelium starts to heal. If melting, pair with anti-pseudomonal coverage and anti-collagenase (e.g., autologous serum, EDTA).
• Cats - bacterial conjunctivitis/keratitis: 1 drop every 8-12 hours. If herpes suspected, add antivirals as indicated; avoid steroid drops unless guided by a veterinary ophthalmologist.
• Horses - bacterial keratitis/corneal ulcer: 1-2 drops every 4-6 hours, as part of a broader plan. For equine corneal disease, I involve an ophthalmologist early-progress can be very fast in the wrong direction.

How long? Treat until the cornea is re-epithelialized plus 48-72 hours. The conjunctiva should be quiet, and there should be no stromal haze progression. If you’ve been at it for 3-5 days with no improvement-especially if pain is the same or worse-get cytology and culture if you haven’t already, and rethink the plan.

Special situations:

• Melting ulcers: Intensive therapy (q1-2h while awake) may be lifesaving for the eye. Combine besifloxacin with an agent that reliably hits Pseudomonas (tobramycin/amikacin), plus anti-collagenase and pain control. Recheck daily; consider a conjunctival graft if the cornea thins.
• Post-keratotomy/keratectomy or grid keratotomy: Use under specialist guidance. Choose antibiotics based on the reason for surgery and intraoperative findings.
• Contact lens-related disease in dogs (rare): If present, consider anti-pseudomonal priority agents and stop lens wear.

Owner coaching that matters more than you think:

• One good drop is enough. Flooding the eye only wastes medication and increases runoff onto skin.
• Make it easy: hold the muzzle slightly up, pull the lower lid down to make a “pocket,” drop from above, blink, reward.
• Space the day: breakfast-midday-dinner dosing keeps compliance high. Use phone alarms.
• Storage: room temperature; keep the cap on; discard by the date your vet gives (usually 28 days after opening).

Safety, Resistance, and How It Compares

Safety profile (topical use in animals):

• Local effects: brief stinging, mild redness, or transient blur from the viscous vehicle. Rarely, a sticky residue forms at the canthus-wipe it away with saline.
• Allergy: uncommon but possible. If swelling or intense redness appears right after dosing, stop and call your vet.
• Systemic absorption: minimal, so the cartilage concerns seen with systemic fluoroquinolones in growing animals aren’t a practical issue with topical eye use. Still, don’t overuse antibiotics without cause.
• Breeding, pregnant, lactating animals: safety data in veterinary species are limited; weigh risks and benefits and consider culture-driven alternatives.

Resistance and stewardship:

• Culture early in bad cases. Cytology today, culture tomorrow beats guessing for a week.
• Expect staph shifts. Staphylococcus pseudintermedius is the usual dog culprit. If that’s in play, besifloxacin is a strong first-line choice when the case looks severe or previously treated.
• Don’t use it “just in case” for mild viral disease. Save your big guns for bacterial disease.
• Follow dosing. Underdosing breeds resistance and treatment failure.

How besifloxacin stacks up against other common eye antibiotics we use in dogs, cats, and horses:

Quick pick heuristics I use in practice:

• Likely Staph/Strep (red eye, sticky discharge, blepharitis, dog): choose besifloxacin or moxifloxacin; add lubrication.
• Melting ulcer (green slime, crater, pain): tobramycin or amikacin hourly + besifloxacin + anti-collagenase + atropine for pain. Recheck fast.
• Budget constraints, mild case: ofloxacin or chloramphenicol can be fine if no corneal involvement.
• Horse with stromal haze and plaque: start antibacterial plus antifungal early; do not wait for culture to add antifungal.

Legal and local notes (New Zealand context): In NZ, besifloxacin is a human prescription product. Vets can prescribe it extra-label under professional responsibility when it’s the best option. Get informed owner consent. Chloramphenicol is widely available here and still useful for simple conjunctivitis, but it won’t solve an infected ulcer. Pricing varies; warn owners it’s pricier than older drops.

Checklists, FAQs, and Next Steps

Quick checklist: starting besifloxacin in a pet

• Fluorescein stain first: is the cornea intact? Any melting?
• Cytology if discharge is thick or green: look for cocci vs rods, neutrophils, fungi.
• Culture severe, deep, or non-responding cases before you’ve flooded the eye with multiple drugs.
• Pick frequency based on severity (conjunctivitis q8-12h; ulcers q2-4h initially).
• Add a second drug if rods or melting are suspected (tobramycin/amikacin).
• Analgesia: atropine for ciliary spasm; oral pain relief as needed.
• Owner coaching: shaking, spacing drops, no touching the tip, alarm reminders.
• Recheck timing: 48-72 hours for ulcers; 5-7 days for conjunctivitis.

Mini-FAQ

• Will besifloxacin fix Pseudomonas? It may help, but I don’t count on it. Pair with a proven anti-pseudomonal agent in ulcers.
• Can I use it with serum or EDTA in melting ulcers? Yes. Space applications by 5 minutes to avoid washing out the drop.
• Is it safe for young puppies/kittens? Topical use has minimal systemic absorption. I still use it only when clearly indicated and often for shorter courses.
• My cat has herpes flares. Should I use besifloxacin each time? Only if you see bacterial overgrowth or corneal involvement. Lubrication and antivirals remain the main tools.
• Do I stop as soon as the eye looks better? No. Continue 48-72 hours beyond resolution and follow your vet’s taper plan.
• What if drops are impossible at home? Ask about ointment add-ons, a dosing aid collar, or short inpatient care to stabilize the eye.

Next steps for different scenarios

• Dog with first-time conjunctivitis: stain negative, mild discharge. Start besifloxacin q12h or a budget option; recheck in 5-7 days. If worse, culture.
• Dog with a superficial ulcer after trauma: stain positive, no melting. Besifloxacin q4h for 48 hours, then q8h; add lubrication and atropine. Recheck in 48 hours.
• Dog with melting ulcer: emergency plan with tobramycin/amikacin hourly + besifloxacin q2-4h + serum/EDTA. Analgesia and close monitoring. Consider referral.
• Cat with conjunctivitis and sneezing: suspect herpes. Lubricate, consider antiviral, besifloxacin only if mucopurulent discharge or corneal defect. Keep stress low.
• Horse with corneal haze after a scratch: start broad antibacterial including besifloxacin q6h, plus early antifungal. Daily rechecks. Consider a subpalpebral lavage system for dosing.

When to escalate or switch:

• No improvement after 72 hours in an ulcer, or pain persists: culture, cytology, and consider adding/altering coverage.
• Worsening stromal loss or hypopyon: emergency referral; surgical options may be needed.
• Repeated relapses with staph blepharitis: check eyelids for meibomian disease, treat eyelid hygiene, rule out allergic triggers.

Evidence and credibility notes (for your records and owner discussions): The FDA-prescribing information for besifloxacin (Besivance 0.6%) documents robust Gram-positive activity and the DuraSite contact-time advantage. Human clinical trials show low MICs against MRSA/MRSE; veterinary ophthalmology textbooks (e.g., Slatter’s, Hendrix & Maggs) describe off-label adoption for dogs and cats, with strong anecdotal and case-series support. CLSI susceptibility methods inform culture-based choices, but veterinary-specific ocular breakpoints are limited-interpret MICs with clinical context. University ophthalmology services (e.g., UC Davis VMTH) teach combined regimens for melting ulcers and early antifungal use in horses, which aligns with the approach above.

Final practical tip: besifloxacin earns its keep in the nasty, sticky, resistant cases-and it saves owner sanity thanks to fewer daily doses. Use it deliberately, pair it smartly when rods are in play, and keep rechecks tight.