Orbifloxacin
Orbifloxacin is a synthetic, broad-spectrum **fluoroquinolone antibiotic** used primarily in veterinary medicine. It exhibits **concentration-dependent bactericidal activity** and possesses a significant **post-antibiotic effect (PAE)**, meaning bacterial growth continues to be suppressed even after drug concentrations fall below the minimum inhibitory concentration (MIC). It is highly effective against aerobic gram-negative bacilli (e.g., *E. coli*, *Klebsiella*, *Proteus*, *Enterobacter*, *Pasteurella*) and some gram-positive cocci (e.g., *Staphylococcus intermedius*, *S. aureus*). > **Clinical Pearl:** Like other fluoroquinolones, orbifloxacin has poor efficacy against obligate anaerobes and most *Enterococcus* species. It should be reserved for infections where culture and susceptibility testing indicate its necessity, promoting responsible antimicrobial stewardship.
Mechanism: Fluoroquinolones exert their bactericidal effect by targeting two essential bacterial enzymes: * **DNA Gyrase (Topoisomerase II):** The primary target in gram-negative bacteria. It prevents the relaxation of positively supercoiled DNA, which is required for normal transcription and replication. * **Topoisomerase IV:** The primary target in gram-positive bacteria. It interferes with the separation of interlinked replicated DNA molecules. **Mechanism Pathway:** Orbifloxacin binds to the enzyme-DNA complex โ inhibits DNA replication and transcription โ induces double-stranded DNA breaks โ rapid bacterial cell death.
Dosing by species
- Susceptible infections ยท 2.5 mg/kg-7.5 mg/kg ยท PO ยท once daily ยท Tablets. Higher end of the dosing range may be necessary for complicated infections.
- Skin infections (wounds and abscesses) ยท 7.5 mg/kg ยท PO ยท once daily ยท Suspension. For susceptible strains of S. aureus, E. coli, and P. multocida.
- Skin and other soft tissue infections ยท 7.5 mg/kg ยท PO ยท q24h ยท Caution with higher doses due to risk of retinal blindness.
- Susceptible infections ยท 5 mg/kg ยท PO ยท once daily
- Susceptible infections ยท 7.5 mg/kg ยท PO ยท once daily
- Susceptible infections ยท 2.5 mg/kg-7.5 mg/kg ยท PO ยท once daily ยท Tablets. Higher end of the dosing range may be necessary in hospitalized patients, those with underlying disease, structural alterations, or infections caused by 'problem' pathogens.
- Urinary tract infections (cystitis) and skin/soft tissue infections (wounds and abscesses) ยท 2.5-7.5 mg/kg ยท PO ยท once daily ยท Suspension.
- Bacterial cystitis ยท 2.5 mg/kg ยท PO ยท q24h
- Skin and other soft tissue infections ยท 7.5 mg/kg ยท PO ยท q24h
Routes of administration
Contraindications
- Immature dogs during the rapid growth phase (2-8 months in small/medium breeds; up to 18 months in large/giant breeds)
- Known hypersensitivity to orbifloxacin or other quinolones
- Giant-breed dogs <18 months old
- Large breeds <12 months old
- Small and medium-sized breeds <8 months old
- Pregnant or lactating bitches
- Animals intended for breeding
- Animals <4 months of age (otic preparation)
- Animals with a ruptured tympanum (otic preparation)
Adverse effects
- Anorexia
- Vomiting
- Diarrhea
- Arthropathies (cartilage damage) in immature, growing animals
- Potential retinal toxicity/blindness in cats (rare, but reported with higher doses of fluoroquinolones)
- CNS stimulation (rare)
- Cartilage abnormalities in growing animals
- CNS adverse effects (potentiated by NSAIDs)
- Retinal blindness in cats (dose-dependent)
Drug interactions
- Antacids / Dairy Products ยท Cations (Mg++, Al+++, Ca++) bind to orbifloxacin and prevent its absorption; separate doses by at least 2 hours.
- Other Antibiotics (Aminoglycosides, 3rd-gen cephalosporins, extended-spectrum penicillins) ยท Unpredictable synergism may occur against some bacteria (particularly Pseudomonas aeruginosa).
- Cyclosporine ยท May exacerbate nephrotoxicity and reduce the metabolism of systemic cyclosporine.
- Flunixin ยท May increase the AUC and elimination half-life of fluoroquinolones.
- Glyburide ยท Severe hypoglycemia is possible.
- Iron, Zinc (oral) ยท Decreased orbifloxacin absorption; separate doses by at least 2 hours.
- Methotrexate ยท Increased methotrexate levels possible, resulting in toxicity.
- Nitrofurantoin ยท May antagonize the antimicrobial activity of fluoroquinolones; concomitant use is not recommended.
- Phenytoin ยท May alter phenytoin levels.
- Probenecid ยท Blocks tubular secretion, potentially increasing blood levels and half-life of orbifloxacin.
- Sucralfate ยท May inhibit absorption of orbifloxacin; separate doses by at least 2 hours. ยท major
- Theophylline ยท May increase theophylline blood levels. ยท major
Monitoring
- Clinical efficacy (resolution of infection)
- Gastrointestinal signs (appetite, vomiting, diarrhea)
- Vision changes or pupillary dilation in cats
- Neurological signs (seizures) in predisposed patients
Overdose
In dogs, receiving up to 5X the maximum dose (37.5 mg/kg) for 30 days did not result in any significant adverse effects. In cats, receiving higher dosages exhibited soft feces and decreased body weight gains.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.