Marbofloxacin
**Marbofloxacin** is a synthetic, broad-spectrum **fluoroquinolone antibiotic** used primarily in veterinary medicine. It exhibits **concentration-dependent bactericidal activity** and a significant **post-antibiotic effect (PAE)** for both gram-negative and gram-positive bacteria. It is active in both stationary and growth phases of bacterial replication. * **Spectrum of Activity**: Highly effective against a wide range of gram-negative bacilli and cocci (e.g., *Pseudomonas aeruginosa*, *E. coli*, *Klebsiella*, *Enterobacter*, *Proteus*, *Salmonella*) and some gram-positive organisms (e.g., *Staphylococcus* spp., including penicillinase-producing strains). * **Clinical Pearl**: Like other fluoroquinolones, marbofloxacin has weak activity against most anaerobes and variable/poor efficacy against *Streptococcus* species. It is not recommended for anaerobic or streptococcal infections. * **Resistance**: Occurs primarily via chromosomal mutation (especially in *Pseudomonas*, *Klebsiella*, and *Enterococci*); plasmid-mediated resistance is rare.
Mechanism: Marbofloxacin exerts its bactericidal effect by targeting key bacterial enzymes involved in DNA replication and transcription: * Inhibits **DNA-gyrase** (topoisomerase II) โ prevents DNA supercoiling. * Inhibits **Topoisomerase IV** โ prevents separation of interlinked daughter DNA molecules. * **Result**: Disruption of DNA replication, transcription, and repair โ rapid bacterial cell death (typically within 20-30 minutes of exposure).
Dosing by species
- For susceptible infections (urinary tract, skin and soft tissue) ยท 2.75-5.5 mg/kg PO once daily ยท PO ยท q24h ยท Give for 2-3 days beyond cessation of clinical signs (skin/soft tissue); at least 10 days (urinary tract). Max 30 days. ยท If no improvement noted after 5 days, reevaluate diagnosis.
- First-line treatment for feline tuberculosis or non-tuberculous mycobacteria (NTM) ยท 2 mg/kg PO once daily ยท PO ยท q24h ยท Pending definitive diagnosis. Not effective against MAC infection.
- For hemoplasmosis ยท 2.75 mg/kg PO once daily (q24h) ยท PO ยท q24h
- Susceptible bacterial infections ยท 2 mg/kg ยท IV/SC/PO ยท q24h ยท Not specified ยท Do not use 20 mg or 80 mg tablets. May allow clearance of Mycoplasma haemofelis in persistently infected cats.
- Susceptible infections ยท 10 mg/kg PO at least every 48 hours ยท PO ยท q48h ยท Study done in Ball pythons (Python regius). Further studies required to determine effective doses and toxicity.
- For susceptible infections (urinary tract, skin and soft tissue) ยท 2.75-5.5 mg/kg PO once daily ยท PO ยท q24h ยท Give for 2-3 days beyond cessation of clinical signs (skin/soft tissue); at least 10 days (urinary tract). Max 30 days. ยท If no improvement noted after 5 days, reevaluate diagnosis.
- For susceptible Pseudomonas otitis ยท 5.5 mg/kg PO once daily ยท PO ยท q24h ยท Dose at the high end of the flexible dosing label for severe/chronic cases or when topical therapy is not possible.
Routes of administration
Contraindications
- Hypersensitivity to fluoroquinolones
- Small and medium breed dogs up to 8 months of age
- Large breed dogs up to 12 months of age
- Giant breed dogs up to 18 months of age
- Cats under 12 months of age
- Food-producing animals (FDA prohibited)
- Cats (do not use 20 mg and 80 mg tablets)
- Dogs < 12 months of age
- Giant-breed dogs < 18 months of age
- Cats < 16 weeks of age
Adverse effects
- Gastrointestinal distress (vomiting, anorexia, soft stools, diarrhea)
- Decreased activity/lethargy
- Cartilage abnormalities in young, growing animals
- Elevated hepatic enzymes (rare)
- Ataxia, seizures, depression, nervousness (rare)
- Hypersensitivity reactions (rare)
- Crystalluria (rare)
- Potential ocular toxicity/blindness in cats (rare/unproven, but reported)
- Gastrointestinal signs (nausea, vomiting)
- Potential CNS toxicity (seizures)
- Cartilage abnormalities in growing animals
- Potential retinal toxicity/blindness in cats (at high doses)
Drug interactions
- Antacids / Dairy Products ยท Cations (Mg++, Al+++, Ca++) may bind to marbofloxacin and prevent its absorption; separate doses by at least 2 hours
- 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 systemically used cyclosporine
- Flunixin ยท May increase AUC and elimination half-life of the fluoroquinolone, and vice versa (extrapolated from enrofloxacin)
- Glyburide ยท Severe hypoglycemia possible
- Iron, Zinc (oral) ยท Decreased marbofloxacin absorption; separate doses by at least two hours
- Methotrexate ยท Increased MTX levels possible with resultant toxicity
- Nitrofurantoin ยท May antagonize the antimicrobial activity of fluoroquinolones; concomitant use not recommended
- Phenytoin ยท Marbofloxacin may alter phenytoin levels
- Probenecid ยท Blocks tubular secretion and may increase blood level and half-life of marbofloxacin
- Quinidine ยท Increased risk for cardiotoxicity
- Sucralfate ยท May inhibit absorption of marbofloxacin; separate doses by at least 2 hours ยท major
Monitoring
- Clinical efficacy (resolution of infection)
- Adverse effects (GI distress, CNS signs)
- Joint health/lameness in younger animals (if inadvertently used)
- Clinical efficacy and resolution of infection
- Culture and susceptibility results
- Signs of gastrointestinal upset
- Neurological signs (especially in patients with a history of seizures)
- Vision changes or mydriasis in cats
Overdose
Acute overdoses of marbofloxacin are unlikely to result in signs more serious than **anorexia or vomiting**, though other adverse effects (like CNS stimulation) could theoretically occur. * **Chronic Toxicity**: In safety studies, dogs receiving massive overdoses (55 mg/kg per day for 12 days) developed anorexia, vomiting, dehydration, tremors, red skin, facial swelling, lethargy, and weight loss. * **Treatment**: Management of overdose consists of drug withdrawal and symptomatic/supportive care. If ingestion was recent, gastrointestinal decontamination (emesis or activated charcoal) may be considered.
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.