Ciprofloxacin
**Ciprofloxacin** is a second-generation **fluoroquinolone antibiotic** widely used in human medicine and frequently utilized off-label in veterinary medicine. * **Spectrum of Activity**: Broad-spectrum, highly effective against many gram-negative bacilli and cocci (including *Pseudomonas aeruginosa*, *E. coli*, *Klebsiella* spp.) and some gram-positive organisms (like *Staphylococcus* spp., including methicillin-resistant strains). It has weak activity against anaerobes and most *Streptococci*. * **Pharmacokinetic Pearl**: In dogs, its oral bioavailability is significantly lower and more erratic than enrofloxacin (only ~40-50% compared to enrofloxacin's >80%). Therefore, it is generally not considered a direct 1:1 oral substitute for enrofloxacin in canines. * **Clinical Utility**: Often selected when a true intravenous (IV) fluoroquinolone formulation is required, for specific culture-directed therapies, or when a larger oral dosage form is desired.
Mechanism: Ciprofloxacin is a **bactericidal**, **concentration-dependent** antibiotic. * It enters the bacterial cell and inhibits two key type-II topoisomerase enzymes: **DNA gyrase** (primary target in gram-negative bacteria) and **Topoisomerase IV** (primary target in gram-positive bacteria). * Inhibition of these enzymes โ prevents DNA supercoiling and relaxation โ halts DNA replication and transcription โ rapid bacterial cell death (within 20-30 minutes of exposure). * Exhibits a significant **post-antibiotic effect (PAE)**, meaning bacterial growth continues to be suppressed even after drug concentrations fall below the minimum inhibitory concentration (MIC).
Dosing by species
- Susceptible infections ยท 5-15 mg/kg PO q12h ยท PO ยท q12h ยท Avoid or reduce dosage in severe renal failure; avoid in young animals or pregnant/breeding animals.
- Ocular infections ยท 1 drop to affected eye ยท topical ยท q6h ยท Not specified ยท Standard therapy
- Severe ocular infections (intensive therapy) ยท 1 drop to affected eye ยท topical ยท q30-120mins ยท 1-2 days ยท For short-term intensive use
- Susceptible infections ยท 5-15 mg/kg PO twice daily ยท PO ยท twice daily
- Susceptible gram-negative infections ยท 20-40 mg/kg PO twice daily ยท PO ยท twice daily ยท Using ciprofloxacin 500 mg tablets. Crushed tablet goes into suspension well, but must be shaken well before administering.
- Susceptible gram-negative infections ยท 20 mg/kg PO q12h ยท PO ยท q12h ยท Using crushed tablets
- Susceptible gram-negative infections ยท 10-15 mg/kg PO q12h ยท PO ยท q12h ยท Using crushed tablets or suspend
- Susceptible infections (Ratites) ยท 3-6 mg/kg PO twice daily ยท PO ยท twice daily
- Susceptible infections (Rabbits) ยท 5-20 mg/kg PO q12h ยท PO ยท q12h
Routes of administration
Contraindications
- Hypersensitivity to fluoroquinolones
- Small and medium breed dogs 2-8 months of age (due to cartilage damage)
- Large and giant breed dogs during their rapid growth phase (past 8 months of age)
- Known hypersensitivity to ciprofloxacin or other fluoroquinolones
Adverse effects
- GI distress (vomiting, anorexia)
- Cartilage abnormalities in young, growing animals
- CNS stimulation (dizziness, seizures)
- Crystalluria
- Hypersensitivity reactions
- Local irritation after application
- Local burning and itching (reported in humans)
- Lid margin crusting (reported in humans)
- Hyperaemia (reported in humans)
- Taste disturbances (reported in humans)
- Corneal staining (reported in humans)
- Keratitis (reported in humans)
- Lid oedema (reported in humans)
- Lacrimation (reported in humans)
- Photophobia (reported in humans)
- Corneal infiltrates (reported in humans)
Drug interactions
- Antacids/Dairy Products (Mg++, Al+++, Ca++) ยท May bind to ciprofloxacin and prevent its absorption; separate doses by at least 2 hours
- Antibiotics (aminoglycosides, 3rd-generation cephalosporins, extended-spectrum penicillins) ยท Synergism may occur against some bacteria (particularly Pseudomonas aeruginosa)
- Cyclosporine ยท May exacerbate nephrotoxicity and reduce the metabolism of cyclosporine
- Glyburide ยท Severe hypoglycemia possible
- Iron, Zinc (oral) ยท Decreased ciprofloxacin 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 May alter phenytoin levels
- Probenecid ยท Blocks tubular secretion of ciprofloxacin and may increase its blood level and half-life
- Quinidine ยท Increased risk for cardiotoxicity
- Sucralfate ยท May inhibit absorption of ciprofloxacin; separate doses by at least 2 hours
- Theophylline ยท May increase theophylline blood levels
Monitoring
- Clinical efficacy
- Adverse effects (GI signs, CNS stimulation)
- Hydration status
- Clinical resolution of ocular infection
- Corneal healing (via fluorescein staining)
- Signs of local irritation or hypersensitivity
Overdose
Little specific information is available for ciprofloxacin overdosage in veterinary species. Overdoses may result in GI distress, CNS signs (tremors, seizures), or renal toxicity (crystalluria). Treatment should consist of supportive care, maintaining adequate hydration to prevent crystalluria, and gastric decontamination if ingestion was recent. See the enrofloxacin monograph for more extrapolated information.
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.