Norfloxacin — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	5-10 mg/kg	q12h	Duration: 5-14 days depending on infection Notes: Administer on an empty stomach, 1 hour before or 2 hours after meals. Avoid concurrent administration with antacids, sucralfate, or dairy products.
Cat	PO	5-10 mg/kg	q12h	Duration: 5-14 days Notes: Use with caution in young cats due to potential cartilage effects. Administer on an empty stomach.
Horse	PO	5-10 mg/kg	q12h	Duration: 5-10 days Notes: Not commonly used; other fluoroquinolones (e.g., enrofloxacin) are preferred. Administer on an empty stomach.
Cattle	PO	5-10 mg/kg	q12h	Duration: 3-5 days Notes: Extra-label use only; not approved for food animals in many countries. Observe withdrawal times.
Small Ruminants (sheep/goats)	PO	5-10 mg/kg	q12h	Duration: 3-5 days Notes: Extra-label use only; not approved for food animals in many countries. Observe withdrawal times.
Rabbit	PO	5-10 mg/kg	q12h	Duration: 5-10 days Notes: Use with caution; may cause GI disturbances. Administer on an empty stomach.
Poultry	PO (drinking water)	10-20 mg/kg	q24h	Duration: 3-5 days Notes: Extra-label use only; not approved in many countries. Ensure adequate hydration.

Clinical Indications & Species Uses

General Indications

Treatment of infections caused by susceptible Gram-negative and some Gram-positive bacteria, particularly urinary tract infections

Dog (Canine)

Urinary tract infections (UTIs) caused by susceptible bacteria
Prostatitis
Skin and soft tissue infections (occasionally)
Gastrointestinal infections (e.g., bacterial enteritis)

Cat (Feline)

Urinary tract infections (UTIs)
Skin and soft tissue infections (occasionally)
Gastrointestinal infections (occasionally)

Horse (Equine)

Urinary tract infections
Respiratory tract infections (occasionally)
Skin and soft tissue infections (occasionally)

Cattle (Bovine)

Occasionally used for respiratory and enteric infections in non-lactating animals (extra-label)

Small Ruminants (Sheep / Goat)

Occasionally used extra-label for enteric and respiratory infections

Rabbit & Small Mammals

Urinary tract infections
Respiratory infections (occasionally)
Gastrointestinal infections (occasionally)

Avian & Poultry

Occasionally used extra-label for colibacillosis and other infections

Exotic & Other Species

Reptiles: bacterial infections (occasionally)
Small mammals (e.g., ferrets): urinary and respiratory infections (occasionally)

Pharmacology & Mechanism of Action

Drug Class: Fluoroquinolone antibiotic | Pharmacological Group: Antibacterial

Mechanism of Action: Norfloxacin is a fluoroquinolone antibacterial that inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for DNA replication, transcription, repair, and recombination. By binding to these enzymes, it prevents the supercoiling of bacterial DNA, leading to inhibition of DNA synthesis and ultimately bacterial cell death. It is bactericidal and exhibits concentration-dependent killing.

Pharmacodynamics: Norfloxacin has broad-spectrum activity against many Gram-negative and some Gram-positive bacteria. It is particularly effective against Enterobacteriaceae (e.g., E. coli, Klebsiella, Salmonella, Shigella), and also has activity against Pseudomonas aeruginosa, Haemophilus, and some Mycoplasma. It has moderate activity against staphylococci and streptococci. Its activity is reduced in acidic environments (e.g., urine) and in the presence of divalent cations (e.g., Mg2+, Ca2+, Al3+).

⚡ Pharmacokinetics Summary

Absorption: Norfloxacin is well absorbed after oral administration in most species, but bioavailability can be reduced by food, especially dairy products, and by antacids containing aluminum or magnesium. In dogs, oral bioavailability is approximately 50-70%.

Distribution: Norfloxacin is widely distributed in body tissues and fluids, with high concentrations in the kidneys, urine, prostate, and bile. It penetrates well into the respiratory tract, skin, and soft tissues. It crosses the blood-brain barrier poorly. Protein binding is low to moderate (10-15% in humans).

Metabolism: Norfloxacin undergoes limited hepatic metabolism. It is metabolized to six metabolites, but the parent drug is the primary active form.

Excretion: Norfloxacin is primarily excreted unchanged in the urine via both glomerular filtration and tubular secretion. Biliary excretion also occurs. In animals with renal impairment, dosage adjustment may be necessary.

Half-Life: Dog: 2-3 hours; Cat: 2-4 hours; Horse: 2-4 hours; Cattle: 2-3 hours; Rabbit: 1-2 hours; Poultry: 2-4 hours (varies by species).

Bioavailability: Oral: 50-70% in dogs; reduced by food and divalent cations.

Protein Binding: 10-15% (species-dependent)

Available Formulations & Strengths

Oral Tablet 100 mg, 200 mg, 400 mg (PO)

Oral Solution (veterinary compounded) Various concentrations (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to norfloxacin or other fluoroquinolones
Known cartilage abnormalities or growing animals (especially young dogs and cats) due to risk of arthropathy
Pregnancy and lactation (unless benefit outweighs risk)
Concurrent use with theophylline (increased risk of toxicity)
Use in animals with a history of tendon disorders

Warnings & Clinical Precautions:

Use with caution in young animals (less than 8 months in dogs, less than 12 months in large breed dogs, less than 12 months in cats) due to potential cartilage damage.
Use with caution in animals with renal impairment; dosage adjustment may be necessary.
Avoid concurrent administration with antacids (aluminum/magnesium), sucralfate, iron, zinc, or dairy products as they reduce absorption.
May cause crystalluria; ensure adequate hydration.
Fluoroquinolones can cause CNS stimulation; use with caution in animals with seizure disorders.
In horses, oral administration may be poorly absorbed; other fluoroquinolones are preferred.
Not approved for food animals in many countries; extra-label use requires withdrawal times.
May cause phototoxicity; avoid excessive sunlight exposure during treatment.

Adverse Effects & Reactions

Common:

Gastrointestinal upset (vomiting, diarrhea, anorexia)
Crystalluria (especially in alkaline urine)
Arthropathy in young animals (cartilage damage)

Serious / Severe:

Cartilage erosion and lameness in young animals
CNS stimulation (seizures, agitation)
Acute renal failure (rare)
Tendon rupture (rare)
Hypersensitivity reactions (anaphylaxis)

Rare:

Hepatotoxicity
Blood dyscrasias (leukopenia, thrombocytopenia)
Photosensitivity
Ocular toxicity (with high doses)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Antacids (aluminum/magnesium), sucralfate, iron, zinc	Reduced absorption of norfloxacin due to chelation	High
Theophylline	Increased theophylline levels, risk of toxicity	High
Warfarin	Increased anticoagulant effect	Moderate
Corticosteroids	Increased risk of tendon rupture	Moderate
Nitrofurantoin	Antagonistic effect in urinary tract infections	Moderate
Cyclosporine	Increased risk of nephrotoxicity	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Vomiting
Diarrhea
CNS signs (agitation, seizures, depression)
Crystalluria
Acute renal failure
Cartilage damage in young animals

Emergency Treatment Protocol: Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide supportive care: IV fluids to maintain hydration and promote diuresis. Monitor renal function and CNS status. Seizures may be treated with diazepam or barbiturates. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 5 days🥛 Milk: 3 days🥚 Eggs: 5 days

Withdrawal times are not established for norfloxacin in many countries; these are estimates based on similar fluoroquinolones. Extra-label use in food animals requires extended withdrawal periods; consult regulatory guidelines.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F)

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep in a tightly closed container.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Norfloxacin is not FDA-approved for use in veterinary medicine in the US. It is available for human use, but veterinary use is extra-label. Other fluoroquinolones (e.g., enrofloxacin, marbofloxacin) are approved for animals.

Extra-Label (Off-Label) Use: In the US, extra-label use of fluoroquinolones in food animals is prohibited by the FDA (since 1997) due to concerns about antimicrobial resistance. In other countries, regulations vary; always follow local regulations and consult a veterinarian.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Norfloxacin is a fluoroquinolone antibiotic primarily used for urinary tract infections in small animals. It has good activity against Gram-negative bacteria, including Pseudomonas, but is less effective against Gram-positive organisms. Due to its limited oral bioavailability and the availability of newer fluoroquinolones with better pharmacokinetic profiles (e.g., enrofloxacin, marbofloxacin), norfloxacin is not a first-line choice in veterinary medicine. It is not approved for food animals in many countries, and extra-label use is restricted. When used, it should be administered on an empty stomach, and concurrent administration with divalent cations should be avoided. Monitoring for adverse effects, especially in young animals, is important. Always consider culture and sensitivity testing before initiating therapy.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)