Enrofloxacin

Overview

Enrofloxacin is a fluoroquinolone antimicrobial widely used in veterinary medicine for the treatment of bacterial infections in dogs and cats. It is a concentration-dependent antibiotic with broad-spectrum activity, particularly against Gram-negative organisms.

Enrofloxacin is available in injectable and oral formulations and is characterized by good tissue penetration due to its lipophilic nature. It achieves high intracellular concentrations, making it effective for infections involving soft tissues, skin, and the urogenital tract.

Mechanism of Action (MOA): Enrofloxacin inhibits bacterial DNA gyrase, an essential enzyme involved in DNA replication and transcription. This results in disruption of bacterial DNA processes and leads to rapid bactericidal activity, especially at higher drug concentrations.

Indications

Enrofloxacin is used in dogs and cats for the treatment of bacterial infections, particularly when culture and sensitivity testing indicate susceptibility and when lower-tier antimicrobials are unlikely to be effective.

• Gram-negative and Gram-positive bacterial infections: Active against a wide range of organisms including Escherichia coli, Klebsiella, Proteus, Salmonella, Pasteurella, Staphylococcus, and Pseudomonas aeruginosa.
• Mycoplasma infections: Effective against Mycoplasma species.
• Soft tissue and skin infections: High tissue penetration makes it useful for managing skin and soft tissue infections.
• Urogenital infections: Particularly useful for urinary and prostatic infections due to good distribution into these tissues.
• Mycobacterial infections (non-tubercular): May be used in combination with other antimicrobials (e.g. clarithromycin, rifampin).
• Severe systemic infections: Has been used (off-label) in severe infections such as sepsis when alternative routes or therapies are inadequate.

Dosage (Reference)

Dog

In dogs, enrofloxacin is administered subcutaneously once daily. Dose selection may vary depending on infection severity and site, with higher doses used for difficult-to-treat infections.

Cat

In cats, enrofloxacin can be administered either subcutaneously or orally. Careful dosing is essential due to the risk of retinal toxicity at higher doses.

Warnings & Precautions

Enrofloxacin should be used cautiously in certain patient populations due to potential effects on developing cartilage, the central nervous system, and species-specific toxicity risks.

• Growing animals: Fluoroquinolones are relatively contraindicated in young, growing dogs due to the risk of cartilage abnormalities.
• Age restrictions: Not authorized in dogs less than 1 year of age (or less than 18 months in large-breed dogs) and in cats younger than 8 weeks.
• Cats (retinal toxicity): Use with caution due to risk of irreversible retinal damage; strict adherence to dosing recommendations is essential.
• Seizure disorders: Use cautiously in epileptic animals, as fluoroquinolones may potentiate CNS adverse effects.
• Route of administration: Intravenous use is not authorized; if used in severe cases, the drug must be diluted and administered slowly.

Drug Interactions

Drug interactions with enrofloxacin are primarily related to altered absorption, metabolism, or potentiation of drug effects. Appropriate spacing or avoidance of certain combinations is recommended.

• Antacids and absorbents (Mg²⁺, Al³⁺): Bind enrofloxacin in the gastrointestinal tract and reduce absorption; separate administration by at least 2 hours.
• Sucralfate and zinc salts: Decrease oral absorption; administer at least 2 hours apart.
• Theophylline: Enrofloxacin may increase plasma concentrations, increasing risk of toxicity.
• Cimetidine: May reduce clearance of enrofloxacin, increasing drug exposure.
• Ciclosporin and tacrolimus: May increase nephrotoxicity due to reduced metabolism; concurrent use should be avoided if possible.
• Oral anticoagulants: May enhance anticoagulant effects, increasing bleeding risk.

Side Effects & Overdose

Side Effects

Adverse effects of enrofloxacin are uncommon but may be serious, particularly in cats, and are often dose-related.

• Retinal toxicity (cats): Irreversible blindness has been reported, especially at doses exceeding recommendations, though rare cases may occur even at standard doses.
• CNS effects: Use with caution in epileptic animals due to potential for increased neurologic adverse effects.

Overdose

Overdose of enrofloxacin is most concerning in cats due to dose-dependent retinal toxicity and risk of permanent vision loss.

• Retinal damage: High doses may result in irreversible blindness in cats.
• Management: No specific antidote; supportive care and immediate dose adjustment or discontinuation are required.

Key Notes

Practical clinical points that help optimize the effective and responsible use of enrofloxacin in veterinary patients:

• Concentration-dependent killing: Higher peak concentrations improve antibacterial efficacy, making once-daily dosing strategies effective for many infections.
• Pulse dosing strategy: Intermittent higher-dose regimens may enhance efficacy, particularly against Gram-negative organisms.
• Excellent tissue penetration: High intracellular concentrations make it particularly useful for infections in difficult-to-reach sites such as prostate and deep tissues.
• Poor anaerobic coverage: Limited activity against obligate anaerobes; alternative or combination therapy may be required.
• Antimicrobial stewardship: Should be reserved for cases where culture and sensitivity support its use or when first-line antimicrobials are ineffective.