Enrofloxacin: A Broad Spectrum Antibacterial Drug

Enrofloxacin is a broad-spectrum antibacterial drug belonging to the group of fluoroquinolones. Discovered in 1980, it was one of the earliest fluoroquinolones to be developed and approved for veterinary use.

Chemical Properties and Mechanism of Action
Enrofloxacin contains a bicyclic fluoroquinolone core structure which is responsible for its bactericidal properties. It works by inhibiting the bacterial enzymes DNA gyrase and topoisomerase IV which are required for DNA replication, transcription, repair and recombination. This leads to bacterial cell death. Chemically, enrofloxacin is a white to slightly yellowish crystalline powder. It is very soluble in water and slightly soluble in alcohol and chloroform. Its molecular formula is C19H22FN3O3 and molecular weight is 360.4 g/mol.

Spectrum of Antibacterial Activity
Enrofloxacin has broad spectrum antibacterial activity against both gram-positive and gram-negative bacteria. It is highly effective against respiratory and enteric pathogens like Pseudomonas aeruginosa, Escherichia coli, Salmonella spp., Mycoplasma spp., Actinobacillus pleuropneumoniae and Staphylococcus aureus. It is also active against intracellular pathogens like Chlamydia psittaci. This broad spectrum of activity makes enrofloxacin useful for treating mixed infections in animals.

Approved Veterinary Uses and Dosage Regimens

Mastitis in Dairy Cows
Enrofloxacin is approved for the treatment of clinical and subclinical mastitis caused by susceptible strains of staphylococci and streptococci in dairy cows. The recommended dose is 2.5 mg/kg body weight given as a single intravenous or intramuscular injection. Therapy should continue for at least 5 days after signs of infection have resolved.

Respiratory Infections in Cattle
Enrofloxacin is used to treat respiratory infections in cattle associated with Mannheimia haemolytica, Pasteurella multocida and Histophilus somni. The dose is 5-10 mg/kg body weight given as a single intravenous or intramuscular injection. For more severe cases, treatment may be continued for 3-5 days.

Porcine Respiratory Disease Complex (PRDC) in Pigs (Subsection 3)
Enrofloxacin is a valuable treatment for the bacterial components of PRDC which involve Pasteurella multocida, Actinobacillus pleuropneumoniae and Mycoplasma hyopneumoniae. The recommended dose regimen is 2.5 mg/kg body weight administered intramuscularly or orally once daily for 3-5 days.

Concerns over Effectiveness and Resistance

Emergence of Resistance
With extensive use of enrofloxacin, resistance has emerged among bacterial pathogens. Studies report increasing resistance to enrofloxacin in E. coli, Salmonella spp. and Staphylococcus spp. isolated from food animals. This resistance is usually associated with mutations in bacterial topoisomerase genes. Prudent use of enrofloxacin through judicious prescription is necessary to help slow the spread of resistance.

Reduced Activity against Mycoplasma spp.
There are concerns about reduced effectiveness of enrofloxacin against Mycoplasma infections in animals. Minimum Inhibitory Concentration (MIC) studies show enrofloxacin has low activity against pathogenic mycoplasmas including M. hyopneumoniae and M. synoviae. Therefore, enrofloxacin may not be the ideal choice for treating confirmed mycoplasmal infections in livestock.

Strategies to Prolong Effectiveness
To extend the useful therapeutic life of enrofloxacin, veterinarians should emphasize responsible usage practices. They include using enrofloxacin only when culture and sensitivity testing indicates susceptibility, employing it as a second-line drug when possible and discontinuing treatment after clinical cure. Good hygiene and infection control on farms also helps contain the spread of resistance. Surveillance of resistance patterns aids timely changes to treatment guidelines. With judicious use based on evidence, enrofloxacin can continue providing benefits for animal health.

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