Enrofloxacin and butyl alcohol

Indications

Baytril (brand of enrofloxacin) Injectable Solution is indicated for the management of diseases in dogs associated with bacteria susceptible to enrofloxacin. EFFICACY CONFIRMATION: Clinical efficacy was established in dermal infections (wounds and abscesses) associated with susceptible strains of Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus intermedius, respiratory infections (pneumonia, tonsillitis, rhinitis) associated with susceptible strains of Escherichia coli and Staphylococcus aureus; and urinary cystitis associated with susceptible strains of Escherichia coli, Proteus mirabilis, and Staphylococcus aureus.

Dosage and Administration

Baytril Injectable Solution may be used as the initial dose at 2.5 mg/kg. It should be administered intramuscularly (IM) as a single dose, followed by initiation of Baytril Tablet therapy. Baytril Injectable Solution may be administered as follows: *The initial Baytril Injectable administration should be followed 12 hours later by initiation of Baytril Tablet therapy. Weight of Animal Baytril Injectable Solution* 2.5 mg/kg 9.1 kg (20 lb) 1.00 mL 27.2 kg (60 lb) 3.00 mL The lower limit of the dose range was based on efficacy studies in dogs where enrofloxacin was administered at 2.5 mg/kg twice daily. Target animal safety and toxicology studies were used to establish the upper limit of the dose range and treatment duration.

Contraindications

Enrofloxacin is contraindicated in dogs known to be hypersensitive to quinolones. Based on the studies discussed under the section on Animal Safety Summary, the use of enrofloxacin is contraindicated in small and medium breeds of dogs during the rapid growth phase (between 2 and 8 months of age). The safe use of enrofloxacin has not been established in large and giant breeds during the rapid growth phase. Large breeds may be in this phase for up to one year of age and the giant breeds for up to 18 months. In clinical field trials utilizing a daily oral dose of 5.0 mg/kg, there were no reports of lameness or joint problems in any breed. However, controlled studies with histological examination of the articular cartilage have not been conducted in the large or giant breeds.

Warnings

For use in animals only. The use of this product in cats may result in Retinal Toxicity. Keep out of reach of children. Avoid contact with eyes. In case of contact, immediately flush eyes with copious amounts of water for 15 minutes. In case of dermal contact, wash skin with soap and water. Consult a physician if irritation persists following ocular or dermal exposure. Individuals with a history of hypersensitivity to quinolones should avoid this product. In humans, there is a risk of user photosensitization within a few hours after excessive exposure to quinolones. If excessive accidental exposure occurs, avoid direct sunlight. For customer service or to obtain product information, including Safety Data Sheet, call 888-545-5973.

Precautions

Quinolone-class drugs should be used with caution in animals with known or suspected Central Nervous System (CNS) disorders. In such animals, quinolones have, in rare instances, been associated with CNS stimulation which may lead to convulsive seizures. Quinolone-class drugs have been associated with cartilage erosions in weight-bearing joints and other forms of arthropathy in immature animals of various species. The use of fluoroquinolones in cats has been reported to adversely affect the retina. Such products should be used with caution in cats.

Adverse Reactions

No drug-related side effects were reported in 122 clinical cases treated with Baytril (enrofloxacin) Injectable Solution followed by Baytril Tablets at 5.0 mg/kg per day.

Description

Enrofloxacin is a synthetic chemotherapeutic agent from the class of the quinolone carboxylic acid derivatives. It has antibacterial activity against a broad spectrum of Gram negative and Gram positive bacteria (See Tables I and II ). Each mL of injectable solution contains: enrofloxacin 22.7 mg, n-butyl alcohol 30 mg, potassium hydroxide for pH adjustment and water for injection, q.s. CHEMICAL NOMENCLATURE AND STRUCTURAL FORMULA: 1-cyclopropyl-7-(4-ethyl-1-piperazinyl)-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid. Structural Formula ACTIONS: Microbiology: Quinolone carboxylic acid derivatives are classified as DNA gyrase inhibitors. The mechanism of action of these compounds is very complex and not yet fully understood. The site of action is bacterial gyrase, a synthesis promoting enzyme. The effect on Escherichia coli is the inhibition of DNA synthesis through prevention of DNA supercoiling. Among other things, such compounds lead to the cessation of cell respiration and division. They may also interrupt bacterial membrane integrity. 1 Enrofloxacin is bactericidal, with activity against both Gram negative and Gram positive bacteria. The minimum inhibitory concentrations (MICs) were determined for a series of 37 isolates representing 9 genera of bacteria from natural infections in dogs, selected principally because of resistance to one or more of the following antibiotics: ampicillin, cephalothin, colistin, chloramphenicol, erythromycin, gentamicin, kanamycin, penicillin, streptomycin, tetracycline, triple sulfa and sulfa/trimethoprim. The MIC values for enrofloxacin against these isolates are presented in Table I . Most strains of these organisms were found to be susceptible to enrofloxacin in vitro but the clinical significance has not been determined for some of the isolates. The susceptibility of organisms to enrofloxacin should be determined using enrofloxacin 5 mcg disks. Specimens for susceptibility testing should be collected prior to the initiation of enrofloxacin therapy. TABLE I — MIC Values for Enrofloxacin Against Canine Pathogens (Diagnostic laboratory isolates, 1984) Organisms Isolates MIC Range (mcg/mL) Bacteroides spp. 2 2 Bordetella bronchiseptica 3 0.125-0.5 Brucella canis 2 0.125-0.25 Clostridium perfringens 1 0.5 Escherichia coli 4 <0.016-0.031 Klebsiella spp. 10 0.031-0.5 Proteus mirabilis 6 0.062-0.125 Pseudomonas aeruginosa 4 0.5-8 Staphylococcus spp. 5 0.125 The inhibitory activity on 120 isolates of seven canine urinary pathogens was also investigated and is listed in Table II . TABLE II — MIC Values for Enrofloxacin Against Canine Urinary Pathogens (Diagnostic laboratory isolates, 1985) Organisms Isolates MIC Range (mcg/ mL) E coli 30 0.06-2.0 P. mirabilis 20 0.125-2.0 K. pneumoniae 20 0.06-0.5 P. aeruginosa 10 1.0-8.0 Enterobacter spp. 10 0.06-1.0 Staph, (coag. +) 20 0.125-0.5 Strep, (alpha hemol.) 10 0.5-8.0 Distribution in the Body: Enrofloxacin penetrates into all canine tissues and body fluids. Concentrations of drug equal to or greater than the MIC for many pathogens (See Tables I , II and III ) are reached in most tissues by two hours after dosing at 2.5 mg/kg and are maintained for 8-12 hours after dosing. Particularly high levels of enrofloxacin are found in urine. A summary of the body fluid/tissue drug levels at 2 to 12 hours after dosing at 2.5 mg/kg is given in Table III . TABLE III — Body Fluid/Tissue distribution of Enrofloxacin in Dogs Single Oral Dose = 2.5 mg/kg (1.13 mg/lb) Post-treatment Enrofloxacin Levels Canine (n=2) Body Fluids (mcg/mL) 2 Hr. 8 Hr. Urine 43.05 55.35 Eye Fluids 0.53 0.66 Whole Blood 1.01 0.36 Plasma 0.67 0.33 Tissues (mcg/g) Hematopoietic System Liver 3.02 1.36 Spleen 1.45 0.85 Bone Marrow 2.10 1.22 Lymph Node 1.32 0.91 Urogenital System Kidney 1.87 0.99 Bladder Wall 1.36 0.98 Testes 1.36 1.10 Prostate 1.36 2.20 Uterine Wall 1.59 0.29 Gastrointestinal and Cardiopulmonary Systems Lung 1.34 0.82 Heart 1.88 0.78 Stomach 3.24 2.16 Small Intestine 2.10 1.11 Other Fat 0.52 0.40 Skin 0.66 0.48 Muscle 1.62 0.77 Brain 0.25 0.24 Mammary Gland 0.45 0.21 Feces 1.65 9.97 Pharmacokinetics: In dogs, the absorption and elimination characteristics of the oral formulation are linear (plasma concentrations increase proportionally with dose) when enrofloxacin is administered at up to 11.5 mg/kg, twice daily. 2 Approximately 80% of the orally administered dose enters the systemic circulation unchanged. The eliminating organs, based on the drug's body clearance time, can readily remove the drug with no indication that the eliminating mechanisms are saturated. The primary route of excretion is via the urine. The absorption and elimination characteristics beyond this point are unknown. Saturable absorption and/or elimination processes may occur at greater doses. When saturation of the absorption process occurs, the plasma concentration of the active moiety will be less than predicted, based on the concept of dose proportionality. Following an oral dose in dogs of 2.5 mg/kg (1.13 mg/lb), enrofloxacin reached 50% of its maximum serum concentration in 15 minutes and peak serum level was reached in one hour. The elimination half-life in dogs is approximately 2 ½ -3 hours at that dose. A graph indicating the mean serum levels following a dose of 2.5 mg/kg (1.13 mg/lb) in dogs (oral and intramuscular) is shown in Figure 1 . Figure 1 - Serum Concentrations of Enrofloxacin Following a Single Oral or Intramuscular Dose at 2.5 mg/kg in Dogs. Breakpoint: Based on pharmacokinetic studies of enrofloxacin in dogs after a single oral administration of 2.5 mg enrofloxacin/kg BW (i.e. half of the lowest-end single daily dose range) and the data listed in Tables I and II , the following breakpoints are recommended for canine isolates. Zone Diameter (mm) MIC (μg/mL) Interpretation ≥ 21 ≤ 0.5 Susceptible(S) 18-20 1 Intermediate (I) ≤ 17 ≥ 2 Resistant (R) A report of “Susceptible” indicates that the pathogen is likely to be inhibited by generally achievable plasma levels. A report of "intermediate" is a technical buffer and isolates falling into this category should be retested. Alternatively the organism may be successfully treated if the infection is in a body site where drug is physiologically concentrated. A report of “resistant” indicates that the achievable drug concentrations are unlikely to be inhibitory and other therapy should be selected. Standardized procedures require the use of laboratory control organisms for both standardized disk diffusion assays and standardized dilution assays. The 5 μg enrofloxacin disk should give the following zone diameters and enrofloxacin powder should provide the following MIC values for reference strains. QC strain MIC (μg/mL) Zone Diameter (mm) E. coli ATCC 25922 0.008 - 0.03 32 - 40 P. aeruginosa ATCC 27853 1 - 4 15- 19 S. aureus ATCC 25923 27 - 31 S. aureus ATCC 29213 0.03 - 0.12 Figure 1

Storage

Protect from direct sunlight. Do not freeze. Store at or below 25°C (77°F), excursions permitted up to 40°C (104°F). Use within 90 days of first puncture and puncture a maximum of 20 times. Any product remaining after 20 punctures or more than 90 days after initial puncture should be discarded.

FDA adverse event reports

The FDA Center for Veterinary Medicine publishes the adverse event reports it receives through openFDA. The counts below are the reports naming enrofloxacin and butyl alcohol as an active ingredient for each species this label names, as returned on 2026-09-16, coded by the VeDDRA reaction term the reporter chose. Reactions are counted per report, so one report can appear under several terms.

These are counts, not rates. Reporting is voluntary, the number of animals treated is not known, and a widely used product accumulates reports for that reason alone. A report records that an event followed a dose; it does not establish that the product caused it. The counts say nothing about how one product compares with another.