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Enrofloxacin / Baytril

Antimicrobial Agents
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Tablets: 5.7 mg, 22.7 mg, 68 mg, & 136 mg

Can be made into suspension.

Also comes as 22.7 mg/mL in 20 mL vials, or 5% solution in 20 mL vials for injection.


Enrofloxacin, a second-generation1 fluoroquinolone, is a broad-spectrum, concentration dependent bactericidal antibiotic with significant post-antibiotic effect (meaning it lends itself to once-daily application of the total daily dose or pulse-dosing regimens where deemed appropriate). The mechanism of action is believed to inhibit bacterial DNA-gyrase, prevent DNA supercoiling and synthesis.

It has activity against some Gram-positive aerobes such as staphylococci, and a wide range of Gram-negative bacilli and cocci, which include klebsiella spp., pasteurella spp., pseudomonas spp., salmonella, and other organisms such as mycoplasma, and chlamydia.

Because the fluoroquinolones have shown variable activity against most Streptococci, as well as weak activity against many anaerobic bacteria, they are not generally recommended for use in treating these types of infections.

When taken orally enrofloxacin is well absorbed, and although the presence of food in the stomach may delay rate it does not seem to affect its absorption capability.

Enrofloxacin is well distributed throughout the body, and can be found in small concentrations in the cerebral spinal fluid. About 30-40% of the drug is metabolized to the human approved drug, ciprofloxacin.

Enrofloxacin is eliminated by both renal and hepatic mechanisms, as well as in breast milk.

It is known that the quinolone class of drugs have been shown to produce erosions of articular cartilage in weight bearing joints, as well as producing other signs of arthropathy in immature animals of various species, including juvenile rats (Kashida et al., 1997). However, evidence of cartilage abnormalities appear to be dose related (high dosages over extended period).

It is also important to note that although the use of fluoroquinolones have not been recommended for initial treatment in pregnant and nursing does or juvenile rats (under 4 months) due to the risks of cartilage abnormalities (Egerbacher et al., 2000), in cases where other antibiotics are not helping, or if the infection is deemed severe, the benefit of using fluoroquinolones (alone or in combination with other compatible antimicrobials) may, in fact, outweigh the risks.

Studies reported by Bayer, in their insert for enrofloxacin, reveal no evidence of carcinogenic or teratogenic effects in rats at higher doses of up to 50mg/kg.

Refer to Baytril insert by Bayer: http://www.bayerdvm.com/products/baytril/baytril.cfm


Useful in: respiratory infections, urinary tract infections, soft tissue infection and soft tissue injury.

Drug Interactions or Contraindications

Concurrent administration of a quinolone, including enrofloxacin, with cation-containing GI products such as magnesium/aluminum antacids or sucralfate, or GI products containing calcium, iron, or zinc may reduce its absorption. It is suggested to separate dosing from any of these products by 2 hours.

Theophylline blood levels may be increased when used with enrofloxacin.

Probenecid blocks tubular secretion of enrofloxacin and may cause an increase in its blood level and half life.

Synergism can occur when aminoglycosides, cephalosporins, and extended-spectrum penicillins are used with fluorinated quinolones such as enrofloxacin.

Adverse Reactions

CNS: restlessness, seizures

GI:  decreased appetite, diarrhea

GU:  crystalluria

Skin:  Can cause tissue damage when given undiluted in IM or SQ injections in pet rats.

Other:  itching

Dosage Recommendations

*Note: If choosing to use Baytril 10%, keep in mind it has a concentration of 100 mg per 1 mL.
Also, because the injectable can be so caustic to tissue it must be diluted for all routes.

5 mg/kg to 20 mg/kg, PO, SQ, IM, q12hr; combine with doxycycline for Mycoplasma in rats. 34


5 mg/kg to 10 mg/kg, PO, IM, q12hr  1 26 27 28; anywhere from 5 to 30 days (injectable form may be given orally). May be combined with doxycycline for treatment of mycoplasma. 26 27


5 mg/kg to 20 mg/kg, PO, SQ, q24hr  26 27


10 mg/kg to 20 mg/kg, PO, SQ, IM, q24hr: Caution with SQ or IM injection as these routes can cause tissue necrosis and pain at the site. Dilute with sterile saline before injection. 38


5 mg/lb, PO, BID (as recommended on RMCA Drug Chart4

Enrofloxacin in Treatment Regimen

The following dosage guideline, for use of enrofloxacin in rats with serious respiratory infection suspected to have Mycoplasma as the pathogen, is recommended by Dr. Michael Hutchinson, DVM; Animal General, Cranberry Township, PA. 18 , and is based on his experience treating rats and current literature:

    Enrofloxacin at 15 mg/kg, PO (oral), q12hr, for 10 to 30 days: directly related to severity of illness.

    Treatment is initiated early, and aggressively, starting with 15 mg/kg for 10 days followed by assessment of the rat’s progress, and may be continued at that dose based on veterinary discretion.

    For initial or repeated respiratory infection unresponsive to enrofloxacin alone or when modeerate, serious to advanced lung infection is present, treatment regimen incorporating enrofloxacin (Baytril) 15 mg/kg, PO, q12hr, along with doxycycline, nebulized agents (Gentocin and albuterol), and dexamethasone can be initiated. For information on Dr.Hutchinson’s treatment regimen see articles: Mycoplasma or Pneumonia in the Health section of the Rat Guide.

    Because Mycoplasma is probably never eliminated entirely from the airways, it often becomes necessary to use pulse antibiotic therapy (long term, intermittent, dosing), or a continuing maintenance schedule of antibiotics for rats with chronic Mycoplasmosis.

    Dr. Hutchinson has had some success with the long term, maintenance dosing of enrofloxacin 15 mg/kg, q12hr, PO (or in the presence of renal disease 8 mg/kg to 10 mg/kg, q12hr) in conjunction with doxycycline 5 mg/kg to 10 mg/kg, q12hr, PO, and based on his experience no discernible side effects have been noted.

    For appropriate dosing in pulse antibiotic therapy for chronic illness, discuss with veterinarian

Note: see warning for young, pregnant or nursing rats in Pharmacology section above.


  • Because enrofloxacin may cause skin ulceration (tissue necrosis), and pain, at the injection site; when giving SQ, or IM, it is recommended to dilute the injectable solution with sterile saline or LRS.  1  34,38
  • Be sure to keep animals well hydrated to prevent crystalluria (formation of crystals in urine).
  • Reconstituted suspension from powder should be kept refrigerated and has a 14 day expiration time.
  • Injectable Baytril should be stored away from direct sunlight. Do not refrigerate the injectable form, freeze or store at or above 40°C (104°F). Precipitation may occur at cold temperature. To redissolve, warm and then shake the vial.
  • Enrofloxacin can be used simultaneously with doxycycline in the treatment of Mycoplasma. 26 27

    Also, in treating suspected polymicrobial infections, where a broader coverage may be needed, synergistic or combination drugs may be used. The following drugs may be seen used simultaneously with enrofloxacin: aminoglycosides (e.g., amikacin or gentamicin), or aminopenicillins (e.g., amoxicillin or ampicillin), or third generation cephalosporins, or clindamycin, or doxycycline (for mycoplasma), or metronidazole.  1

  • Please note that it is imperative to discuss the changing or adding of any medications during your rat’s treatment with your veterinarian to prevent future resistance of microbes to the drugs prescribed.
  • Egerbacher, M., Seiberl, G., Wolfesberger, B., & Walter, I. (2000). Ciprofloxacin causes cytoskeletal changes and detachment of human and rat chondrocytes in vitro. Arch Toxicol, 73(10-11), 557-63. Retrieved December 20, 2008, from the PubMed database.
  • Pallo-Zimmerman, L., Byron, J., & Graves, T. (July 2010). Fluoroquinolones: Then and Now. Vetlearn.com. Retrieved April 25, 2011, from www.vetlearn.com/Portals/0/PV0710_zimmerman_CE.pdf
  • Kashida Y, Kato M. Toxic effects of quinolone antibacterial agents on the musculoskeletal system in juvenile rats. Toxicol Pathol 1997;25:635-43. Retrieved 2011.
1. Amended to second-generation; 2011 (kg);

Posted on June 23, 2003, 14:17, Last updated on May 15, 2017, 16:25 | Antimicrobial Agents

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