Antibiotics Use
By Astrid Kruse, DVM
Antibiotics save lives when used correctly to treat bacterial infection, but they can also kill. Proper selection is important, especially for rabbits and other little herbivores with sensitive guts. Some antibiotics can never be used safely in these species — for instance oral penicillin type drugs (e.g., amoxicillin, Clavamox) and drugs like clindamycin. These can cause an often-fatal diarrhea because they kill off the good bacteria in the intestines, which normally control the growth of the dangerous bugs all guts have lying in wait.
Ideally, using an antibiotic would be based on culture results. The veterinarian gets a sample of the infected goo (e.g., urine, nasal secretion, deep ear canal, brains, etc.), and the lab grows the bacteria on a dish, adds bits of different antibiotics, and then the vet can tell which antibiotic will kill that specific bacteria. Your vet combines this information with the knowledge of what antibiotics work well to penetrate the infected area, and what medications your bunny can tolerate.
There are barriers to getting cultures every time. It takes 3-5 days for culture results to be ready, because no one can make bacteria grow faster than this. This means that during that lag time, if the bunny is sick enough (and just about all sick bunnies are sick enough!), the vet needs to make an educated guess and pick an antibiotic to use in the interim. Also, some tissues are hard to culture — it’s difficult to stick a swab high up into the nose without sedation, the deep ear is just about unreachable without a surgical approach, the central nervous system’s brain and spinal cord are frightening places to get close to, abscess goo usually doesn’t have live bacteria anymore and you need a piece of the abscess capsule, which needs to be retrieved surgically. Third, the cost of a culture can be prohibitive to some pet parents, which can be anywhere from one to several hundred dollars.
So often veterinarians are forced to do their best using their experience and what research is available. For upper respiratory infections, I usually start with trimethoprim sulfa or enrofloxacin (Baytril). My second choices are chloramphenicol or rarely doxycycline. For my last resorts I save injectable penicillin and azithromycin — those carry the greatest risk of dysbiosis (killing off the normal gut bacteria), and I have seen several cases of fatal anaphylactic reactions to injectable penicillin. I have been reluctant to try Convenia, an injectable cephalexin type drug used frequently in dogs and cats, as I have heard of some bad reactions in herbivores. For urinary tract infections, I usually use trimethoprim sulfa and sometimes Baytril, or chloramphenicol, or injectable penicillin. For abscesses (a collection of pus in the tissues of the body, often accompanied by swelling and inflammation and frequently caused by bacteria) — in an effort to avoid surgery, for use before surgery, or if surgery isn’t a good option — I will try a combination of metronidazole and enrofloxacin, or chloramphenicol, trimethoprim sulfa, or injectable penicillin.
I have been lucky in that a fair number of abscesses in my patients resolve without surgery. However, I caution that abscesses in my experience go into remission and are possibly never completely cured with medication alone. Surgical removal can be curative, especially if it is a single abscess from a known traumatic event.
All antibiotics have their risks and benefits. For instance, Baytril should be avoided if possible, in young growing rabbits since it can cause cartilage damage in these patients. Baytril also is more likely to have bacterial resistance develop. Chloramphenicol can cause dangerous bone marrow issues in some humans who handle it, so people should wear gloves. Injectable penicillin and azithromycin can seriously disrupt the gut bacteria. And any medication has the potential for causing a reaction, potentially fatal, in any individual patient, and should be used judiciously. So, if your bunny is sick, please take him/her to a rabbit experienced veterinarian. Discuss if a culture is possible. Antibiotics are prescribed when necessary, and make sure you follow the directions on dosing and frequency to avoid overdoses, which can cause illness, and underdosing, which can cause bacterial resistance and make the medication ineffective. And remember that although your vet wants to be a miracle worker, it heartbreakingly isn’t always possible to successfully treat a bacterial infection.