The domestic rabbit (Oryctolagus cuniculus) possesses a highly specialized gastrointestinal tract that relies on hindgut cecotrophy and a delicate balance of anaerobic, Gram-positive microflora (primarily Bacteroides and Firmicutes) to ferment dietary fiber. Consequently, rabbits are exceptionally sensitive to antimicrobial therapy. Systemic administration of certain antibiotics can disrupt this microflora (dysbiosis), leading to the overgrowth of toxigenic bacteria such as Clostridium spiroforme or Escherichia coli, resulting in rapidly fatal enterotoxemia (typhlitis). In addition to gastrointestinal risks, certain veterinary antibiotics carry systemic toxicities—such as cardiotoxicity—that are unique to exotics.

To evaluate these pharmacovigilance risks, VetMedGuide analyzed a June 2026 public extract of the FDA Center for Veterinary Medicine (CVM) animal adverse-event database, which contains 1.34 million reports. We isolated all reports where the target species was a rabbit and the therapy involved a systemic antibacterial active ingredient — excluding ionophore coccidiostats (e.g., monensin), topical silver sulfadiazine, and ophthalmic/otic preparations that do not represent systemic antibiotic therapy — identifying 105 unique adverse event reports. (For the species-wide antibiotic picture across dogs, cats, and food animals, see our antibiotic and anti-infective FDA adverse-event overview.)

The FDA's standard caveat applies — and it matters especially here: these are spontaneous reports, so they do not establish true event rates or prove causation, and reporting in prey species like rabbits is overwhelmingly skewed toward the worst outcomes (owners and clinics report when a rabbit dies, rarely when a course is simply tolerated). Read as a map of where antibiotic use goes wrong in rabbits rather than as a side-effect rate, the analysis reveals a high case fatality rate among reported events and highlights the critical distinction between gut-tolerated antibiotic classes and contraindicated, high-risk agents.

Reported Case Severity: A High Fatality Signal

Rabbits are prey species that instinctually mask clinical signs of illness until physiological decompensation is advanced. This behavior, combined with the rapid progression of enterotoxemia, is reflected in the high severity of outcomes documented in the FDA database:

• Death: 41 reports (39.0% of all reported antibiotic adverse events)
• Anorexia: 12 reports (11.4%) — a sentinel sign of developing enterotoxemia or GI stasis.
• Diarrhoea: 6 reports (5.7%) — the clinical hallmark of antibiotic-induced clostridial typhlitis.
• Death by Euthanasia: 3 reports (2.9%)

A total of 49 reports documented a fatal outcome (death or euthanasia), representing 46.7% of the entire reported rabbit antibiotic cohort. This high mortality rate indicates that adverse event reporting in exotics is heavily skewed toward severe, fatal cases, and highlights the narrow therapeutic window available when antibiotic-induced complications occur.

Safe vs. Unsafe Antibiotics: The Caseload Breakdown

The 100 reported antibiotic events are distributed across several distinct drug classes, reflecting both their usage frequency and their safety profiles:

Note: Reports can involve multiple drugs or reactions, so classes overlap and do not sum to 105. Enrofloxacin alone accounts for 41 of the 46 fluoroquinolone reports; tilmicosin accounts for 12 of the 17 macrolide reports. Aminoglycosides did not appear as a standalone class in these rabbit reports — consistent with their gut-safe, predominantly parenteral use — though they are discussed below as a clinical option.

1. Enrofloxacin (41 reports)

Enrofloxacin (Baytril) is the most widely prescribed antibiotic in rabbit medicine due to its broad spectrum against Gram-negative pathogens (such as Pasteurella multocida) and its high safety margin regarding the gut.

However, the CVM reports highlight that enrofloxacin is a highly alkaline drug that can cause severe local tissue reactions. The dominant reactions reported for enrofloxacin were injection site pain, irritation, and localized skin necrosis. To mitigate this, injectable enrofloxacin should be diluted with sterile saline or LRS (typically 1:1 or 1:2) and administered subcutaneously rather than intramuscularly, or transitioned to oral administration as soon as clinically feasible.

2. Tilmicosin Phosphate (12 reports)

Tilmicosin (Micotil) is a macrolide antibiotic labeled for bovine and ovine respiratory disease. It has been evaluated off-label in rabbits for the treatment of severe pasteurellosis (snuffles), but it is highly cardiotoxic.

The 12 reports in the database document a severe clinical signature: sudden death, recumbency, convulsions, and cardiac arrest. Tilmicosin induces calcium-channel blockade in cardiac myocytes, producing a negative inotropic effect and fatal arrhythmias. The Micotil label states explicitly that death following exposure to tilmicosin injection has been reported to FDA/CVM in goats, rabbits, pigs, dogs, cats, alpacas, and horses. Systemic use in rabbits is contraindicated; any off-label use for refractory disease belongs in the hands of an exotics specialist, not routine practice.

3. Beta-Lactam Toxicity (Amoxicillin/Clavulanate)

Oral beta-lactam administration is the classic trigger for antibiotic-associated enterotoxemia in rabbits. The database contains 11 reports involving amoxicillin and clavulanate.

Beta-lactams selectively destroy the normal Gram-positive flora of the cecum, allowing Clostridium spiroforme to proliferate and release iota-toxin. This toxin causes severe, often hemorrhagic typhlitis. The clinical presentation in these reports is characterized by rapid onset of anorexia, watery diarrhea, hypothermia, and death within 24 to 72 hours of administration.

Antibiotics to Avoid by the Oral Route in Rabbits

To prevent fatal dysbiosis, exotics clinicians keep a short list of classes that are contraindicated by the oral route in rabbits because they selectively destroy the Gram-positive cecal flora and trigger Clostridium spiroforme overgrowth. The Merck Veterinary Manual names the following as contraindicated for oral administration in rabbits:

• Penicillins — amoxicillin, amoxicillin/clavulanic acid, ampicillin. Exception: injectable penicillin G (procaine or benzathine/procaine combinations) is tolerated because it bypasses direct cecal exposure.
• Lincosamides — clindamycin, lincomycin. High risk of enterotoxemia even at low exposure.
• Macrolides — erythromycin (and related agents such as tylosin). Dysbiosis risk by the oral route.
• Cephalosporins — oral cephalosporins are contraindicated; injectable cefovecin (Convenia) should be used with caution.

Several references also flag tetracyclines and high-dose or prolonged penicillin/streptomycin as capable of inducing dysbiosis. Aminoglycosides, by contrast, are relatively gut-safe because they target Gram-negative aerobes and have little activity against the anaerobic cecal flora the rabbit depends on.

Safe Antibiotic Options for Rabbits

When treating bacterial infections in rabbits, clinicians generally choose from classes that do not disrupt the Gram-positive cecal flora:

• Fluoroquinolones: enrofloxacin, marbofloxacin.
• Potentiated sulfonamides: trimethoprim-sulfadiazine (TMS).
• Chloramphenicol / florfenicol: well tolerated, though chloramphenicol requires careful handling because of human aplastic-anemia risk.
• Aminoglycosides (parenteral): gentamicin, amikacin — relatively gut-safe, used for Gram-negative infections with renal monitoring.
• Parenteral penicillin G (benzathine/procaine): a beta-lactam, but tolerated by injection and effective for dental abscesses and rabbit syphilis (Treponema paraluiscuniculi).

If a rabbit develops soft stool or anorexia during any antibiotic therapy, the medication must be discontinued immediately and the cecal microflora supported. Supportive care should include aggressive fluid therapy, thermal support, assist-feeding with a high-fiber critical care formula (e.g., Oxbow Critical Care), and gastrointestinal prokinetics (e.g., metoclopramide or cisapride) as directed by a veterinarian.

Sources

• FDA Center for Veterinary Medicine (CVM), animal adverse-event database (public extract dated June 9, 2026; 1.34 million reports); analysis by VetMedGuide of 100 reports naming an antibiotic active ingredient in rabbits. The FDA cautions that spontaneous reports do not establish causation or true event rates. https://www.fda.gov/animal-veterinary/safety-health/reporting-animal-drug-and-device-side-effects-and-product-problems
• Micotil 300 (tilmicosin phosphate injection) label, DailyMed, NADA 140-929 (boxed warning: death following exposure reported in goats, rabbits, pigs, dogs, cats, alpacas, horses; cardiovascular toxicity consistent with calcium-channel blockade). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=08f1aecd-33c2-457b-8a45-c38fafb3a1c7
• FDA Center for Veterinary Medicine. Animal Drug Safety Communication: Micotil 300 Labeling Change (December 13, 2022). https://www.fda.gov/animal-veterinary/cvm-updates/fda-animal-drug-safety-communication-micotil-300-labeling-change
• Merck Veterinary Manual. Management of Rabbits — Therapeutics in Rabbits (antibiotics contraindicated for oral use). https://www.merckvetmanual.com/exotic-and-laboratory-animals/rabbits/management-of-rabbits
• MSD Veterinary Manual. Bacterial and Mycotic Diseases of Rabbits (enterotoxemia; C. spiroforme iota toxin; oral beta-lactams, lincomycin, clindamycin, erythromycin contraindicated). https://www.msdvetmanual.com/exotic-and-laboratory-animals/rabbits/bacterial-and-mycolic-diseases-of-rabbits