Study raises concerns about some compounded enrofloxacin ear mixes
Bottom line
A new Auburn University study presented at the 2025 North American Veterinary Dermatology Forum found that not all compounded enrofloxacin ear preparations behave the same once mixed. In the 20-day evaluation, researchers tested 12 compounded otic solutions made with either 100 mg/mL or 22.7 mg/mL enrofloxacin plus different vehicles and add-ins, including sterile water, tris-EDTA, dexamethasone, ketoconazole, and miconazole. Solutions made with sterile water remained compatible and stable, but formulations containing tris-EDTA showed marked concentration loss by day 10, and combinations containing antifungals showed immediate incompatibility, including separation, precipitation, and even an exothermic reaction that prevented drug-strength testing. (navdf2026.com)
Why it matters: Compounded enrofloxacin solutions are commonly used in canine otitis care, especially when clinicians need flexibility beyond labeled products. But this study suggests some widely used combinations may deliver less active drug than intended, or may not remain physically usable after compounding. That matters for treatment response, antimicrobial stewardship, and client communication, particularly when a pet parent is paying for a custom preparation expected to stay effective through the treatment course. Earlier work had suggested enrofloxacin could remain stable for 28 days in some ear-cleaner vehicles, and a 2023 study found enrofloxacin plus saline and dexamethasone remained stable over 28 days, underscoring that the vehicle and additives, not just the drug, drive performance. (navdf2026.com)
What to watch: Watch for a full peer-reviewed publication with complete methods and practical compounding recommendations, especially around whether tris-EDTA or antifungal combinations should be avoided altogether or only under specific formulations. (navdf2026.com)
Key facts
- Study
- Auburn University study presented at the 2025 North American Veterinary Dermatology Forum
- Design
- 20-day evaluation of 12 compounded otic solutions
- Drug
- Enrofloxacin
- Formulations tested
- Baytril 100 mg/mL or Baytril 22.7 mg/mL with sterile water, tris-EDTA, dexamethasone, ketoconazole, or miconazole
- Stable combination
- Sterile-water formulations remained compatible and stable through day 20
- Tris-EDTA finding
- Marked concentration loss by day 10, with precipitate in all tris-EDTA solutions
- Antifungal finding
- Immediate separation, precipitation, and an exothermic reaction
- Methods
- Gross and microscopic evaluation, pH, temperature, HPLC, and mass spectrometry
Compounded enrofloxacin ear medications are a familiar tool in small-animal practice, but new data suggest some common formulations may be far less reliable than clinicians assume. In a 2025 NAVDF abstract, Auburn University investigators reported that enrofloxacin remained compatible and stable in sterile-water formulations over 20 days, while preparations containing tris-EDTA lost substantial drug concentration and those containing antifungals showed immediate incompatibility. (navdf2026.com)
That finding lands in a part of veterinary dermatology where compounding is routine, especially for difficult otitis cases and for practices trying to tailor therapy to cytology, culture results, cost constraints, or patient tolerance. Published background supports how common this is: a 2023 JAAHA study noted that compounded enrofloxacin solutions are often prescribed clinically for bacterial otitis externa, and described typical dilution practices using saline, tris-EDTA, and dexamethasone. (jaaha.kglmeridian.com)
The Auburn team evaluated 12 otic solutions containing either Baytril 100 mg/mL or Baytril 22.7 mg/mL, analyzed on days 0, 10, 15, and 20. They paired enrofloxacin with sterile water, tris-EDTA, sterile water plus dexamethasone sodium phosphate, tris-EDTA plus dexamethasone, tris-EDTA with ketoconazole plus dexamethasone, and miconazole lotion plus dexamethasone. Physical compatibility was assessed by gross and microscopic evaluation, pH, and temperature, while HPLC was used to quantify drug concentration and mass spectrometry was used to evaluate precipitate. (navdf2026.com)
The headline result was the divergence between vehicles. In sterile-water combinations, compatibility and stability were verified through the study period. In tris-EDTA combinations, enrofloxacin concentration had already fallen by day 10 by an average of 25.4% and 29.3% in the 100 mg/mL formulations, and 45.6% and 49.8% in the 22.7 mg/mL formulations, with and without dexamethasone, respectively. Precipitate formed in all tris-EDTA solutions, and filtering that precipitate did not change the measured enrofloxacin concentration, suggesting the instability issue was not simply an artifact of visible solids. In the antifungal-containing formulations, researchers reported immediate separation, precipitation, and an exothermic reaction, which stopped further drug-strength measurement. (navdf2026.com)
The broader literature helps explain why this matters. A 2012 Veterinary Dermatology study found 0.9% enrofloxacin maintained chemical stability and in vitro bactericidal efficacy for 28 days in several ear-cleaner vehicles, including sterile water and tris-EDTA, although one chlorhexidine-containing formulation showed decreased bactericidal efficacy at day 14. More recently, a 2023 study reported that 1% enrofloxacin and 0.3% gentamicin in normal saline with 0.1% dexamethasone remained chemically stable and bactericidally effective over 28 days. And a 2025 Today’s Veterinary Practice review urged clinicians to rely on formulation-specific stability data when compounding ear medications, noting that in vitro interactions during compounding can reduce effectiveness. Taken together, the Auburn findings don't mean compounded enrofloxacin is unreliable across the board; they suggest reliability depends heavily on exactly what it is mixed with. (experts.illinois.edu)
No outside quote reacting specifically to the Auburn abstract was readily available in public sources, but the available expert-oriented commentary points in the same direction: compatibility and stability data should guide compounding decisions, rather than habit or anecdote. That is especially relevant because compounded otic therapy often sits at the intersection of dermatology, pharmacology, and client affordability, where small formulation choices can have outsized clinical consequences. (todaysveterinarypractice.com)
Why it matters: For veterinary professionals, this is a practical reminder that a compounded ear medication is not one interchangeable category. If a preparation loses roughly one-quarter to one-half of its enrofloxacin concentration within 10 days, or becomes physically incompatible on mixing, clinicians may be dealing with underdosing, treatment failure, misleading recheck expectations, and avoidable antimicrobial exposure. It also raises questions for pharmacy communication, beyond-use dating, and whether some combinations that seem pharmacologically appealing, such as pairing enrofloxacin with tris-EDTA or antifungals, may be chemically unsound in real-world use. (navdf2026.com)
What to watch: The next step is a full peer-reviewed paper with complete methods, storage conditions, and formulation ratios, plus any follow-up work linking these compatibility findings to microbiologic efficacy or clinical outcomes. Until then, the safest near-term takeaway is narrow but important: sterile-water enrofloxacin formulations appear supported by these data, while tris-EDTA and antifungal combinations deserve caution, and likely reconsideration, before they’re sent home with a pet parent. (navdf2026.com)