The World Health Organization classifies antimicrobial resistance (AMR) as one of the top 10 global public health threats. Veterinary medicine accounts for a significant proportion of global antimicrobial use, making stewardship essential. Use the Drug Formulary for evidence-based antimicrobial selection and the Pharmacology Specialist for guidance on resistant infections.
Responsible antimicrobial use in veterinary medicine is built on five pillars:
Right Drug: Select the narrowest-spectrum agent effective against the suspected or confirmed pathogen. Avoid empiric use of broad-spectrum or critically important antimicrobials when a first-line agent is appropriate. Culture and sensitivity (C&S) results should guide definitive therapy whenever possible.
Right Dose: Subtherapeutic dosing promotes resistance. Use pharmacokinetic/pharmacodynamic (PK/PD) principles: time-dependent antibiotics (beta-lactams) need frequent dosing to maintain concentrations above MIC, while concentration-dependent agents (fluoroquinolones, aminoglycosides) require high peak concentrations.
Right Route: Use the oral route when bioavailability is adequate. Reserve parenteral therapy for patients unable to tolerate oral medication, those with severe systemic infections, or when tissue penetration requires IV delivery.
Right Duration: Treat for the minimum effective duration. Unnecessarily prolonged courses increase selective pressure. For uncomplicated UTIs, 3-5 days may suffice; for deep pyoderma, 21-28 days or 7 days beyond clinical resolution is standard.
Right De-escalation: Once C&S results return, narrow the spectrum. Switch from IV to oral when the patient is clinically stable. Discontinue antimicrobials promptly when infection is resolved or the diagnosis changes.
The International Society for Companion Animal Infectious Diseases (ISCAID) provides evidence-based guidelines for common infections. Antimicrobials are classified into tiers based on importance to human medicine and resistance potential:
First-Tier (First-Line): Narrow-spectrum agents suitable for empiric therapy. These include amoxicillin, amoxicillin-clavulanate, cephalexin (first-generation cephalosporins), trimethoprim-sulfonamide, and doxycycline. These should be the default choice for most uncomplicated infections.
Second-Tier: Agents reserved for documented resistance to first-tier drugs or specific clinical indications. Includes second- and third-generation cephalosporins (e.g., cefpodoxime, cefovecin), chloramphenicol, and clindamycin in certain contexts.
Third-Tier (Restricted/Critically Important): Fluoroquinolones (enrofloxacin, marbofloxacin, pradofloxacin), carbapenems, vancomycin, and linezolid. These should only be used when C&S confirms no first- or second-tier alternative exists. Fluoroquinolones are classified as Highest Priority Critically Important Antimicrobials by WHO.
Culture and sensitivity testing is essential but not always necessary for every infection. Key indications for C&S include:
Recurrent or relapsing infections, treatment failure after appropriate first-line therapy, deep or life-threatening infections (sepsis, osteomyelitis, pyothorax), infections in sites with poor drug penetration (prostatitis, discospondylitis), any infection where a fluoroquinolone or third-tier agent is being considered, and hospital-acquired infections where resistant organisms are likely.
Warning: Prescribing fluoroquinolones without culture and sensitivity results is a leading driver of resistance. Reserve these agents for documented susceptibility or life-threatening situations where delay in therapy is not acceptable.
| Infection Type | First-Line Antimicrobial | Dose (Dog) | Duration |
|---|---|---|---|
| Uncomplicated UTI | Amoxicillin or TMS | 11-15 mg/kg PO q8h | 3-5 days |
| Superficial pyoderma | Cephalexin or amox-clav | 22-30 mg/kg PO q12h | 21 days or 7d past resolution |
| Deep pyoderma | Cephalexin (culture recommended) | 22-30 mg/kg PO q12h | 28+ days or 14d past resolution |
| Upper respiratory (canine) | Doxycycline | 5 mg/kg PO q12h | 10-14 days |
| Wound infection | Amoxicillin-clavulanate | 12.5-25 mg/kg PO q12h | 7-10 days |
| Otitis externa | Topical (not systemic) | Based on cytology | 14-21 days |
The Drug Formulary provides species-specific dosing, spectrum of activity, and contraindications for all commonly used veterinary antimicrobials.
Prophylactic overuse: Perioperative antimicrobials are indicated only for clean-contaminated, contaminated, or dirty surgical procedures, or clean procedures involving implants. A single preoperative dose (cefazolin 22 mg/kg IV) within 60 minutes of incision is sufficient for most prophylaxis. Continuing antibiotics beyond 24 hours post-operatively for routine clean surgeries provides no benefit and increases resistance.
Too-short courses: Premature discontinuation of antimicrobials is a paradoxical driver of resistance. While the trend is toward shorter courses for some infections (uncomplicated UTI), deep infections and those involving biofilms require full-duration therapy.
Inappropriate broad-spectrum use: Reaching for a fluoroquinolone or third-generation cephalosporin as a first choice is a common trap, especially when empiric therapy feels uncertain. The majority of community-acquired small animal infections respond to first-tier agents.
Antimicrobial resistance does not respect species barriers. MRSA and MRSP are transmitted between pets and humans. Extended-spectrum beta-lactamase (ESBL)-producing E. coli from companion animals have been detected in household contacts. Veterinary prescribing directly influences the resistance landscape in human medicine.
Integrating antimicrobial stewardship into daily practice is not just best medicine for our patients, it is a professional and ethical obligation to protect both animal and human health.
- Apply the 5 R's: Right drug, dose, route, duration, and de-escalation.
- Start with first-tier agents (amoxicillin, cephalexin, doxycycline) for most uncomplicated infections.
- Reserve fluoroquinolones and third-tier agents for culture-confirmed resistant infections.
- Culture before prescribing whenever possible, especially for recurrent, deep, or treatment-resistant infections.
- Antimicrobial resistance is a One Health issue; veterinary prescribing impacts human medicine.
- Use PetMed AI tools for evidence-based antimicrobial selection and specialist consultation.