Veterinary CPD webinar – Understanding Antimicrobial Medications for Veterinary Students

Understanding the Basics

Dr. Peters began the session by breaking down some of the core principles that underpin antimicrobial use in veterinary medicine:

• MIC (Minimum Inhibitory Concentration): The lowest concentration of a drug that inhibits bacterial growth in vitro. While not directly predictive of in vivo effectiveness, it provides a valuable benchmark for drug choice.
• Pharmacokinetics vs. Pharmacodynamics:
  • Pharmacokinetics describes what the body does to the drug (absorption, distribution, metabolism, excretion).
  • Pharmacodynamics describes what the drug does to the body—and the pathogen.
• Aerobes vs. Anaerobes: Aerobes thrive in oxygen-rich environments, while anaerobes prefer the absence of oxygen.
• Time-Dependent vs. Concentration-Dependent Antibiotics:
  • Time-dependent drugs rely on how long they stay above the MIC.
  • Concentration-dependent drugs rely on achieving high peak concentrations for efficacy.

Beta-Lactams: The Foundation of Antibiotic Therapy

Dr. Peters reviewed one of the largest and most commonly used antibiotic classes in veterinary practice—beta-lactams, which include:

• Penicillins (e.g., amoxicillin, ampicillin, clavulanic acid combinations)
• Cephalosporins (e.g., cephalexin, cefazolin, cefpodoxime, cefovecin/Convenia)
• Carbapenems (reserved for highly resistant infections)

These drugs are bactericidal and time-dependent, making duration of exposure key to success. However, they are ineffective against organisms without a cell wall (like Mycoplasma).

Dr. Peters highlighted the importance of barrier penetration when selecting a drug—for example, only certain antibiotics reach therapeutic levels in the prostate, eye, or CNS.

Beyond Beta-Lactams: Key Antibiotic Classes to Know

Dr. Peters guided attendees through several other essential antibiotic groups:

Aminoglycosides

• Examples: Gentamicin, Amikacin, Neomycin
• Bactericidal, concentration-dependent, often used topically or via injection.
• Caution: Risk of nephrotoxicity—avoid in patients with renal compromise.

Fluoroquinolones

• Examples: Enrofloxacin (Baytril), Marbofloxacin, Pradofloxacin
• Excellent tissue penetration (including CNS and prostate).
• Avoid in young animals due to potential cartilage damage, and in cats, Enrofloxacin can cause retinal degeneration.

Sulfonamides (TMS)

• Known for excellent tissue penetration and broad activity.
• NAVLE Tip: Can cause permanent KCS (dry eye).

Tetracyclines

• Doxycycline is a mainstay for tick-borne and respiratory diseases.
• Adverse effects: GI upset, enamel discoloration in young animals, and risk of esophageal strictures in cats if not followed by water.

Macrolides & Lincosamides

• Azithromycin, Tylosin, Clindamycin are useful for respiratory infections, Bartonella, and anaerobic abscesses.
• Clindamycin (Antirobe) is particularly valuable for deep oral infections and abscesses.

Antifungals: Navigating Systemic and Topical Options

Dr. Peters also covered common systemic fungal diseases—including blastomycosis, histoplasmosis, cryptococcosis, coccidioidomycosis, and aspergillosis—and the major antifungal drug classes used to treat them:

• Polyenes (Amphotericin B): Highly effective but nephrotoxic; reserved for severe systemic infections.
• Azoles (Ketoconazole, Fluconazole, Itraconazole, Miconazole): Widely used; inhibit ergosterol synthesis.
  • Fluconazole penetrates the CNS and is ideal for fungal meningitis.
  • Ketoconazole can cause endocrine and hepatic side effects.
• Terbinafine (Lamisil): Excellent for dermatophyte infections, often used topically or as a cost-effective oral option.
• Clotrimazole: Used topically for nasal aspergillosis—effective but expensive and must be administered carefully.

Practical Takeaways for Clinical and Exam Success

Dr. Peters closed the webinar with advice for both clinical decision-making and NAVLE® preparation:

• Always consider site penetration and patient immune status when selecting an antimicrobial.
• Use tools like Plumb’s Veterinary Drug Handbook or VIN for dosing, side effects, and interactions.
• Antibiotic stewardship matters—reserve “big gun” antibiotics for resistant infections.
• Expect NAVLE® questions about mechanism of action, adverse effects, and drug class patterns (e.g., “-floxacin” for fluoroquinolones).

Watch the Full Webinar

This blog offers just a snapshot of Dr. Sarah Peters’ detailed session on antimicrobial use.