Veterinary 2025 Guide: Penicillin Use in Dogs & Cats 🐾🩺

Hello, I’m Dr Duncan Houston BVSc. In this guide, we explore the various forms of penicillin antibiotics—including penicillin G, ampicillin, and amoxicillin/phosphate combinations—used to treat bacterial infections in dogs and cats. We’ll discuss formulations, mechanisms, dosing, side effects (especially allergic reactions), antibiotic stewardship, monitoring, and owner education, supported by Ask A Vet tools 😊.

🔍 1. What Is Penicillin?

Penicillin is a β‑lactam antibiotic originally derived from *Penicillium* fungi. It works by inhibiting bacterial cell wall synthesis, causing bacterial death :contentReference[oaicite:3]{index=3}.

🎯 2. Common Veterinary Forms

• Penicillin G: injectable (procaine or potassium salts); used in dogs/cats for respiratory, skin, abscess, dental, and urinary infections :contentReference[oaicite:4]{index=4}.
• Ampicillin: injectable and occasionally oral; ideal for respiratory, skin, and leptospirosis treatments :contentReference[oaicite:5]{index=5}.
• Amoxicillin or amoxicillin‑clavulanate: oral forms widely used for skin, urinary, and GI infections; clavulanate extends spectrum :contentReference[oaicite:6]{index=6}.

💊 3. Dosing & Administration

• Penicillin G: dose per label/injection; given by a veterinarian via IM/IV (cats and dogs) :contentReference[oaicite:7]{index=7}.
• Ampicillin injection: usually given in-hospital; oral version less common due to absorption concerns :contentReference[oaicite:8]{index=8}.
• Oral amoxicillin: often given at 10–20 mg/kg BID or TID; amoxicillin/clavulanate uses same dose :contentReference[oaicite:9]{index=9}.
• Administer with food if GI upset occurs, though most are well-absorbed on an empty stomach.
• If dose is missed, skip it and continue scheduled dosing—do **not** double doses.

⚠️ 4. Side Effects & Allergy Risk

• GI upset: vomiting, diarrhea, reduced appetite—mild and usually manageable :contentReference[oaicite:10]{index=10}.
• Allergic reactions: ranging from skin rashes to anaphylaxis; more common in penicillin-sensitive pets (<1%) :contentReference[oaicite:11]{index=11}.
• Neurological signs: seizures or tremors may occur rarely with toxicity :contentReference[oaicite:12]{index=12}.
• Superinfection: disrupting normal flora can allow yeast or *Clostridioides difficile* overgrowth :contentReference[oaicite:13]{index=13}.

🔄 5. Antimicrobial Stewardship

• Reserve penicillins for confirmed or strongly suspected susceptible infections.
• Use culture and sensitivity testing when resistance is suspected or recurrence occurs.
• Prefer narrow-spectrum agents unless broad coverage is needed; switch to narrow-spectrum asap :contentReference[oaicite:14]{index=14}.
• Complete full course—even if symptoms resolve early—to prevent resistance.

📋 6. Monitoring & Follow‑Up

• Check for resolution of infection signs—fever, discharge, malaise—within 48–72 hrs; extend or change therapy if no improvement.
• Schedule recheck appointments for difficult infections; repeat cytology or culture as needed.
• Monitor for adverse reactions — especially skin or GI symptoms.

📝 7. Client Education & Home Care

• Explain formulation differences and why the vet chose injectable vs. oral forms.
• Demonstrate safe administration and dosing reminders.
• Warn about allergy signs—hives, swelling, breathing issues—indicate urgent care.
• Encourage use of Ask A Vet app for pill reminders, side-effect tracking, and vet messaging 😊.

📌 8. 2025 Vet Takeaways

• Penicillins remain essential frontline antibiotics—safe, effective, and narrow-spectrum.
• Use penicillin G for injectable therapy; ampicillin/ amoxicillin for oral infections.
• Allergy risk is low but serious—educate clients accordingly.
• Antimicrobial stewardship is crucial: target therapy and complete full course.
• Digital support tools like Ask A Vet help improve adherence and safety 😊.

At Ask A Vet, we offer dosing calculators, reminders, stewardship alerts, and 24/7 veterinary messaging to support safe, effective antibiotic use. Encourage owners to download our app for peace of mind and optimal outcomes ❤️