By Dr. Michelle Frye, DVM · Published 2026-05-01
TL;DR. Amoxicillin is a penicillin antibiotic; Clavamox adds clavulanic acid to defeat resistant bacteria. Used for skin, urinary, dental, and respiratory infections. Give with food. Finish the entire course. Refrigerate the Clavamox liquid and toss it after 10 days. Do not buy fish-tank versions for your dog.
The Antibiotic Conversation You've Probably Had
Half the antibiotic conversations I have in the exam room start with: "Doc, last time he had something like this you gave us amoxicillin and it cleared right up." Sometimes that's true. Sometimes the dog had a viral cough. Sometimes the dog had a self-resolving GI bug. And sometimes the previous antibiotic worked for the wrong reason — coincidence dressed up as causation.
Amoxicillin and its augmented sibling Clavamox are everyday drugs in veterinary medicine. They are also among the most overprescribed. Here's how to use them right.
What Amoxicillin and Clavamox Actually Do
Amoxicillin is a beta-lactam antibiotic that disrupts bacterial cell-wall synthesis. Clavamox combines amoxicillin with clavulanic acid, which deactivates the bacterial enzymes (beta-lactamases) that would otherwise destroy the amoxicillin. Result: Clavamox covers a broader spectrum and many resistant strains.
- Typical dog dose: 12.5–25 mg/kg amoxicillin twice daily; Clavamox dosed by the combined formulation.
- Typical cat dose: 12.5 mg/kg twice daily for Clavamox.
- Onset: clinical improvement within 24–48 hours for susceptible infections.
- Course length: 7–14 days for soft tissue / urinary; 21+ days for deep skin and dental.
- Refrigerate the liquid; discard after 10 days.
Things People Are Wrong About
Myth 1: "Fish-grade amoxicillin is the same." Aquarium amoxicillin is unregulated, often subpotent, and not labeled for vertebrate medicine. It is also an absolute red flag with your veterinarian. Don't.
Myth 2: "He's better, I'll save the rest for next time." Stopping early is the leading cause of antibiotic resistance and recurrent infection. Finish the course. The drug doesn't stay good in the cabinet for next time, either.
Myth 3: "It treats kennel cough." Kennel cough is mostly viral or caused by Bordetella, where doxycycline is more appropriate. Most uncomplicated kennel cough resolves on its own.
Myth 4: "Allergic dogs need antibiotics constantly." No. Many recurrent skin infections in allergic dogs need allergy management (Apoquel, Cytopoint, immunotherapy, medicated shampoo) more than they need another round of antibiotic. Antibiotic-only management drives resistance.
When NOT to Use Amoxicillin / Clavamox
Avoid in pets with a documented penicillin or cephalosporin allergy. Use cautiously in pets with significant kidney disease. Do not use to treat viral or fungal infections. For deep, chronic, or recurrent infections, ask your veterinarian about a culture and sensitivity test before another empirical course — the right antibiotic at the right dose is faster and cheaper than three wrong rounds.
What I Tell Owners After 30 Years
Amoxicillin and Clavamox remain great drugs for the right infections. The mistake I see most often is using them for the wrong reason — the cough that wasn't bacterial, the diarrhea that didn't need an antibiotic, the recurring hot spot that actually needs allergy control. When they're indicated, give them with food, give the whole course, and let them work. When they're not, more antibiotic isn't the answer.
Frequently Asked Questions
Can I give my dog human amoxicillin?
Veterinary and human amoxicillin contain the same active ingredient, but dosing must be calculated specifically for your pet by your veterinarian. Do not self-prescribe. Pediatric amoxicillin liquid often contains additives that may not suit your pet.
How long does amoxicillin take to work?
Clinical improvement is usually visible within 24–48 hours for susceptible infections. The course must still be finished as prescribed.
What is the difference between amoxicillin and Clavamox?
Clavamox combines amoxicillin with clavulanic acid, which inactivates the enzymes some bacteria use to destroy amoxicillin. Clavamox covers a broader spectrum, including many resistant skin and urinary infections.
Should I give amoxicillin with food?
Yes. Giving with food significantly reduces the risk of vomiting and decreased appetite.
Why do I need to refrigerate Clavamox liquid?
The reconstituted Clavamox suspension is unstable at room temperature. Refrigerate immediately and discard after 10 days, even if some remains.
Can amoxicillin treat a UTI in my dog?
It can — but resistant bacteria are increasingly common in canine UTIs. Your veterinarian may recommend a urine culture before treatment, especially for recurrent infections.
What are the side effects of Clavamox?
Most common are vomiting, diarrhea, and decreased appetite. Rare but serious effects include allergic reactions (facial swelling, hives, difficulty breathing), which require emergency care.
Where can I buy Clavamox for my pet?
Clavamox is prescription-only. Smarty Vets dispenses Clavamox tablets, drops, and generic amoxicillin from a licensed veterinary pharmacy.
This article is for educational purposes and is not a substitute for veterinary advice. Always consult your veterinarian before starting, stopping, or changing any medication for your pet.