Amoxicillin is one of the most commonly prescribed antibiotics for dogs, used to treat a wide range of bacterial infections including urinary tract infections, skin infections, respiratory infections, wound infections, and dental infections. It’s a penicillin-type antibiotic that kills bacteria by breaking down their cell walls, and veterinarians reach for it often because it works against many common bacterial strains while causing relatively few side effects.
Infections Amoxicillin Treats in Dogs
The FDA-approved uses of amoxicillin in dogs cover five broad categories of infection:
- Urinary tract infections (bladder infections, or cystitis)
- Respiratory tract infections (tonsillitis, bronchitis)
- Skin infections (bacterial dermatitis)
- Soft tissue infections (abscesses, lacerations, and infected wounds)
- Gastrointestinal infections (bacterial gastroenteritis)
Beyond these labeled uses, veterinarians also commonly prescribe amoxicillin for infected bite wounds and dental infections. It’s particularly useful against anaerobic bacteria, the kind that thrive in low-oxygen environments like deep wounds and abscesses. Bladder infections are one of the most frequent reasons your vet will choose plain amoxicillin, because the kidneys concentrate so much of the drug into urine that even bacteria that might resist it elsewhere in the body are often overwhelmed in the urinary tract.
How Amoxicillin Kills Bacteria
Amoxicillin belongs to the beta-lactam family of antibiotics. It works by binding to proteins that bacteria need to build and maintain their cell walls. Once those proteins are blocked, the bacteria can’t hold themselves together. The drug also triggers self-destruct enzymes already present inside bacterial cells, causing the cell wall to break apart. This makes amoxicillin bactericidal, meaning it actively kills bacteria rather than just slowing their growth.
Plain Amoxicillin vs. Amoxicillin-Clavulanate
You’ll sometimes see your vet prescribe amoxicillin-clavulanate (sold under brand names like Clavamox) instead of plain amoxicillin. The difference matters. Some bacteria produce an enzyme that destroys amoxicillin before it can work. Clavulanic acid is added to block that enzyme, essentially shielding the antibiotic so it can do its job. This combination is considered a broader-spectrum option and is typically the first choice for bite wounds and skin infections where the specific bacteria haven’t been identified yet.
Plain amoxicillin works well when the bacteria involved don’t produce that protective enzyme, which is the case for many streptococcal infections, Pasteurella (common in bite wounds), and most bladder infections. The tradeoff with the combination drug is a higher rate of gastrointestinal side effects. In one comparative study, the amoxicillin-clavulanate group experienced side effects at roughly 17.5% compared to 10.3% for plain amoxicillin. So when your vet knows the infection will respond to plain amoxicillin alone, there’s good reason to use it.
What Amoxicillin Doesn’t Work Against
Amoxicillin has a significant blind spot: bacteria that produce the enzyme (called penicillinase) that breaks it down. Most staphylococcal infections fall into this category, which is why skin infections caused by Staph are typically treated with the amoxicillin-clavulanate combination instead. The exceptions are Staph bladder infections, where drug concentrations in urine are high enough to overcome the resistance.
Certain bacteria are inherently resistant to amoxicillin regardless of the formulation. All Pseudomonas strains and most Klebsiella and Enterobacter species won’t respond to it. Resistance is also a growing concern with E. coli, one of the most common causes of urinary and gut infections in dogs. Regional data shows that up to 50% of E. coli strains are now resistant to amoxicillin, and roughly 40% resist even the amoxicillin-clavulanate combination. This is why your vet may want to run a culture and sensitivity test before prescribing, particularly for recurring infections.
MRSA and its veterinary counterpart MRSP (methicillin-resistant Staphylococcus pseudintermedius) are completely resistant to amoxicillin and all related antibiotics. These infections require different drug classes entirely.
Common Side Effects
Most dogs tolerate amoxicillin well. The most common side effects are gastrointestinal: decreased appetite, vomiting, and diarrhea. These are usually mild and resolve on their own. Giving the medication with food can help reduce stomach upset.
Serious allergic reactions are rare but possible. Signs include facial swelling, skin rash, fever, or difficulty breathing. If your dog shows any of these symptoms, stop giving the medication and contact your vet immediately. Dogs with a known allergy to penicillin-type antibiotics should not take amoxicillin.
What to Expect During Treatment
Amoxicillin is given orally, typically every 8 to 12 hours. The standard dose range is 11 to 15 mg per kilogram of body weight, though your vet will determine the exact amount based on your dog’s size and the type of infection. It comes in tablet and liquid forms, and most dogs take it without much fuss, especially when it’s wrapped in food or a treat.
Treatment length varies depending on the infection. Simple urinary tract infections may require 5 to 7 days of treatment. Skin infections and deeper soft tissue infections often need longer courses, sometimes several weeks. One of the most important things you can do is finish the entire prescribed course, even if your dog seems better after a few days. Stopping early is one of the main drivers of antibiotic resistance, and it raises the risk that the infection comes back stronger.
Your vet may schedule a follow-up visit or recheck culture to confirm the infection has fully cleared, particularly for urinary tract infections or any infection that’s been slow to improve.