Cephalexin and amoxicillin-clavulanate are the two most commonly recommended first-choice antibiotics for dogs with bacterial skin infections. Both are effective against the staph bacteria responsible for the vast majority of these infections, and both have a low risk of serious side effects. But the “best” antibiotic for your dog depends on how deep the infection goes, whether resistant bacteria are involved, and whether a topical treatment might work just as well.
What Causes Most Canine Skin Infections
Nearly all bacterial skin infections in dogs, called pyoderma, are caused by a single type of staph bacteria: Staphylococcus pseudintermedius. In studies analyzing bacterial cultures from dogs with skin infections, Staphylococcus species showed up in roughly 96% of cases. This bacterium lives normally on your dog’s skin but causes problems when something disrupts the skin barrier, whether that’s allergies, a wound, moisture trapped in skin folds, or a weakened immune system.
Because one bacterial species dominates, vets can often predict which antibiotics will work without running lab tests first. That predictability is what makes first-line antibiotic choices reliable for straightforward infections. The complication is antibiotic resistance. Methicillin-resistant strains of this staph species (called MRSP) are increasingly common, with some studies estimating their prevalence at around 65% of resistant isolates globally. When resistance is suspected, lab testing becomes essential.
First-Choice Antibiotics
Veterinary guidelines from the International Society for Companion Animal Infectious Diseases (ISCAID) and the American Animal Hospital Association group canine skin antibiotics into tiers. The first-choice options all share two qualities: they reliably kill most non-resistant staph bacteria, and they carry a low risk of harm to your dog.
- Cephalexin. The most widely prescribed oral antibiotic for canine skin infections. It can be given once or twice daily, and studies show both dosing schedules resolve superficial infections equally well, typically within 14 to 42 days (median of about 28 days). The most common side effect is mild GI upset like vomiting or diarrhea, but it rarely requires stopping treatment.
- Amoxicillin-clavulanate. A broad-spectrum option given twice daily. The clavulanate component helps it overcome certain bacterial defense mechanisms that plain amoxicillin can’t handle. It’s a common alternative when cephalexin isn’t a good fit.
- Clindamycin. Given twice daily. It penetrates well into skin and bone tissue, making it useful for deeper infections in some cases.
All three are considered equally appropriate as a starting point for uncomplicated infections. Your vet will choose based on your dog’s size, any drug sensitivities, how easy it is to give pills, and cost. Plain amoxicillin (without clavulanate) is not effective against most staph skin infections in dogs.
When Topical Treatment Is Enough
For surface-level and superficial skin infections, current guidelines actually recommend topical therapy alone as the first step, not oral antibiotics. Chlorhexidine shampoos and sprays (typically at 4% concentration) have been shown to be as effective as systemic antibiotics for superficial pyoderma, clearing or substantially improving signs within about three weeks in most dogs. This holds true even for infections caused by resistant bacteria.
A typical regimen involves bathing with a medicated shampoo twice a week and applying a chlorhexidine spray daily to affected areas. If your dog tolerates this routine, it avoids the GI side effects that come with oral antibiotics and reduces the risk of breeding resistant bacteria. Even when your dog does need oral antibiotics, adding topical treatment speeds up healing and lowers the chance of resistance developing in the skin’s bacterial population.
Oral antibiotics are reserved for cases where topical therapy hasn’t worked, where the infection is too widespread for practical topical application, or where the infection has gone deep into the skin.
Superficial vs. Deep Infections
The depth of the infection changes the treatment approach significantly. Superficial pyoderma affects the outer layers of skin and hair follicles. You’ll typically see small pustules, crusts, circular patches of hair loss, or flaky red skin. These infections often respond to topical treatment alone, and when oral antibiotics are needed, a two-week initial course is standard, followed by a recheck to see if it’s working.
Deep pyoderma penetrates below the hair follicle into the deeper skin layers. It often looks more severe: swelling, draining wounds, pain, or firm nodules. Deep infections always require oral antibiotics, and the choice of drug should be based on a bacterial culture and sensitivity test rather than guesswork. The initial course runs at least three weeks, with a recheck before the prescription runs out to decide whether to continue. If signs are improving but haven’t fully resolved, treatment continues with reassessment every two weeks. Deep pyoderma can take many weeks to clear completely.
Second-Choice and Reserved Antibiotics
When first-line antibiotics don’t work, or when lab testing shows the bacteria are resistant, vets move to second-tier options. These include fluoroquinolones (like enrofloxacin and marbofloxacin), doxycycline, minocycline, and certain advanced-generation antibiotics. Guidelines are firm that these should only be used after culture and sensitivity testing confirms the bacteria are resistant to first-choice drugs.
Cefovecin is a long-acting injectable antibiotic that your vet gives as a single shot, maintaining effective drug levels for 7 to 14 days depending on the bacteria involved. In clinical trials, it cured about 82% of dogs with skin infections and improved another 10%, performing on par with daily oral antibiotics. It’s classified as a second-choice drug, meaning it’s not the default starting point, but it can be a practical option when giving oral medication at home is genuinely difficult.
For multidrug-resistant infections, a small group of reserved antibiotics exists, including rifampicin, amikacin, and chloramphenicol. These carry more serious potential side effects. Rifampicin can cause liver damage that is occasionally fatal in dogs, along with GI upset and orange discoloration of urine and tears. Chloramphenicol can suppress bone marrow function. These drugs are only considered when testing confirms no safer alternative will work.
How Your Vet Decides Which Antibiotic to Use
Diagnosis starts with a simple skin cytology test: your vet presses a glass slide or a piece of tape against the affected skin, stains the sample, and looks at it under a microscope. Finding bacteria inside white blood cells is a definitive sign of infection. This takes minutes, costs little, and tells your vet whether an antibiotic is truly needed.
For a first-time, uncomplicated superficial infection with staph bacteria on cytology, your vet can reasonably prescribe a first-line antibiotic without waiting for culture results. But a bacterial culture and sensitivity test becomes necessary in several situations: deep infections, rod-shaped bacteria on cytology (which have less predictable resistance patterns), infections that haven’t responded to a previous antibiotic course, infections in dogs with recent hospital stays or surgical wounds, and any case where antibiotic resistance is likely.
The culture identifies exactly which bacteria are present and tests them against a panel of antibiotics, giving your vet a clear map of what will and won’t work. This step takes a few days but prevents weeks of ineffective treatment.
Why Treating the Underlying Cause Matters
Antibiotics clear the bacterial infection, but pyoderma almost always has an underlying trigger. Allergies (environmental or food-related) are the most common. Hormonal conditions, parasites like mange mites, and immune system problems also predispose dogs to recurring skin infections. If that root cause isn’t identified and managed, the infection will likely come back once antibiotics stop, sometimes with bacteria that are harder to treat the second time around. Recurrent pyoderma is one of the clearest signals that something deeper is going on with your dog’s skin health or immune function.