Cephalexin 500 mg is one of the most commonly prescribed antibiotics for dogs, used primarily to treat bacterial skin infections, urinary tract infections, and wound infections. It belongs to the first-generation cephalosporin class, which works by disrupting bacterial cell walls, causing the bacteria to die. The 500 mg tablet size is typically appropriate for medium to large dogs weighing roughly 25 to 75 pounds, though the exact dose depends on the condition being treated and your dog’s specific weight.
Skin Infections Are the Most Common Use
The number one reason veterinarians reach for cephalexin is bacterial pyoderma, which is the clinical term for a bacterial skin infection. These infections are almost always caused by a type of staph bacteria called Staphylococcus pseudintermedius that naturally lives on your dog’s skin but can overgrow and cause problems. Cephalexin is considered a “first tier” antibiotic for treating pyoderma, meaning it’s one of the go-to choices before trying anything stronger.
Skin infections in dogs come in three levels of severity. Surface-level infections include hot spots and irritation in skin folds. Superficial infections go a bit deeper, invading the hair follicle and causing conditions like folliculitis or impetigo, which you’ll notice as small bumps, pustules, or patchy hair loss. Deep infections, called furunculosis, break through into the lower layers of skin and tend to be more painful and harder to clear. Cephalexin can be prescribed for all three types, though deeper infections require longer treatment courses.
Urinary Tract and Other Infections
Cephalexin is also effective for simple urinary tract infections in dogs. Clinical studies comparing it against other common antibiotics for bladder infections in female dogs found no difference in cure rates, making it a reliable option. It works well against many of the gram-positive bacteria that cause UTIs, though it’s less effective against certain gram-negative bacteria and doesn’t work at all against enterococcus species.
Beyond skin and bladder infections, veterinarians may prescribe cephalexin for wound infections, abscesses, bone infections, and respiratory tract infections. Its broad usefulness and relatively mild side effect profile make it a versatile choice across many common bacterial conditions.
Dosing and the 500 mg Tablet
The standard veterinary dose for cephalexin ranges from 15 to 45 mg per kilogram of body weight, given every 6 to 12 hours depending on the infection. At the middle of that range (around 30 mg/kg twice daily, which is a common dosing protocol for skin infections), a 500 mg tablet fits a dog weighing about 35 to 40 pounds. Larger dogs may need two tablets per dose, while smaller dogs might get a lower-strength capsule or a liquid formulation.
Your vet will choose the specific dose and frequency based on the type and severity of infection. More aggressive infections often call for higher doses given more frequently, while straightforward cases may only need twice-daily dosing.
How Long Treatment Typically Lasts
For most skin infections, expect a treatment course of 2 to 3 weeks, or about 7 days beyond the point where the infection looks fully healed on the surface. This is a critical detail: stopping the medication as soon as your dog’s skin looks better is one of the most common mistakes owners make. Bacteria can still be present beneath the surface even when visible symptoms have cleared.
For deeper or more severe pyoderma, treatment can extend well beyond three weeks. The general veterinary guideline is to continue antibiotics for 7 to 21 days after surface healing, depending on severity. Urinary tract infections typically require a shorter course, often around 10 days. Finishing the full prescription helps prevent the infection from returning and reduces the risk of antibiotic resistance.
Side Effects to Watch For
Cephalexin is well tolerated by most dogs. The most common side effect is mild nausea or stomach upset, which you might notice as your dog being less interested in food or occasionally vomiting after a dose. Giving the medication with a small amount of food or a treat usually solves this.
Less commonly, some dogs develop hyperexcitability or excessive drooling while taking cephalexin. If you notice either of these, let your vet know, as switching to a different antibiotic is straightforward. Allergic reactions are possible but rare. Dogs with known allergies to penicillin-type antibiotics have a slightly higher chance of reacting to cephalexin, since the two drug classes share a similar chemical structure.
Dogs That Need Extra Monitoring
Dogs with kidney problems are at higher risk of side effects from cephalexin because the drug is cleared through the kidneys. If your dog has known kidney disease, your vet may adjust the dose or choose a different antibiotic altogether. While cephalexin has no major known drug interactions in dogs, it can potentially interact with blood-thinning medications, so mention any other medications your dog takes when the prescription is written.
Giving Cephalexin at Home
Cephalexin can be given with or without food. If your dog gets an upset stomach on an empty stomach, pairing the dose with a small meal or treat is perfectly fine and won’t reduce the drug’s effectiveness. The capsules and tablets should be stored at room temperature. Try to space doses as evenly as possible throughout the day. If your dog is on a twice-daily schedule, aim for roughly 12 hours apart. If you miss a dose, give it as soon as you remember, then resume the regular schedule rather than doubling up.