By Dr. Michelle Frye, DVM · Published 2026-05-01
TL;DR. Cephalexin (Rilexine, Keflex) is a first-generation cephalosporin antibiotic that is the gold-standard first-line treatment for canine bacterial pyoderma. Dosed 22–30 mg/kg twice daily. Course is 21–30 days for superficial pyoderma, longer for deep. Finishing the entire course is non-negotiable.
The Pink Belly That Won't Quit
The dog comes in for itching. Under the belly fur, you find pink crusty bumps, the occasional pustule, a circular crust here and there with a darker center — the classic look of canine superficial pyoderma. The owner thinks it's mange. The Internet thinks it's ringworm. It's almost always staph. And cephalexin has been the answer for it for as long as I have been a veterinarian.
What Cephalexin Actually Does
Cephalexin is a first-generation cephalosporin antibiotic. Like amoxicillin, it disrupts bacterial cell-wall synthesis — but it is structurally tougher and has a different spectrum, hitting most strains of Staphylococcus pseudintermedius, the bacterium responsible for nearly all canine pyoderma.
- Dose: 22–30 mg/kg orally every 12 hours (some protocols use every 8 hours).
- Forms: capsules, tablets (including the chewable Rilexine), pharmacy-compounded liquid.
- Course length: 21–30 days for superficial pyoderma; 6–8 weeks for deep pyoderma.
- Continue until 7–14 days past visual resolution. The infection looks gone before it actually is.
Things People Are Wrong About
Myth 1: "Two weeks should do it." Two weeks is exactly how superficial pyoderma relapses. Twenty-one days minimum. Your veterinarian is not padding the course.
Myth 2: "If it's not better in 3 days, the antibiotic isn't working." Pyoderma improves slowly. The bumps stop multiplying first; the redness fades over a couple of weeks. Photos help — take one weekly and compare.
Myth 3: "Cephalexin is the same as Keflex." Yes, actually — same active ingredient. Veterinary brands (Rilexine) are FDA-approved for dogs and come in chewable tablets that pet most owners can administer.
Myth 4: "Recurrent pyoderma needs more antibiotic." Recurrent pyoderma needs an allergy plan. The bacteria are taking advantage of an inflamed skin barrier. Treat the underlying allergy and the bacteria stop coming back.
When NOT to Use Cephalexin
Avoid in dogs with a documented penicillin or cephalosporin allergy (cross-reactivity is real). Reduce the dose in significant kidney disease. For deep or recurrent pyoderma, a skin culture is increasingly important — methicillin-resistant Staphylococcus pseudintermedius (MRSP) is now common enough that empirical cephalexin sometimes fails. If your dog is on round 3 of cephalexin and still itchy, ask for a culture.
What I Tell Owners After 30 Years
Cephalexin is reliable, cheap, and effective for the right infection. It is not magic, and it is not a substitute for diagnosing the underlying skin disease. Give it with food, give it the full course, take photos along the way, and if your dog keeps having infections, the next conversation is about allergies — not another round of antibiotic.
Frequently Asked Questions
How long does cephalexin take to work in dogs?
Initial improvement is usually visible within 5–7 days, with continued resolution over 2–3 weeks. Always continue treatment for the full prescribed course.
How much cephalexin can I give my dog?
The usual dose is 22–30 mg/kg orally every 12 hours, prescribed and adjusted by your veterinarian based on your dog's weight and condition.
What is Rilexine?
Rilexine is the FDA-approved veterinary brand of cephalexin, formulated as a flavored chewable tablet for dogs. The active ingredient is identical to generic cephalexin.
Can cats take cephalexin?
Yes, though cephalexin is more commonly prescribed for dogs. Cats may receive it for skin infections and certain urinary infections, but other antibiotics are often selected based on the infection.
What are the side effects of cephalexin?
Vomiting, diarrhea, and decreased appetite are most common. Rare but serious side effects include allergic reactions (facial swelling, hives) and excitability.
Why does my vet prescribe cephalexin for 3 to 4 weeks?
Bacterial pyoderma resolves slowly and looks improved before the deeper infection clears. Treatment must continue 7–14 days past visible resolution to prevent relapse and resistance.
Can I give cephalexin with food?
Yes, and it is recommended — food significantly reduces GI side effects.
Where can I buy cephalexin for my dog?
Cephalexin is prescription-only. Smarty Vets dispenses Rilexine, generic cephalexin capsules and tablets, and compounded liquids from a licensed 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.