How this instrument works
Cephalexin is a first-generation cephalosporin antibiotic used in dogs mainly for skin and soft-tissue infections, including bacterial pyoderma. This page deliberately shows two different figures rather than blending them: Merck's Veterinary Manual lists a broad general dosing range for cephalosporins in dogs of 15–45 mg/kg, while the FDA-approved product Rilexine carries its own specific label dose of 22 mg/kg, twice daily, for a defined 28-day course treating pyoderma.
Those two numbers answer different questions. The general range reflects how cephalexin gets dosed across various infections and formulations in veterinary practice; the Rilexine label dose is the exact, FDA-reviewed figure for one approved product and one approved indication. A veterinarian choosing an antibiotic dose is working from the specific product and diagnosis in front of them, not just a generic range — which is exactly why this isn't a plug-and-treat calculation.
This tool provides a reference range based on published veterinary sources. It is not a substitute for professional veterinary advice. Always consult your veterinarian before giving any medication, and contact your vet or an animal poison control hotline — for example the ASPCA Animal Poison Control Center, (888) 426-4435 — immediately if you suspect a toxic ingestion. Antibiotic dosing also depends on kidney function, the specific infection being treated, and completing the full prescribed course — stopping early, even once symptoms improve, can contribute to antibiotic resistance.
- Weigh your dog on a reliable scale, or use a recent veterinary weight, in kilograms.
- Read the general range: the low and high milligram figures from Merck's 15–45 mg/kg band.
- Read the FDA label dose separately: the milligram figure from the specific 22 mg/kg Rilexine dose.
- Do not average or blend the two numbers — they answer different questions, as explained above.
- Confirm the actual prescribed dose, product, and course length with your veterinarian before giving anything.
Worked example — a 20 kg dog
A 20 kg dog: the general range is 20 × 15 = 300 mg to 20 × 45 = 900 mg, a wide band reflecting cephalexin's use across different infections and dosing schedules. The FDA-approved Rilexine label dose, by contrast, is one specific figure: 20 × 22 = 440 mg, given twice daily for a 28-day course, for pyoderma specifically.
Smaller and larger dogs scale the same way: a 10 kg dog spans a 150–450 mg general range with a 220 mg Rilexine label dose, while a 34 kg large dog spans 510–1530 mg generally with a 748 mg Rilexine label dose. The gap between the general range and the specific label dose stays proportional at every weight.
Questions
Why does this page show two different cephalexin doses?
Because they answer different questions. Merck's 15–45 mg/kg is a general reference range covering cephalexin's varied veterinary uses; the 22 mg/kg figure is the exact FDA-approved label dose for one specific product, Rilexine, treating one specific condition, pyoderma. This tool provides a reference range based on published veterinary sources — it is not a substitute for professional veterinary advice on which figure applies to your dog's diagnosis.
Is cephalexin approved for use in dogs?
Yes — Rilexine (cephalexin chewable tablets) carries FDA approval specifically for treating secondary superficial bacterial pyoderma in dogs, per its DailyMed label. Other cephalexin dosing for other infections in dogs may still occur under a veterinarian's clinical judgment even without a matching FDA-approved indication.
Can I stop the antibiotic once my dog's skin looks better?
No, not without checking with your veterinarian first. The Rilexine label specifies a full 28-day course for pyoderma; stopping early, even when symptoms improve, risks incomplete treatment and can contribute to antibiotic resistance. Always consult your veterinarian before changing a prescribed antibiotic course.
What if my dog has a penicillin or cephalosporin allergy?
Cephalexin is contraindicated in dogs with a known allergy to cephalexin or to any penicillin or cephalosporin-class antibiotic, per the Rilexine label. Tell your veterinarian about any prior drug reactions before starting treatment, and contact them immediately if you see facial swelling, hives, or difficulty breathing after a dose.
Does this dose apply to cats too?
No — use the separate cat cephalexin calculator on this site instead. Cats have their own dosing range and, importantly, no FDA-approved cephalexin product exists for cats, unlike dogs, which have Rilexine. Mixing up the two species' figures is exactly the kind of error a veterinarian should catch before you give anything.
References
- Merck Veterinary Manual — Table: Dosages of Cephalosporins
- FDA/DailyMed — Rilexine (cephalexin) Chewable Tablets label
- Merck Veterinary Manual — Cephalosporins and Cephamycins Use in Animals
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.