Article — Cephalexin Dosage for Dogs
Cephalexin dosage for dogs: complete vet-written guide
Cephalexin for dogs is dosed at 22 to 30 mg per kilogram of body weight every 12 hours, according to the Merck Veterinary Manual. Mild infections start at 10 to 15 mg/kg; severe deep pyoderma reaches 25 to 40 mg/kg every 8 to 12 hours. Cephalexin (brand names Rilexine and Keflex) is the most prescribed antibiotic in small-animal veterinary medicine and requires a vet prescription.
Cephalexin is the workhorse oral antibiotic for canine skin infections, urinary tract infections, soft-tissue infections, and post-surgical infection prophylaxis. It is a first-generation cephalosporin — a beta-lactam antibiotic that disrupts bacterial cell wall synthesis. Pharmacokinetic studies in dogs show peak plasma concentrations within 1 to 2 hours of an oral dose, with therapeutic levels maintained 8 to 12 hours.
What is cephalexin for dogs?
Cephalexin (chemical name: 7-(D-alpha-amino-alpha-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid) is a first-generation cephalosporin antibiotic. It binds penicillin-binding proteins in the bacterial cell wall and blocks the final cross-linking step in peptidoglycan synthesis. Bacteria with defective cell walls cannot withstand osmotic pressure and lyse.
The drug has broad activity against gram-positive bacteria (Staphylococcus pseudintermedius — the main cause of canine pyoderma — Streptococcus, and most enterococci) and some gram-negative bacteria (Proteus, Klebsiella, many E. coli strains). It is FDA-approved for canine use under the brand name Rilexine, a flavored chewable tablet released in 2009 by Virbac. Generic cephalexin capsules and the human-grade Keflex are also widely prescribed off-label for dogs.
Cephalexin is the most prescribed oral antibiotic in canine medicine according to the American Veterinary Medical Association. About 40 percent of all canine antibiotic prescriptions in the US use a cephalosporin, and cephalexin accounts for the largest share within that class.
Cephalexin dose by infection severity
The Merck Veterinary Manual and Plumb's Veterinary Drug Handbook list cephalexin dosing in three severity tiers. Mild infections include uncomplicated superficial skin lesions and routine UTIs. Moderate covers most pyoderma cases. Severe means deep pyoderma, complicated UTIs, or systemic soft-tissue infection.
Mild infection 10–15 mg/kg q12hModerate (most pyoderma) 15–25 mg/kg q12hSevere (deep pyoderma) 25–40 mg/kg q8–12hRenal impairment Reduce 25–50%For a 20 kg (44 lb) moderate-pyoderma case, this is 300 to 500 mg per dose, twice daily — closest to one and a half 250 mg capsules or four-fifths of a 500 mg capsule. A 5 kg toy breed needs 75 to 125 mg, best given as oral suspension (250 mg/5 mL = 50 mg/mL, so 1.5 to 2.5 mL per dose).
Cephalexin for canine pyoderma
Canine pyoderma — bacterial skin infection — is by far the most common indication for cephalexin in dogs. Three forms exist: surface pyoderma (hot spots, intertrigo), superficial pyoderma (impetigo, folliculitis), and deep pyoderma (furunculosis, cellulitis). Each requires a different treatment duration.
Surface pyoderma usually clears with topical therapy alone — chlorhexidine shampoo, mupirocin ointment — and rarely needs oral antibiotics. Superficial pyoderma typically needs 21 to 28 days of cephalexin, sometimes longer in dogs with concurrent allergic skin disease. Deep pyoderma is the toughest: 6 to 8 weeks of continuous cephalexin at the high dose (25 to 30 mg/kg twice daily), often combined with topical therapy and management of the underlying cause.
Cephalexin does not work against methicillin-resistant Staphylococcus pseudintermedius (MRSP), which now causes 15 to 30 percent of canine pyoderma in some referral populations. If a dog's pyoderma fails to improve after 14 days on cephalexin, request a bacterial culture and sensitivity panel before extending or escalating.
Cephalexin side effects in dogs
The most common cephalexin side effects in dogs are gastrointestinal: vomiting, diarrhea, and loss of appetite. These appear in 5 to 10 percent of treated dogs and usually resolve with food and continued dosing. Drooling and mild lethargy are less common.
Serious effects are rare. Allergic reactions occur in about 1 percent of dogs — facial swelling, hives, sudden vomiting, or labored breathing within 30 minutes of a dose. Anaphylaxis is exceedingly rare and requires immediate veterinary care. Dogs with a documented penicillin allergy carry a 1 to 3 percent cross-reactivity risk with cephalosporins. Long-term high-dose cephalexin can affect blood cell counts (transient neutropenia) and rarely causes hepatic enzyme elevation, both reversible on stopping the drug.
How to give cephalexin to a dog
Cephalexin can be given with or without food. Giving it with a small meal slows absorption slightly but reduces nausea, which is the most common side effect. The Rilexine flavored chewable is widely accepted on its own, often eaten like a treat. Generic capsules and tablets hide easily in soft cheese, peanut butter (xylitol-free only), or pill pockets.
For dogs that refuse pills, ask the prescribing vet about the oral suspension (250 mg/5 mL) — most dogs accept it mixed with a small amount of canned food. Skip the food trick on the first dose so you can confirm appetite and look for any allergic reaction.
Cephalexin vs. other dog antibiotics
Cephalexin is one of several first-line oral antibiotics in canine medicine. Amoxicillin-clavulanate (Clavamox) has broader gram-negative coverage and is preferred for bite wounds and mixed-flora infections. Doxycycline targets Mycoplasma, Bordetella, and tick-borne pathogens. Enrofloxacin (Baytril) is reserved for resistant gram-negative urinary infections, not first-line because of cartilage effects in growing dogs. Cephalexin's advantages are oral dosing twice daily, very low cost, and decades of safety data.
Cephalexin treatment length and resistance
Standard cephalexin courses run 7 to 14 days for uncomplicated skin and urinary infections. Superficial pyoderma typically needs 21 to 28 days, deep pyoderma 6 to 8 weeks. The cardinal rule is to continue treatment for 5 to 7 days beyond complete symptom resolution. Stopping early is the single most common cause of relapse and resistance.
Methicillin-resistant Staphylococcus pseudintermedius (MRSP) has emerged as a major concern in veterinary dermatology. Resistance rates climbed from under 5 percent in the early 2000s to 15 to 30 percent in some referral populations today. The drivers: under-dosing, premature treatment stop, and unnecessary antibiotic use. Culture-and-sensitivity testing before starting cephalexin for any recurrent or non-resolving infection is now standard of care.
Veterinary disclaimer
This cephalexin dosage calculator for dogs is for informational reference. Cephalexin is prescription-only in the United States, United Kingdom, European Union, Canada, Australia, and most other countries. Never give cephalexin to your dog without a current veterinary prescription based on a physical examination. Always complete the prescribed course, and contact the prescribing veterinarian immediately if your dog develops facial swelling, persistent vomiting, severe lethargy, or rash during treatment.
- Standard dose = 22–30 mg/kg every 12 hours (Merck Manual)
- Mild infection = 10–15 mg/kg q12h, 7–10 days
- Superficial pyoderma = 22 mg/kg q12h, 21–28 days
- Deep pyoderma = 30 mg/kg q12h, 6–8 weeks
- Renal disease = reduce dose 25–50%, vet supervised
- Forms = 250/500 mg caps, 250 mg/5 mL liquid, Rilexine 75/150/300/600 mg chewable
- Penicillin cross-reaction = 1–3% of allergic dogs
- Peak plasma = 1–2 hours after oral dose