Cephalexin for Dogs Dosage Calculator
Enter your dog's weight, choose the prescribed dose rate and frequency, then pick the tablet or liquid formulation you have on hand. The calculator shows the milligrams per dose, the daily total, and exactly how many tablets or millilitres to give at each administration. Switch between metric and imperial units instantly. Always confirm the dose with your veterinarian before starting treatment.
What is cephalexin and what does it treat in dogs?
Cephalexin is a first-generation cephalosporin antibiotic that works by disrupting the cell wall synthesis of bacteria, causing them to rupture and die. It is bactericidal and effective against a wide range of gram-positive and some gram-negative organisms. In dogs, veterinarians prescribe it for skin and soft-tissue infections (pyoderma, hot spots, wound infections), urinary tract infections (UTIs), bone infections (osteomyelitis), respiratory tract infections, and mastitis. It is available under brand names such as Keflex, Rilexine, and Vetri-Keflex, and comes in 250 mg and 500 mg capsules, 75-600 mg chewable tablets, and oral suspensions of 25-50 mg/mL.
How is the cephalexin dose for dogs calculated?
The dose is always calculated from your dog's weight in kilograms. The MSD (Merck) Veterinary Manual lists cephalexin at 15-45 mg per kilogram per dose, given every 6 to 12 hours, and the FDA-approved label for Rilexine chewable tablets specifies 22 mg/kg (10 mg/lb) twice daily for 28 days for secondary superficial bacterial pyoderma. Your vet selects the dose rate and how often to give it based on the type and severity of the infection. To find the dose, multiply the weight in kg by the dose rate: for example, a 25 kg dog at 22 mg/kg needs 550 mg per dose. If the dog weighs 55 lb, convert first (55 x 0.4536 = 24.9 kg) then multiply. Twice-daily dosing (every 12 hours) is the most common schedule for skin infections, while more serious infections may call for three or four times a day. Note that the rate is per dose, not per day: a dog on 22 mg/kg twice daily receives 44 mg/kg over 24 hours.
How long does a cephalexin course last for dogs?
Treatment duration depends on the type and severity of infection. Urinary tract infections generally require 7-14 days, surface skin infections 14-21 days, and deep pyoderma or recurrent skin infections 21-28 days or longer. Bone infections (osteomyelitis) often need 6-8 weeks or more. Chronic skin conditions such as recurrent deep pyoderma can need maintenance therapy for several months. Never stop a course early because your dog appears better; stopping too soon can leave residual bacteria, select resistant strains, and cause the infection to relapse. If your dog has not improved within 48-72 hours of starting treatment, contact your vet.
Side effects, safety, and when to call your vet
The most common side effects are gastrointestinal: vomiting, diarrhea, drooling, and reduced appetite. Giving cephalexin with food or a small treat reduces stomach upset significantly. Rarer but more serious reactions include allergic hypersensitivity (facial swelling, hives, difficulty breathing, collapse), which requires immediate veterinary attention. Dogs with known penicillin allergy may also react to cephalexin due to cross-reactivity between beta-lactam classes. Cephalexin should be used cautiously in dogs with kidney disease, as the kidneys clear most of the drug; dose reduction or increased intervals may be needed. Prolonged courses can sometimes promote secondary yeast infections. Store capsules and tablets at room temperature; reconstituted liquid suspensions must be refrigerated and discarded after 14 days.
Cephalexin dosage guide by dog weight
| Weight (lb) | Weight (kg) | Dose per admin (mg) | Daily total (mg) | Convenient formulation |
|---|---|---|---|---|
| 5 | 2.3 | 50 | 100 | Oral suspension 25 mg/mL (2 mL) |
| 10 | 4.5 | 100 | 200 | Oral suspension 25 mg/mL (4 mL) |
| 15 | 6.8 | 150 | 299 | 150 mg chewable (1) |
| 20 | 9.1 | 200 | 399 | Oral suspension 50 mg/mL (4 mL) |
| 30 | 13.6 | 299 | 599 | 300 mg chewable (1) |
| 40 | 18.1 | 399 | 798 | Oral suspension 50 mg/mL (8 mL) |
| 50 | 22.7 | 499 | 998 | Oral suspension 50 mg/mL (10 mL) |
| 60 | 27.2 | 599 | 1197 | 600 mg chewable (1) |
| 75 | 34 | 748 | 1497 | 600 mg chewable (1) + 150 mg (1) |
| 100 | 45.4 | 998 | 1996 | Oral suspension 50 mg/mL (20 mL) |
Estimates at the FDA-approved Rilexine rate of 22 mg/kg (10 mg/lb) per dose, given twice daily (q12h). Actual dose set by your vet.
Frequently asked questions
What is the standard cephalexin dose for dogs?
The MSD Veterinary Manual lists 15-45 mg per kilogram of body weight per dose, given every 6-12 hours. For superficial bacterial pyoderma the FDA-approved Rilexine label specifies 22 mg/kg (10 mg/lb) twice daily for 28 days, which is the most common starting point. Your veterinarian determines the exact dose and schedule based on the infection type, its severity, your dog's kidney function, and other medications your dog takes.
Can I give my dog the same cephalexin prescribed for humans?
Human cephalexin (Keflex) contains the same active ingredient as veterinary formulations, but you must never give your dog any medication without explicit veterinary instruction. Dosing for dogs differs, the capsule formulations available in human pharmacies may not match the dose your dog needs, and other ingredients in some human products may be harmful. Always get a prescription from your vet.
What if I miss a dose?
Give the missed dose as soon as you remember. If it is nearly time for the next scheduled dose, skip the missed one and continue as normal. Never double up by giving two doses at once. To avoid forgetting doses, set phone reminders that match the prescribed schedule.
How do I convert my dog's weight from pounds to kilograms?
Divide the weight in pounds by 2.205, or multiply by 0.4536. For example, a 50 lb dog weighs 50 x 0.4536 = 22.7 kg. This calculator does the conversion automatically when you select imperial units.
How long does it take for cephalexin to work in dogs?
Most dogs show measurable improvement within 24-72 hours of starting treatment as bacterial load begins to fall. Visible improvement of skin lesions typically takes 5-7 days. If there is no improvement after 72 hours or the dog worsens at any point, contact your veterinarian: the infection may be caused by a resistant organism or require a different antibiotic.
Does cephalexin need to be given with food?
Cephalexin can be given with or without food, but giving it with a meal or a small food treat significantly reduces the chance of nausea and vomiting. If your dog vomits after a dose given on an empty stomach, try giving the next dose alongside food.
Is cephalexin safe for puppies and pregnant or nursing dogs?
Cephalexin is generally considered safe for puppies and has a good safety record in pregnant and lactating dogs, but it does cross the placenta and is excreted in milk. The veterinarian weighs the benefit of treating the infection against any potential risk to offspring. Always disclose if your dog is pregnant, nursing, or under six months old before a prescription is written.
Sources
- Plumb D.C. Cephalexin. In: Plumb's Veterinary Drug Handbook, 10th ed. PharmaVet Inc., 2023.
- FDA/DailyMed - RILEXINE (cephalexin tablets) Chewable Tablets for Dogs, NADA 141-326: 22 mg/kg (10 mg/lb) twice daily for 28 days.
- MSD (Merck) Veterinary Manual - Dosages of Cephalosporins: cephalexin 15-45 mg/kg PO q6-12h in dogs.