What Is Cephalexin and What Does It Treat?
Cephalexin is a widely used antibiotic in dogs, particularly for skin infections. It is a first-generation cephalosporin — a close relative of the penicillins — and is known by human brand names such as Keflex and the veterinary brand Rilexine.
Cephalexin works by disrupting the bacterial cell wall. Bacteria need an intact cell wall to survive; cephalexin blocks the enzymes that build it, so the bacteria break down and die. It is a bactericidal antibiotic effective against many of the bacteria that cause common canine infections — especially the _Staphylococcus_ species that are the usual culprits in skin disease.
Veterinarians most commonly prescribe cephalexin for:
- Skin infections (pyoderma) — its single most common use; cephalexin is a long-standing first-choice treatment
- Wounds, abscesses and soft-tissue infections
- Urinary tract infections
- Other infections caused by susceptible bacteria
Cephalexin is a long-established, well-understood, generally well-tolerated antibiotic, and it remains a mainstay of canine skin-infection treatment.
Cephalexin is a prescription medicine. Use the calculator above to understand the typical dose, but a veterinarian should confirm the diagnosis and set the prescription. For more, see PuppaDogs’ guides to cephalexin for dogs and the chewable veterinary brand Rilexine.
How the Cephalexin Dosage Calculator Works
The calculator estimates a dose from your dog’s body weight and a chosen dose level. It then:
- Shows the dose per administration in milligrams.
- Converts it into a number of capsules or tablets in the strength you select.
- Lets you choose twice- or three-times-daily dosing.
- Flags penicillin/cephalosporin allergy and other cautions.
Enter your dog’s weight, choose the reason for use, dose level, frequency and the strength you have, tick any health considerations, then press Calculate Dose.
How Cephalexin Doses Are Calculated for Dogs
The Standard Dose Range
The commonly used oral cephalexin dose for dogs is approximately:
22–30 mg/kg of body weight, every 8 to 12 hours.
For skin infections (pyoderma) in particular, veterinarians often use the upper part of this range — around 30 mg/kg — because reaching effective drug levels in the skin is important for a successful outcome. Your veterinarian sets the exact dose and frequency.
Forms and Strengths
- Capsules and tablets: commonly 250 mg and 500 mg (human-generic and Keflex).
- Rilexine — the veterinary brand — comes as flavoured chewable tablets in 75, 150, 300 and 600 mg strengths.
- Oral suspension is also available, which is useful for small dogs.
Cephalexin Dosage Chart for Dogs
This chart shows the standard dose (22 mg/kg). It is a reference only — your veterinarian’s prescription takes priority.
| Dog weight | Dose per administration | Frequency |
|---|---|---|
| 5 kg (11 lb) | ~110 mg | every 8–12 h |
| 10 kg (22 lb) | ~220 mg | every 8–12 h |
| 20 kg (44 lb) | ~440 mg | every 8–12 h |
| 30 kg (66 lb) | ~660 mg | every 8–12 h |
| 40 kg (88 lb) | ~880 mg | every 8–12 h |
How to Give Cephalexin to Your Dog
- As directed — every 8 or 12 hours, at consistent times.
- Give with food. This is genuinely helpful — it reduces the chance of stomach upset, which is the most common side effect.
- Hide capsules in a small treat, or use the flavoured Rilexine chewables if your dog accepts them.
- Finish the entire course, even if the infection looks healed.
- Missed dose: give it as soon as you remember, then continue on schedule; if it is nearly time for the next dose, skip the missed one — never double up.
Side Effects and Safety Warnings
Cephalexin is generally well tolerated. The most common side effects are mild and digestive:
- Reduced appetite
- Vomiting or loose stool
- Drooling shortly after a dose — cephalexin can taste bitter, and this is harmless
Giving the medication with food noticeably reduces stomach upset.
Allergy Is the Key Concern
Because cephalexin is a cephalosporin — closely related to the penicillins — the most important safety issue is allergy. A dog with a known allergy to penicillins or cephalosporins should not receive cephalexin, as there is potential for cross-reactivity. Tell your veterinarian about any previous reaction.
Stop the medication and contact your veterinarian promptly if you see signs of an allergic reaction — facial swelling, hives, intense itching or difficulty breathing — or severe or bloody diarrhoea.
When to Use Caution
- Penicillin or cephalosporin allergy — avoid cephalexin.
- Kidney disease — the drug is cleared mainly by the kidneys; the dose or interval may need adjusting.
- Pregnant or nursing dogs — generally considered usable, but only on veterinary advice.
Skin Infections Need a Long Course
This is the most important practical point with cephalexin. Canine skin infections (pyoderma) are slow to clear, and they need a longer course of antibiotics than owners often expect — frequently 3–4 weeks or more, and usually continued for a week or two beyond the point at which the skin looks completely normal.
Stopping cephalexin as soon as the skin appears healed is a leading cause of recurrent skin infections that become progressively harder to treat. Give the full course your veterinarian prescribes — even when your dog looks better — and attend any recommended recheck so the vet can confirm the infection has truly resolved.
Conclusion
Cephalexin is a long-established, effective, broadly used antibiotic for canine skin and other bacterial infections, dosed at roughly 22–30 mg/kg every 8–12 hours. The calculator above gives you that estimate and converts it into capsules or tablets. Give it with food, watch for allergy in penicillin-sensitive dogs — and, above all, complete the full course, which for skin infections is often longer than expected. The diagnosis, dose and course length should always be guided by your veterinarian.
Frequently Asked Questions
How much cephalexin do I give my dog?
The commonly used oral cephalexin dose for dogs is about 22-30 mg/kg of body weight, every 8 to 12 hours. For skin infections, vets often use the upper part of that range, around 30 mg/kg. As a guide that is roughly 220 mg per dose for a 10 kg dog. Your veterinarian sets the exact dose and course length.
What is cephalexin used for in dogs?
Cephalexin is a first-generation cephalosporin antibiotic. Its most common use in dogs is treating skin infections (pyoderma), and it is also used for wounds, abscesses, soft-tissue infections and urinary tract infections caused by susceptible bacteria. It is a long-standing mainstay of canine skin-infection treatment.
How long does my dog need to take cephalexin?
It depends on the infection. Skin infections in particular are slow to clear and often need a long course – commonly 3-4 weeks or more, usually continued for a week or two beyond the point the skin looks normal. Stopping early is a leading cause of recurrent skin infections. Always finish the full course your vet prescribes.
Should cephalexin be given with food?
Yes, giving cephalexin with food is recommended. Food noticeably reduces the chance of stomach upset, which is the most common side effect. The flavoured Rilexine chewable form is also designed to be easy to give. Some dogs drool briefly after a dose because cephalexin tastes bitter – this is harmless.
What are the side effects of cephalexin in dogs?
Cephalexin is generally well tolerated. The most common side effects are mild digestive ones – reduced appetite, vomiting or loose stool – and brief drooling after a dose. Giving it with food helps. The main serious concern is an allergic reaction; contact your vet for facial swelling, hives, difficulty breathing or severe diarrhoea.
Can a dog with a penicillin allergy take cephalexin?
Cephalexin is a cephalosporin, closely related to penicillins, and there can be cross-reactivity between the two classes. A dog with a known allergy to penicillins or cephalosporins should generally not receive cephalexin. Always tell your veterinarian about any previous antibiotic reaction so a different class can be chosen.
Related PuppaDogs Calculators
Continue building your dog’s personalised care plan with these related PuppaDogs calculators:
- Dog Pregnancy / Whelping Due-Date Calculator
- Puppy Weight Predictor (Adult Weight Calculator)
- Heatstroke Risk Calculator for Dogs
- Bloat (GDV) Risk Calculator for Dogs
- Dog Life Expectancy Calculator (Breed, Body Condition, Lifestyle)
- Spay/Neuter Timing Calculator for Dogs (Breed-Specific)
References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Rilexine (cephalexin) – veterinary label and dosing information; Keflex (cephalexin) prescribing information.
- Plumb DC. Plumb’s Veterinary Drug Handbook. 10th ed. Hoboken, NJ: Wiley-Blackwell, 2023 – cephalexin (cefalexin) monograph.
- Merck Veterinary Manual. Cephalosporins; pyoderma and bacterial skin disease in dogs. merckvetmanual.com.
- International Society for Companion Animal Infectious Diseases (ISCAID). Antimicrobial use guidelines for canine superficial bacterial folliculitis (pyoderma).
- PuppaDogs. Cephalexin for Dogs: Benefits, Dosage, Side Effects, and More. puppadogs.com.
