Article — Cephalexin Dosage for Cats
Cephalexin dosage for cats: a vet-checked guide
Cephalexin for cats is dosed at 22 to 30 mg per kilogram of body weight every 12 hours. The Merck Veterinary Manual lists this range for skin and soft-tissue infections, with the upper end reaching 35 mg/kg for deep pyoderma. Cephalexin is prescription-only and is used off-label in feline medicine — always start with a veterinary exam.
Cephalexin, sold under the brand names Keflex and Rilexine, is a first-generation cephalosporin antibiotic that disrupts bacterial cell wall synthesis. In cats, it covers most of the gram-positive bacteria responsible for skin and urinary infections, including Staphylococcus pseudintermedius, Streptococcus species, and many strains of E. coli. Pharmacokinetic studies show oral cephalexin reaches peak plasma in 1.8 hours and maintains therapeutic concentrations for 8 to 12 hours, which is why the standard schedule is twice daily.
What is cephalexin for cats?
Cephalexin is a beta-lactam antibiotic, structurally related to penicillin. It works by binding penicillin-binding proteins in the bacterial cell wall, blocking the cross-linking step that gives the wall its strength. Bacteria with weakened walls lyse under osmotic pressure. The drug is bactericidal — it kills bacteria rather than just slowing them.
Despite widespread veterinary use, cephalexin has no FDA approval for cats. Veterinarians prescribe it off-label, a legal and common practice when a drug developed for humans or another species addresses a known feline indication. The most common feline uses are superficial pyoderma, abscesses, cat bite wounds, urinary tract infections, and post-surgical infection prevention.
Cephalexin was discovered in 1967 by Eli Lilly chemists and entered the US market as Keflex in 1971. The FDA approved Rilexine flavored chewable tablets specifically for canine pyoderma in 2009 — but no feline-labeled product has ever been approved, despite decades of safe off-label use in cats.
Cephalexin dose by infection type
The Merck Veterinary Manual stratifies cephalexin dosing by infection location. Skin and soft-tissue infections need higher concentrations because the antibiotic must penetrate dermal tissue; urinary tract infections need less because cephalexin is excreted through the kidneys and concentrates in urine.
Skin / soft tissue 22–35 mg/kg q12hUrinary tract 12–25 mg/kg q12hOther susceptible 10–15 mg/kg q6–8hSenior / renal Reduce by 20–30%A 4.5 kg (10 lb) domestic shorthair with a skin infection therefore needs 99 to 158 mg per dose, given every 12 hours. The closest practical formulation is the 125 mg/5 mL pediatric oral suspension (25 mg/mL), measured at 4 to 6 mL per dose with an oral syringe.
How to give cephalexin to a cat
Liquid suspension is the easiest form for cats under 5 kg, because dose adjustment is continuous rather than constrained to half or quarter tablets. Compounding pharmacies can prepare cephalexin in tuna, chicken, or fish flavor for cats who refuse the standard formulation.
For tablets and capsules, the standard human-pharmacy strengths are 250 mg and 500 mg — both are too large for most cats and need splitting. Pill splitters give cleaner halves than a kitchen knife, and pill pockets (Greenies, Pill Pockets, or homemade tuna paste) cover the bitter taste. Always follow each dose with a few millilitres of water to prevent capsule lodging in the esophagus, which is a real cause of feline esophagitis.
Cats have narrow esophagi and weak peristaltic clearance. Dry-swallowed tablets can lodge against the lower esophageal sphincter and cause chemical burns over hours. After every pill dose, give 3 to 5 mL of water or a small wet-food treat to flush the pill into the stomach.
Cephalexin side effects in cats
The most common feline side effects of cephalexin are gastrointestinal: vomiting, diarrhea, and reduced appetite. These appear in 5 to 15 percent of cats and usually resolve within 48 hours of starting the drug or with a switch to giving it with food. Less common effects include drooling (a sign of bitter taste, not toxicity), mild lethargy, and skin rash.
Allergic reactions are rare but real. Facial swelling, hives, or sudden vomiting within 30 minutes of a dose require immediate veterinary care. Cats with a documented penicillin allergy have a 1 to 3 percent cross-reactivity risk with cephalosporins, including cephalexin. In the very rare case of anaphylaxis, the first-line treatment is intravenous fluids, epinephrine, and antihistamine.
Cephalexin and feline kidney disease
Cephalexin is renally cleared. About 80 percent of an oral dose appears unchanged in urine within 8 hours. In cats with chronic kidney disease (CKD), reduced glomerular filtration prolongs the drug's half-life and raises plasma levels with repeated doses. The standard adjustment for IRIS Stage 2 or higher CKD is a 20 to 30 percent dose reduction or a longer interval between doses, set by the supervising veterinarian based on the cat's creatinine and SDMA values.
Senior cats (over 12 years old) should have baseline kidney bloodwork before starting any antibiotic course longer than 7 days. Subclinical CKD is present in 30 to 40 percent of cats over 12 and only becomes apparent through laboratory testing.
Cephalexin treatment length
Standard treatment courses run 7 to 14 days for simple skin infections and uncomplicated urinary tract infections. Deep pyoderma — the kind that involves hair follicles and deeper dermis — needs 3 to 8 weeks of continuous therapy. The cardinal rule is to continue dosing for 5 to 7 days beyond complete symptom resolution. Stopping early is the single most common cause of relapse and antibiotic resistance.
Set phone alarms for cephalexin dose times during the entire course. Missed or delayed doses drop plasma concentration below the minimum inhibitory concentration (MIC) and let surviving bacteria multiply, raising the risk of resistant regrowth. Aim for 12 hour intervals within ±2 hours.
Cephalexin vs. other feline antibiotics
Cephalexin is one of several first-line antibiotics in feline medicine. Amoxicillin-clavulanate (Clavamox) has a broader spectrum and slightly better gram-negative coverage. Doxycycline is preferred for upper respiratory infections caused by Mycoplasma or Chlamydophila. Convenia (cefovecin) is a long-acting injectable cephalosporin that lasts 14 days from a single dose — useful when oral medication is impossible. Cephalexin's advantages are oral administration, low cost, and a long safety record specifically in cats.
Veterinary disclaimer
This cephalexin dosage calculator for cats is a reference tool. Cephalexin is prescription-only in the United States, United Kingdom, European Union, Canada, and Australia. Never administer cephalexin to your cat without a current veterinary prescription based on a physical exam. Always finish the prescribed course even after symptoms resolve, and contact the prescribing veterinarian immediately if your cat shows facial swelling, persistent vomiting, lethargy, or loss of appetite during treatment.
- Standard cat dose = 22–30 mg/kg every 12 hours (Merck Manual)
- Skin infection = up to 35 mg/kg q12h, treat 14–21 days minimum
- Urinary tract = 12–25 mg/kg q12h, treat 7–14 days
- Senior with CKD = reduce dose 20–30%, monitor creatinine
- Suspension = 125 mg/5 mL = 25 mg/mL (1 mL = 25 mg)
- Capsules = 250 mg and 500 mg, split for small cats
- Peak plasma = 1.8 hours after oral dose
- Cross-reactivity = 1–3% in penicillin-allergic cats