What is cephalexin?
Cephalexin is an antibiotic belonging to the first-generation cephalosporin class of beta-lactam antimicrobials. Like penicillin, it works by interfering with bacterial cell wall formation, causing bacteria to weaken and die. It is primarily effective against gram-positive bacteria and some gram-negative bacteria. Veterinarians prescribe it to treat skin, soft tissue, bone, and urinary tract infections in cats.
Cephalexin is sometimes sold under brand names such as Keflex® or Rilexene®. While the FDA has only approved Rilexene® for dogs, cephalexin is widely used by veterinarians for cats and is considered safe when administered at the appropriate dose.
⚠️ We try to do our best when creating our calculators — however, you must remember that they cannot replace actual medical advice and cannot serve as a sole source of clinical decisions. Contact your vet if you have any questions.
How much cephalexin can you give a cat?
The amount of cephalexin you give to your cat depends on its weight and the condition being treated. The recommended single dose is generally 15–35 mg/kg given twice daily (every 12 hours). Our calculator uses:
- Urinary Tract Infection (UTI): 15 mg/kg per dose
- Skin Infection: 22 mg/kg per dose
- General Use: 15 mg/kg per dose
Always follow your veterinarian's prescription — do not give cephalexin to your cat without a vet consultation.
Cephalexin for cats: dosage chart
Below is a reference dosage chart for cats at 15 mg/kg (UTI / general use):
| Cat Weight (lbs) | Cat Weight (kg) | Dose per admin (mg) | Capsule 250 mg | Capsule 500 mg | Liquid (mL) |
|---|---|---|---|---|---|
| 4.4 lbs | 2 kg | 30 mg | 0.12 | 0.06 | 1.2 mL |
| 6.6 lbs | 3 kg | 45 mg | 0.18 | 0.09 | 1.8 mL |
| 8.8 lbs | 4 kg | 60 mg | 0.24 | 0.12 | 2.4 mL |
| 11 lbs | 5 kg | 75 mg | 0.30 | 0.15 | 3.0 mL |
| 13.2 lbs | 6 kg | 90 mg | 0.36 | 0.18 | 3.6 mL |
| 15.4 lbs | 7 kg | 105 mg | 0.42 | 0.21 | 4.2 mL |
How to use the cephalexin for cats dosage calculator
- Select your measurement system — Imperial (lbs) or Metric (kg).
- Enter your cat's weight.
- Choose the indication (UTI, skin infection, or general use).
- Optionally select a tablet form (250 mg, 500 mg, or liquid) and enter the price per unit in your preferred currency to estimate treatment cost.
- Click Calculate to get the dose per administration, daily dose, and full 14-day course amounts.
Side effects of cephalexin for cats
Possible side effects include:
- Vomiting and diarrhea — most common; giving cephalexin with food may help
- Loss of appetite
- Drooling or foaming at the mouth — especially if the cat tastes the capsule
- Allergic reactions — rash, swelling, or difficulty breathing (seek vet care immediately)
- Lethargy
Is human cephalexin safe for cats?
Human cephalexin (e.g., Keflex) is used off-label in cats and is generally considered safe when properly dosed under veterinary supervision. However, never give your cat human medication without explicit veterinary guidance. The dosage form and inactive ingredients in human products may differ from veterinary formulations.
FAQs
- Can I give my cat cephalexin 500 mg?
- A 500 mg capsule is typically too large for most cats. For a 5 kg cat needing 75 mg per dose, you would need only 0.15 of a 500 mg capsule. Your vet may prescribe compounded lower-dose formulations or liquid suspension instead.
- How long does it take for cephalexin to work in cats?
- Most cats show improvement within 48–72 hours. However, complete the full course (usually 14 days) even if your cat seems better, to prevent antibiotic resistance.
- Can I give my cat cephalexin without a vet prescription?
- No. Cephalexin is a prescription antibiotic. Always obtain a diagnosis and prescription from a licensed veterinarian to ensure correct dosing and avoid a cephalexin cat overdose.
- What is the difference between cephalexin for cats and dogs?
- The active ingredient is the same; however, cats generally require lower absolute doses due to their smaller body weight. Skin infection doses may also differ slightly — 22 mg/kg is commonly used for cats vs. 20 mg/kg for dogs.
- How to prevent a cephalexin cat overdose?
- Always follow the veterinarian's prescribed dose. Use our calculator only as a reference, not a substitute for professional advice. If you suspect an overdose (excessive drooling, tremors, seizures), contact your vet or an emergency animal clinic immediately.