The dose is milligrams per kilogram of the cat
Cephalexin (Keflex, Rilexine) is dosed by body weight, typically 15 to 30 mg/kg every 12 hours by mouth. A 4 kg cat at 25 mg/kg gets 100 mg per dose, twice a day. The right mg/kg depends on what is being treated, so this figure is for confirming a prescription, not replacing your vet.
Typical mg/kg by infection type
| Infection | Dose (mg/kg) | Interval |
|---|---|---|
| Skin / soft tissue | 22–35 | every 12 h |
| Urinary tract | 12–25 | every 12 h |
| Other susceptible infections | 10–15 | every 6–8 h |
| Senior / reduced kidney function | minus 20–30% | as directed |
Ranges follow the Merck Veterinary Manual. Cephalexin is used off-label in cats, so the vet chooses the value.
Turning the dose into a tablet or a volume
- Common weights. A 4 kg adult at 25 mg/kg is 100 mg; a 5 kg cat is 125 mg; a 6 kg cat is 150 mg per dose.
- Tablets. Come as 250 mg and 500 mg. Divide the dose by the strength — 125 mg is half a 250 mg tablet.
- Liquid. Suspension at 125 mg per 5 mL suits small cats: 100 mg is 4 mL. Give with food if your cat vomits after a dose.
- Finish the course. Keep going 5 to 7 days past the point symptoms clear, or the full course your vet set, even if the cat looks better.
Common questions
How much cephalexin does a cat need per dose?
Veterinary references put the range at 15 to 30 mg per kilogram of body weight, given every 12 hours by mouth. For skin and soft-tissue infections the higher end (22 to 35 mg/kg) is common; urinary infections often use less. Your vet sets the exact number for the specific infection.
How do I turn the dose into tablets?
Divide the per-dose milligrams by the tablet strength. A 5 kg cat at 25 mg/kg needs about 125 mg, which is half a 250 mg tablet. Liquid suspension (125 mg per 5 mL) is easier to split for small cats.
When should the dose be reduced?
Older cats or cats with reduced kidney function usually need the dose cut by 20 to 30 percent or the interval stretched. Cephalexin is cleared by the kidneys, so impaired kidneys let it build up. This is a decision for your vet, not a guess.
