Cephalexin for Cats Dosage Calculator
Enter your cat's weight and your vet's prescribed dose rate to find exactly how much cephalexin to give per dose and per day. Choose your preferred tablet or liquid formulation and the dosing frequency your vet recommended. Results update instantly in metric or imperial units.
What is cephalexin and why is it prescribed for cats?
Cephalexin is a first-generation cephalosporin antibiotic that works by disrupting bacterial cell-wall synthesis, which kills the bacteria outright (bactericidal action). It is active against many gram-positive bacteria, including Staphylococcus and Streptococcus species, that commonly cause skin infections (pyoderma), wound infections, and urinary tract infections in cats. It is also used for soft-tissue infections and some bone infections. Because it is given orally and is reasonably well tolerated, it is one of the most commonly dispensed antibiotics in small-animal veterinary practice. Cephalexin is not effective against gram-negative bacteria such as Pseudomonas, so your vet will base their choice on a culture and sensitivity result where possible.
How is the cephalexin dose for cats calculated?
The dose is always calculated on a per-kilogram basis. The standard range cited in veterinary references (including the MSD Veterinary Manual and Plumb's Veterinary Drug Handbook) is 15-35 mg per kilogram of body weight per dose. The most common prescription is around 20-22 mg/kg, which roughly corresponds to 10 mg/lb. Your vet may choose a rate toward the lower end for mild skin infections and toward the higher end for deeper infections, urinary tract infections, or cases caused by less susceptible organisms. Dosing frequency is typically every 12 hours (twice daily) for skin and soft-tissue conditions and every 8 hours (three times daily) for urinary or bone infections. This calculator does the arithmetic for you: it multiplies your cat's weight in kilograms by the dose rate to give the single-dose milligram total, then multiplies again by the number of doses per day.
Choosing the right formulation: tablets versus liquid
Cephalexin is available as standard tablets (250 mg), flavored chewable tablets (75 mg, 150 mg, and 300 mg sizes), and oral liquids that are typically dispensed as 125 mg/5 mL or 250 mg/5 mL suspensions. For larger cats the 250 mg tablet is practical because many doses fall near one whole tablet. Chewable tablets in smaller strengths are useful for cats that are difficult to pill, since they can be hidden in a treat. Liquid suspensions allow precise dosing in small or very light cats where tablet fractions would be too small to split accurately. Once you select the formulation, this calculator converts the milligram dose into the appropriate number of tablets or milliliters of liquid.
Side effects and what to watch for
Cephalexin is generally well tolerated in cats, but the most common side effect is gastrointestinal upset, including nausea, vomiting, and loose stools. Giving the dose with a small amount of food usually reduces stomach irritation. Rare but serious reactions include hypersensitivity (allergic response), which may appear as facial swelling, hives, or severe lethargy. Cats with a known allergy to penicillins have a small risk of cross-reactivity with cephalosporins. If you notice any signs of an allergic reaction, stop the medication and contact your vet immediately. In cats with reduced kidney function, the dose may need to be adjusted because cephalexin is primarily eliminated by the kidneys. Always complete the entire prescribed course even if your cat appears to have recovered, since stopping antibiotics early promotes bacterial resistance and can allow the infection to relapse.
Cephalexin dosage by cat weight (20 mg/kg, q12h)
| Cat weight (kg) | Cat weight (lb) | Single dose (mg) | Daily dose (mg) |
|---|---|---|---|
| 1 | 2.2 | 20 | 40 |
| 1.5 | 3.3 | 30 | 60 |
| 2 | 4.4 | 40 | 80 |
| 2.5 | 5.5 | 50 | 100 |
| 3 | 6.6 | 60 | 120 |
| 3.5 | 7.7 | 70 | 140 |
| 4 | 8.8 | 80 | 160 |
| 4.5 | 9.9 | 90 | 180 |
| 5 | 11 | 100 | 200 |
| 5.5 | 12.1 | 110 | 220 |
| 6 | 13.2 | 120 | 240 |
| 7 | 15.4 | 140 | 280 |
| 8 | 17.6 | 160 | 320 |
Estimated doses at a common mid-range rate of 20 mg/kg given twice daily. Your vet may prescribe a different rate. Values are for guidance only.
Frequently asked questions
What is the standard cephalexin dose for cats?
The standard dose is 15-35 mg per kilogram of body weight per dose, given every 8 or 12 hours depending on the type of infection. A common mid-range prescription is about 20 mg/kg twice daily. For example, a 4 kg cat at 20 mg/kg receives 80 mg per dose and 160 mg per day. Your vet will specify the exact rate and frequency based on your cat's condition.
How often should I give cephalexin to my cat?
Most commonly every 12 hours (twice daily) for skin and soft-tissue infections, or every 8 hours (three times daily) for urinary tract or bone infections. The dosing interval your vet prescribes depends on the severity and site of infection, and on the susceptibility of the bacteria involved. Always follow your vet's specific instructions rather than assuming a dosing schedule.
Can I give my cat a human cephalexin capsule?
Cephalexin itself is the same molecule regardless of whether it is marketed for humans or animals, so the drug content is identical. However, human capsules are typically 500 mg, which is much larger than a typical cat dose, and splitting capsules accurately is very difficult. Veterinary-formulated tablets in smaller strengths or flavored liquids make dosing far more precise. Always consult your vet before using a human formulation for your cat.
How long does cephalexin treatment last for cats?
Treatment duration depends on the type and severity of infection. Superficial skin or wound infections are commonly treated for 7-14 days. Urinary tract infections typically require 10-14 days. Deep tissue or bone infections may require 4-6 weeks. Complete the full course as prescribed even if your cat appears better before it ends.
Should cephalexin be given with food?
Cephalexin can be given with or without food. Giving it with a small meal reduces the likelihood of nausea or vomiting. If your cat consistently vomits after receiving the dose on an empty stomach, try administering it alongside food. Food does not meaningfully reduce the absorption of cephalexin in cats.
What happens if I miss a dose?
Give the missed dose as soon as you remember. However, if it is almost time for the next scheduled dose, skip the missed one and continue with the regular schedule. Never double up to compensate for a missed dose. Try to dose at evenly spaced times throughout the day to maintain consistent drug levels in your cat's blood.