Cephalexin For Cats Dosage Calculator

Calculate the right cephalexin dosage for your cat based on weight, dose base, and drug type.

Last updated: June 2, 2026
Frank Zhao - Creator
CreatorFrank Zhao
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📍 The calculated dosage is based on the MSD Manual recommendations.
1Amount per dose
dosage=dose base×weight\text{dosage} = \text{dose base} \times \text{weight}
2Daily dosage
dailyDosage=2×dose base×weight\text{dailyDosage} = 2 \times \text{dose base} \times \text{weight}
3Liquid per dose
volume=dosagedrug strength\text{volume} = \frac{\text{dosage}}{\text{drug strength}}
4~Tablets per dose
number=⌊dosageform+0.2⌋\text{number} = \left\lfloor \frac{\text{dosage}}{\text{form}} + 0.2 \right\rfloor
weightCat's weight (kg)
doseBaseDose base (mg/kg)
dosageAmount per dose (mg)
dailyDaily dosage (mg)
formDrug type strength
volumeLiquid per dose (mL)

What is cephalexin?

Cephalexin is an antibiotic that belongs to the cephalosporin class of antimicrobial agents. It is classified as a first-generation cephalosporin and is used to treat bacterial infections in animals, including cats and dogs. Veterinarians often prescribe it to treat skin, soft tissue, bone, and urinary tract infections caused by different types of bacteria.

Like penicillin, cephalexin is also classified as a beta-lactam antibiotic. This means that cephalexin, like penicillin, kills bacteria by interfering with cell wall formation. Cephalexin leads the bacteria to a quick death by weakening the cell wall and making it more susceptible to outside pressures. Cephalexin is primarily effective against gram-positive bacteria and some gram-negative bacteria.

Important note on resistance

⚠️ The use of cephalexin has been on the rise, and with that, the amount of resistant bacteria is also increasing. The Antimicrobial Advice Ad Hoc Expert Group (AMEG) has given a category C to this type of antibiotic. This means that it should only be used by veterinarians when there is no better and safer alternative.

First-generation cephalosporins, like cephalexin, are ineffective against Enterococcus spp, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus and, in the case of cephalexin specifically, E. coli. They also tend to be ineffective against anaerobic bacteria.

Cephalexin, sometimes sold under brand names such as Keflex® or Rilexene®, is available in various formulations, including capsules and oral suspension. So far, the FDA (Food and Drug Administration in the US) has only approved Rilexene® for dogs. However, cephalexin is safe for cats (when administered at the appropriate dose) and is widely used by most veterinarians.

Learn more about dogs

To learn more about what cephalexin is for dogs, you can check out our cephalexin for dogs dosage calculator.

How much cephalexin can you give a cat?

The amount of cephalexin you give to your cat will depend on your cat's weight and the condition being treated; usually, one single dose is no less than 15 mg/kg and no more than 35 mg/kg. Remember, however, that many other factors may contribute to this decision, and giving cephalexin to cats without a vet prescription is not advised; let's not risk a cephalexin cat overdose!

Cephalexin for cats: dosage chart

As mentioned above, the recommended cephalexin dosage will vary according to your cat's weight and condition. Below is a simple dosage chart of cephalexin for cats showing the most common dosages.

Weight (kg)Weight (lb)Single dose (15 mg/kg)Single dose (20 mg/kg)Single dose (35 mg/kg)
12.2152035
24.4304070
36.64560105
48.86080140
511.075100175
613.290120210
715.4105140245
817.6120160280
919.8135180315
1022.0150200350

To determine the most suitable dose for your cat, down to the decimals, use our cephalexin for cats dosage calculator. Input your cat's weight, dosage base, and drug type, and see the calculator do its magic!

More pet dosage tools

If you like this tool, then you should probably also take a look at our omega-3 for dogs calculator and our metacam dosage calculator for dogs.

How to use the cephalexin for cats dosage calculator

Using the cephalexin for cats dosage calculator couldn't be easier. All you have to do is:

1

Input your cat's weight

Let's say it is 2 pounds (0.91 kg).

2

Input the dosage base

Enter the dosage base recommended by your vet; let's assume it is 15 mg/kg.

3

Choose the drug type

Select the preferred drug type; in this case, it will be liquid (125 mg/5 mL).

4

Get your results

The calculator will automatically display the amount per dose (13.6 mg) and the daily dosage (27 mg) of cephalexin, as well as the amount of medicine per dose (0.5 mL) and per day (1 mL).

Reverse calculation

In case all you have is the amount per dose or the daily dosage, and you want to know whether that is ok for your cat:

  1. Empty the dosage base field.
  2. Input your cat's weight.
  3. Input the amount per dose or the daily dosage.

The calculator will tell you what dosage base it is equivalent to. If the dosage is too low or too high, a warning message will appear.

Side effects of cephalexin for cats

Yes, cats can take cephalexin, but that doesn't mean this drug has no risks. Although cephalexin is considered to be relatively safe, cephalexin for cats has some side effects that you should be aware of:

Vomiting

Cats may experience vomiting shortly after administration of cephalexin. While this usually does not indicate a severe issue, it suggests the cat may be sensitive to the drug. Giving the drug with some food may alleviate this side effect.

Hypersensitivity reactions

Cats can experience allergic reactions to cephalexin, which may manifest as a rash, hives, scratching, facial swelling, or irregular breathing. If signs of an allergic reaction occur, immediate veterinary attention is necessary.

It has also been reported that cats may suffer from fever, diarrhea, decreased appetite, drooling and lethargy, and increased activity.

When NOT to give cephalexin

You shouldn't give cephalexin to your cat if:

  • Your cat is allergic to beta-lactams antibiotics (e.g., penicillin or amoxicillin).
  • Your cat has a renal dysfunction and/or is receiving other nephrotoxic drugs.

Furthermore, it has been reported that high doses or very prolonged use have been associated with neurotoxicity, neutropenia, agranulocytosis, thrombocytopenia, hepatitis, positive Coomb's test, interstitial nephritis, and tubular necrosis.

To prevent an overdose, make sure not to give cephalexin to your cat without a vet prescription! You can also check whether the prescribed dosage matches those recommended by the MSD Manual by using our cephalexin for cats dosage calculator.

Is human cephalexin safe for cats?

Yes, human cephalexin is safe for cats. However, it's always advisable to opt for the drug formulations made explicitly for them. This ensures precise dosing without needing adjustments, safeguarding your cat from potential overdoses and ineffective treatments.

Learn more about your cat's age

Now, if you want to know how your age compares to your cat's, our cat age calculator has the answer for you.

FAQs

How do I calculate the appropriate dosage of cephalexin for a 5-pound cat?

To calculate the appropriate dosage of cephalexin for a 5-pound cat, you must:

  1. Convert 5 pounds to kg: 5×0.453592≈2.2685 \times 0.453592 \approx 2.268
  2. Multiply your cat's weight by the prescribed basic dose to find how much is one single dose. Assuming a basic dosage of 15 mg/kg: 2.268 kg×15 mg/kg=34.02 mg2.268 \, \text{kg} \times 15 \, \text{mg/kg} = 34.02 \, \text{mg}
  3. Multiply the result you obtained by 2, to obtain the total daily dose: 34.02 mg×2=68.04 mg34.02 \, \text{mg} \times 2 = 68.04 \, \text{mg}

That's it! You now know how much cephalexin per day your cat should take.

Can cats take cephalexin?

Yes, cats can take cephalexin. However, you should always stick to the dosage recommended by your vet. If you give your pet a dosage that is too low or too high, you risk the medicine not taking effect or, worse, putting your pet's life in danger due to an overdose!

Can I give my cat cephalexin 250 mg?

No, unless we are talking about a Maine Coon who is over the 13-pound (about 6 kg) threshold, cephalexin 250 mg will probably be too intense for your cat. However, if the question were “Can I give my cat cephalexin 250 mg/5 mL?” the answer would be “Yes”. As this is a liquid form of cephalexin, it is possible to adjust it to the dose required by your pet better.

Can I give my cat cephalexin 500 mg?

No, you cannot give your cat cephalexin 500 mg. For most cats, that would mean an overdose with very unpleasant side effects or, in some cases, even death. Unless stated explicitly by your vet, do not give your cat cephalexin 500 mg.

Limitations & sources

Not medical advice

This calculator is for informational purposes only. It does not diagnose conditions or replace an examination by a licensed veterinarian. Always consult with your vet before administering any medication to your pet.

Individual cats may vary in their response to medication. Factors such as age, kidney function, concurrent medications, and overall health status can affect the appropriate dosage.

References & further reading

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Cephalexin For Cats Dosage Calculator