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First-Generation Cephalosporin Antibiotic · For Cats

Cephalexin dosage reference for cats (Keflex)

This page's standard weight-based reference is 15 mg per kg (6.80 mg per lb), with Every 8-12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your cat's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset
1-2 hours
Duration
8-12 hours per dose
Class
First-Generation Cephalosporin Antibiotic

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Cephalexin (often known by brand names such as Keflex and Rilexine) is a first-generation cephalosporin antibiotic commonly used in veterinary medicine for Skin and soft tissue infections, Urinary tract infections, Wound infections, Bone infections, and Respiratory infections. Understanding the correct dosage, administration, and potential side effects of Cephalexin is critical for your cat’s safety and well-being.

A typical Cephalexin dose for cats is around 15 mg/kg Every 8-12 hours, within a usual range of 10-25 mg/kg. Available forms include Capsule, Tablet, and Oral suspension.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Cephalexin Dosage Calculator for Cats

Enter your cat’s weight below to estimate the Cephalexin dose from the 15 mg/kg guideline. Your veterinarian may adjust it for your cat’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your cat's weight

Quick Dosage Chart

Typical Cephalexin amounts for common cat weights, for quick reference:

Dosage Chart · 02

Keflex weight-based reference chart for cats

Scroll sideways to see full table

Weight Lower Reference Standard Reference Upper Reference Frequency
3 lbs (1.4 kg) 14.0 mg 21.0 mg 35.0 mg Every 8-12 hours
4 lbs (1.8 kg) 18.0 mg 27.0 mg 45.0 mg Every 8-12 hours
5 lbs (2.3 kg) 23.0 mg 34.5 mg 57.5 mg Every 8-12 hours
6 lbs (2.7 kg) 27.0 mg 40.5 mg 67.5 mg Every 8-12 hours
7 lbs (3.2 kg) 32.0 mg 48.0 mg 80.0 mg Every 8-12 hours
8 lbs (3.6 kg) 36.0 mg 54.0 mg 90.0 mg Every 8-12 hours
9 lbs (4.1 kg) 41.0 mg 61.5 mg 102.5 mg Every 8-12 hours
10 lbs (4.5 kg) 45.0 mg 67.5 mg 112.5 mg Every 8-12 hours
12 lbs (5.4 kg) 54.0 mg 81.0 mg 135.0 mg Every 8-12 hours
14 lbs (6.3 kg) 63.0 mg 94.5 mg 157.5 mg Every 8-12 hours
16 lbs (7.3 kg) 73.0 mg 109.5 mg 182.5 mg Every 8-12 hours
18 lbs (8.2 kg) 82.0 mg 123.0 mg 205.0 mg (250mg tablet) Every 8-12 hours
20 lbs (9.1 kg) 91.0 mg 136.5 mg 227.5 mg (250mg tablet) Every 8-12 hours
25 lbs (11.3 kg) 113.0 mg 169.5 mg 282.5 mg (250mg tablet) Every 8-12 hours

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Keflex reference by cat weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Cephalexin to Your Cat

Cephalexin capsules can be given whole, hidden inside a pill pocket or a small piece of deli meat or cheese. Do not open the capsule, as the powder inside tastes very unpleasant. If your cat refuses capsules, ask about the oral liquid suspension, which can be flavored. Use a pill gun to place the capsule at the back of your cat’s tongue, hold the mouth closed, and stroke the throat until you see a swallow. Follow with a small syringe of water to ensure it goes down. Always give with food to reduce stomach upset. Complete the full course as prescribed.

It is generally recommended to give Cephalexin with food to help reduce stomach upset. It may interact with Aminoglycoside antibiotics (increased nephrotoxicity), Probenecid (increased cephalexin levels), Antacids (reduced absorption if given simultaneously), and Nephrotoxic drugs (additive kidney strain).

Side Effects and Safety

Common side effects include Nausea and vomiting, Diarrhea, Decreased appetite, and Drooling (if capsule is bitten). More serious side effects can occur, such as Severe allergic reaction (anaphylaxis), Persistent bloody diarrhea, Kidney damage (rare, at very high doses), and Blood disorders (rare).

Cautions · 12

When Keflex should be used with caution or avoided

Some cats should not take Keflex, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Keflex.

  • Known allergy to cephalosporins or penicillins
  • Severe kidney impairment (dose adjustment needed)
  • History of antibiotic-associated colitis

Interactions · 13

Keflex drug interactions

Keflex can interact with other drugs. This list is not complete — always give your veterinarian a full list of your cat's medications and supplements.

Aminoglycoside antibiotics (increased nephrotoxicity)
Probenecid (increased cephalexin levels)
Antacids (reduced absorption if given simultaneously)
Nephrotoxic drugs (additive kidney strain)

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult cat at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

  • In an emergency, or after accidental ingestion or a suspected overdose
  • For pregnant or nursing pets
  • For very young or very old cats
  • For pets with liver disease, kidney disease, or another chronic illness
  • For pets taking several medications at once
  • When you are not sure of your cat's current, accurate weight
  • For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your cat had too much Keflex, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

  • Call your veterinarian or the nearest emergency animal hospital.
  • ASPCA Animal Poison Control Center: (888) 426-4435
  • Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

Is cephalexin safe for cats?
Yes, cephalexin is generally considered safe and well-tolerated in cats. It is a first-generation cephalosporin antibiotic commonly prescribed for bacterial infections. Side effects are typically mild and mostly gastrointestinal (nausea, diarrhea). It is one of the safer antibiotic choices for cats when used at the correct dose and duration prescribed by your vet.
How long should my cat take cephalexin?
The typical course of cephalexin for cats is 7-14 days for most infections, though deep skin infections or bone infections may require 4-6 weeks or longer. It is very important to complete the entire course even if your cat appears better, as stopping early can lead to antibiotic resistance and recurrence of the infection.
Can I give my cat human cephalexin?
The active ingredient in human cephalexin is the same as veterinary formulations. However, you should never give your cat any medication without veterinary guidance, as the dose must be calculated specifically for your cat's weight and condition. Human capsules may also contain inactive ingredients not tested in cats. Always obtain antibiotics through your veterinarian.
What infections does cephalexin treat in cats?
Cephalexin is effective against many gram-positive bacteria and some gram-negative bacteria. In cats, it is commonly used for skin infections (wounds, abscesses, pyoderma), urinary tract infections, respiratory infections, and bone infections. It is not effective against all types of bacteria, so your vet may perform a culture and sensitivity test to confirm it is the right antibiotic.
What if my cat vomits after taking cephalexin?
Mild nausea is a common side effect. Giving cephalexin with food usually helps prevent vomiting. If your cat vomits within 30 minutes of dosing, you may need to re-dose—ask your vet. If vomiting persists despite giving with food, contact your vet about switching to a different antibiotic or trying a compounded formulation that may be easier on the stomach.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your cat's weight by the lower, standard, and upper mg/kg values recorded for Keflex. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses
Skin and soft tissue infections, Urinary tract infections, Wound infections, Bone infections, Respiratory infections
Recorded forms
Capsule, Tablet, Oral suspension
Reference timing
Every 8-12 hours; onset 1-2 hours; duration 8-12 hours per dose

Individual checks a calculator cannot perform

  • Confirm the diagnosis and the reason this medication is being considered.
  • Match the exact product, concentration, route, and whether a tablet may be split.
  • Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
  • Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

Known allergy to cephalosporins or penicillins; Severe kidney impairment (dose adjustment needed); History of antibiotic-associated colitis.

Recorded interactions

Aminoglycoside antibiotics (increased nephrotoxicity); Probenecid (increased cephalexin levels); Antacids (reduced absorption if given simultaneously); Nephrotoxic drugs (additive kidney strain).

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your cat's complete medication list before acting on a number.

For Dogs

Looking for Cephalexin dosage for dogs?

View the Cephalexin dosage chart and calculator for dogs.

Related · 08

Related medications for cats

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 15 mg per kg (6.80 mg per lb) of body weight, given Every 8-12 hours. The calculator multiplies that basis by your cat's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner
Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status
Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review cats dosage data.

Safety · 10

More resources