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Cephalexin for Cats Dosage Calculator

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Plumb's Cat-Specific Dose.
6 Drug Forms.
8 Reference Breeds.
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How it Works

01Enter Cat Weight

Use current body weight (kg or lb). Cephalexin scales linearly with weight.

02Set Dose (Default 25 mg/kg)

Plumb's range is 22-30 mg/kg every 12 hours. Cap 60 mg/kg/day across all doses.

03Pick Drug Form

6 forms: 250 mg tablets, 75 / 150 / 300 mg chewables, 125 or 250 mg/5 mL liquid.

04Get mg + Units / Dose

Per-dose mg, exact mL of liquid or fraction of tablet, daily total, vet-grade safety bands.

What is a Cephalexin for Cats Dosage Calculator?

Cephalexin is a first-generation cephalosporin antibiotic widely prescribed to cats for skin infections, abscesses (the most common feline infection — typically from cat fights), urinary tract infections, soft-tissue infections, and post-surgical prophylaxis. Our Cephalexin for Cats Dosage Calculator implements the cat-specific Plumb's Veterinary Drug Handbook dose: 22-30 mg/kg PO every 12 hours, with default 25 mg/kg Q12H. Enter your cat's weight, customise the dose strength if needed, pick from 6 cat-appropriate commercial formulations, and instantly get the per-dose mg, exact mL of liquid or fraction of tablet/chewable, daily total in both mg and mg/kg (capped at 60 mg/kg/day in cats), and a 5-band size classification.

The calculator covers the 6 commercial formulations practical for cat-sized doses: 250 mg tablets (often too large for typical cats — usually halved or quartered for medium / small cats), 75 / 150 / 300 mg flavoured chewables (the best fit for most cats — Rilexine brand), and 125 or 250 mg / 5 mL oral suspension liquid (BEST option for very small cats and exact sub-tablet dosing). The 500 mg dog tablets and 600 mg chewables are excluded — they are impractical for cat-sized doses without complex splitting.

Designed for cat owners verifying a vet prescription, vet techs and nurses preparing dispensed medication, multi-cat households where each cat needs an individual dose calculation, and emergency-clinic phone triage, the tool runs entirely in your browser — no account, no data stored. Critical safety: cephalexin is a prescription antibiotic — always confirm dose with your veterinarian. Complete the full prescribed course (typically 7-21 days for skin / abscess, 7-14 days for UTI) even if symptoms resolve early; early discontinuation is the #1 cause of antibiotic resistance. Cephalexin is NOT effective against Pseudomonas, anaerobes, mycoplasma, or methicillin-resistant Staphylococci (MRSP, MRSA) — culture-and-sensitivity testing is needed if no improvement in 5-7 days.

Pro Tip: Pair this with our Cat BMI Calculator for body-condition assessment, our Cat Benadryl Dosage Calculator for managing concurrent allergic itch, or our Cephalexin for Dogs Dosage Calculator for the canine equivalent in multi-pet households.

How to Use the Cephalexin for Cats Dosage Calculator?

Enter Your Cat's Current Weight: Use weight from a recent vet visit. Most adult cats weigh 3-7 kg (6.5-15 lb). Cephalexin scales linearly with weight, so an inaccurate weight directly translates to inaccurate dosing. Use ACTUAL body weight, not ideal weight.
Set Dose Base (Default 25 mg/kg): Plumb's standard cat range is 22-30 mg/kg per administration. The 25 mg/kg default is the conservative middle of the range. Use 22 mg/kg for uncomplicated infections; 30 mg/kg for severe deep infections or resistant cases. NEVER exceed 30 mg/kg per single dose, and NEVER exceed 60 mg/kg/day total in cats (more conservative than the dog cap of 90 mg/kg/day).
Pick the Drug Form: 6 cat-appropriate options. Liquid (125 mg/5 mL = 25 mg/mL): BEST option for most cats — exact mL dosing with an oral syringe. Liquid (250 mg/5 mL = 50 mg/mL): for medium-large cats needing higher concentrations. Chewables (75 / 150 / 300 mg): flavoured tablets, easier than pills for most cats; choose strength matching the per-dose mg. Tablets (250 mg): cheapest generic option, typically halved or quartered for cats.
Apply Dose × Weight = mg/dose: The calculator multiplies dose (mg/kg) × weight (kg) = mg per dose. Then divides by drug strength to get tablets / chewables / mL per dose, multiplies by 2 (Q12H frequency) for daily total.
Read Per-Dose mg + Daily Total + Cap Status: Per-dose mg, units per dose in your chosen form, daily total in mg, daily mg/kg/day (compared to the 60 mg/kg/day cat cap). Pay attention to the warnings panel — common flags are sub-microliter liquid doses (P200 accuracy threshold), 250 mg tablets too large for small cats, and impractical fractional doses (round to ¼ or ½).
Use a 1 mL or 3 mL Oral Syringe for Liquid: Oral syringes give CV < 5% accuracy; kitchen teaspoons vary 4-7 mL with no precision. For most cats on cephalexin liquid, the dose is 2-6 mL of 125 mg/5 mL — use a 3 mL or 5 mL oral syringe. Available free at vet clinics; pharmacies sell them for $1-$2.
Give With Food, Complete the Full Course: Cephalexin is well-absorbed with or without food, but giving with a small treat reduces vomiting and gastric upset. Complete the full prescribed course (7-21 days) even if symptoms resolve early — stopping early is the #1 cause of antibiotic resistance.

How is the cat cephalexin dose calculated?

Cephalexin dosing in cats is simple weight-based pharmacology — multiply mg/kg by body weight in kg to get mg per dose, then divide by drug strength to get units per dose. The cat dose range (22-30 mg/kg Q12H) is identical to the dog range, but the daily cap is more conservative (60 mg/kg/day cats vs 90 mg/kg/day dogs).

Standard veterinary range from Plumb's Veterinary Drug Handbook (10th ed., 2023), cross-referenced with the ACVIM Antimicrobial Use Guidelines and the ISCAID Pyoderma Consensus.

Core Formula

For a cat of weight W (kg) at dose strength D (mg/kg) given Q12H (twice daily):

Per-dose mg = D × W

Per-dose mL (liquid 125 mg/5 mL = 25 mg/mL) = (D × W) / 25

Per-dose tablets/chewables = (D × W) / strength_mg

Daily total mg = D × W × 2 (must NOT exceed 60 mg/kg/day in cats)

Cat-Specific Dose Range

  • Standard: 25 mg/kg PO Q12H (calculator default).
  • Range: 22-30 mg/kg PO every 12 hours.
  • Maximum daily total: ≤ 60 mg/kg/day (cat-specific — more conservative than the 90 mg/kg/day dog cap).
  • Common indications: superficial pyoderma, deep pyoderma, skin abscesses (most common — usually from cat-fight wounds), uncomplicated UTI, soft-tissue infections, post-surgical prophylaxis.

Commercial Formulations and Cat Suitability

  • Tablets, 250 mg: generic — too large for typical cats (a 4 kg cat at 25 mg/kg needs only 100 mg = 2/5 of a tablet). Practical only for medium-large cats with halving (½ tab = 125 mg) or quartering. Cheapest per dose.
  • Chewables, 75 mg (Rilexine): ideal for very small cats (1.5-3 kg at 22-25 mg/kg = 33-75 mg, ~1 chewable).
  • Chewables, 150 mg (Rilexine): ideal for small-medium cats (3-6 kg at 25 mg/kg = 75-150 mg, ~½ to 1 chewable).
  • Chewables, 300 mg (Rilexine): for large cats (6+ kg at 25 mg/kg = 150+ mg, ½ chewable up).
  • Oral suspension, 125 mg / 5 mL = 25 mg/mL: THE BEST OPTION for cats. Exact mL dosing with an oral syringe. For a 4 kg cat at 25 mg/kg: dose = 100 mg = 4 mL. Available OTC by Rx.
  • Oral suspension, 250 mg / 5 mL = 50 mg/mL: for medium-large cats (lower volume per dose).

Worked Example — Average Cat

A 4.5 kg domestic shorthair with a fight-wound abscess, 25 mg/kg Q12H × 14 days using 125 mg/5 mL liquid:

  • Per-dose mg: 25 × 4.5 = 112.5 mg.
  • Liquid mL: 112.5 / 25 = 4.5 mL of children's liquid per dose.
  • Daily total: 112.5 × 2 = 225 mg/day = 50 mg/kg/day. Under the 60 mg/kg/day cap.
  • 14-day course: 14 × 9 mL = 126 mL liquid = about one 4 oz (118 mL) bottle.
  • Cost: ~$15-$25 for the full course (generic).

When Cephalexin Works (And When It Doesn't)

  • Excellent activity (first-line): Staphylococcus pseudintermedius (the dominant feline skin pathogen — over 80% of cat pyoderma), Streptococcus canis, beta-hemolytic streptococci, methicillin-susceptible Staph aureus, susceptible Pasteurella multocida (the dominant bacterium in cat-bite abscesses).
  • Moderate activity: susceptible E. coli (50-70% of feline UTI isolates), Proteus mirabilis, Klebsiella pneumoniae (variable).
  • POOR / NO activity: Methicillin-resistant Staphylococcus pseudintermedius (MRSP), MRSA, Enterococcus, Pseudomonas aeruginosa, anaerobes (most), Mycoplasma, all atypical pathogens, all fungi.
Real-World Example

Cephalexin for Cats Dosage – Worked Examples

Example 1 — Standard Cat Abscess (Domestic Shorthair). 4.5 kg DSH with a cat-bite abscess, 25 mg/kg Q12H × 10 days using 125 mg/5 mL liquid.
  • Per-dose: 25 × 4.5 = 112.5 mg = 4.5 mL of liquid.
  • Daily total: 225 mg/day = 50 mg/kg/day (under 60 mg/kg/day cap).
  • 10-day course: 90 mL liquid = ~3/4 of a 4 oz (118 mL) bottle.
  • Confirm abscess is open / drained — antibiotic alone is inadequate for closed abscesses; vet must lance and flush first.

Example 2 — Small Cat UTI (Siamese). 3 kg Siamese with culture-confirmed E. coli UTI, 22 mg/kg Q12H × 14 days using 75 mg chewable.

  • Per-dose: 22 × 3 = 66 mg ≈ 1 × 75 mg chewable (slightly over-dosed but acceptable).
  • OR: 66 mg = 2.6 mL of 125 mg/5 mL liquid (more accurate).
  • Daily total: 132-150 mg/day (depending on form rounding) = 44-50 mg/kg/day.
  • 14-day course: 28 chewables OR 37 mL liquid.
  • Recheck urine culture 7-14 days post-treatment to confirm clearance.

Example 3 — Large Cat Skin Infection (Maine Coon). 7 kg Maine Coon with deep pyoderma, 30 mg/kg Q12H × 21 days using 150 mg chewable.

  • Per-dose: 30 × 7 = 210 mg = 1.4 chewables → round to 1.5 (1 whole + ½ next).
  • OR: 1 × 300 mg chewable (= 300 mg, slightly over-dosed) — practical for compliance.
  • Daily total: 420 mg/day = 60 mg/kg/day (AT the cap).
  • 21-day course: 42 × 150 mg chewables OR 21 × 300 mg chewables.
  • Verify cat at healthy weight — overweight Maine Coons may have HCM (hypertrophic cardiomyopathy, common in this breed); discuss with vet.

Example 4 — Kitten — Vet Only. 1.2 kg 8-week-old kitten with skin infection.

  • Per-dose at 25 mg/kg: 30 mg = 1.2 mL of 125 mg/5 mL liquid.
  • Band: Kitten / Very Small — Vet Only.
  • Action: do NOT dose at home. Take to vet for proper assessment, accurate dispensing, and parasite check (kitten skin issues often involve fleas, ringworm, or mites alongside bacterial infection).

Example 5 — Daily Cap Exceeded Warning. 5 kg cat at 35 mg/kg Q12H (operator error in entering dose).

  • Per-dose: 35 × 5 = 175 mg.
  • Daily total: 350 mg/day = 70 mg/kg/day → EXCEEDS 60 mg/kg/day cat-specific cap.
  • The calculator flags with a red warning. Reduce dose to 25-30 mg/kg or confirm with vet that the higher dose is appropriate for severe deep infection.
  • For severe / refractory infections, alternative options (under vet supervision): cefovecin (Convenia, 8 mg/kg SC injection q14d — 14-day half-life), amoxicillin-clavulanate (Clavamox 12.5-25 mg/kg PO Q12H), or culture-guided alternatives.

Who Should Use the Cephalexin for Cats Dosage Calculator?

1
Cat Owners Verifying a Vet Prescription: Cross-check that the dispensed dose is in the standard 22-30 mg/kg Q12H range. Ask the vet to confirm if the calculator shows a value far outside the range.
2
Vet Techs and Veterinary Nurses: Quickly compute and dispense cephalexin for cats in tablet, chewable, or liquid form. Verify per-dose mg matches the prescribing veterinarian's order.
3
Multi-Cat Households: Each cat at a different size needs an individual dose calculation. Cats are NOT interchangeable for medication dosing.
4
Cat Bite / Abscess Cases: Standard first-line antibiotic for outdoor-cat fight wounds (the most common feline infection scenario). Calculator gives the dose immediately while waiting for vet appointment.
5
Breed Rescue Volunteers / Foster Carers: Manage antibiotic courses for rescued cats with abscesses, skin conditions, or post-spay/neuter prophylaxis.
6
Pet-Sitters and Boarding Kennels: Confirm the dose written on the pill bottle matches the calculator — typos and rounding errors on pharmacy labels are surprisingly common.
7
Veterinary Students and CE: Educational tool for understanding cat-specific weight-based antibiotic dosing and the dose / form / size relationship.

Technical Reference

Cephalexin Pharmacology in Cats. First-generation cephalosporin (β-lactam class), bactericidal via inhibition of bacterial cell-wall synthesis. Time-dependent killing — efficacy depends on time blood concentration stays above the MIC (T > MIC), which is why Q12H dosing is used (vs. concentration-dependent antibiotics like aminoglycosides where one large daily dose works). Cat half-life is similar to dogs (~1-2 hours) and the therapeutic window is well-established.

Pharmacokinetics in Cats:

  • Oral bioavailability: 70-85% in cats — slightly lower than dogs (75-90%) but still excellent.
  • Peak plasma concentration (Cmax): 1-2 hours post-oral dose.
  • Half-life (t½): 1-2 hours in healthy cats; prolonged in CKD.
  • Distribution: excellent into skin, soft tissue, urinary tract, bone, synovial fluid; poor CNS penetration.
  • Plasma protein binding: ~12% — minimal.
  • Excretion: 80-90% renal as unchanged drug; extend dosing interval to Q24H in cats with significant CKD (creatinine > 2.5 mg/dL).
  • Effect of food: AUC similar with or without food; food significantly reduces vomiting in cats.

Spectrum of Activity (Cat-Specific):

  • Excellent activity: Staphylococcus pseudintermedius (methicillin-susceptible) — > 80% of cat pyoderma; Streptococcus canis; Pasteurella multocida — DOMINANT bacterium in cat-bite wounds (cats and humans bitten by cats); methicillin-susceptible Staph aureus.
  • Moderate activity: susceptible E. coli, Proteus mirabilis, Klebsiella pneumoniae.
  • POOR / NO activity: Methicillin-resistant Staph (MRSP, MRSA), Enterococcus, Pseudomonas aeruginosa, anaerobes (Bacteroides, Fusobacterium — important in deep cat-bite abscesses), Mycoplasma, atypical pathogens, all fungi (Microsporum canis = ringworm — common in cats; cephalexin useless).

Standard Veterinary Indications and Course Lengths (Cat):

  • Cat-bite abscesses (most common feline infection): 22-25 mg/kg PO Q12H × 7-10 days. Vet must lance and flush abscess — antibiotic alone is inadequate for closed pus pockets. Continue 3-5 days past clinical resolution.
  • Superficial pyoderma: 22-25 mg/kg PO Q12H × 14-21 days, continue 7 days past clinical resolution.
  • Deep pyoderma: 25-30 mg/kg PO Q12H × 21-42+ days, continue 14 days past clinical resolution.
  • Uncomplicated UTI: 22-25 mg/kg PO Q12H × 7-14 days; recheck urinalysis + culture 7-14 days post-treatment.
  • Complicated UTI / pyelonephritis: 25-30 mg/kg PO Q12H × 4-6 weeks.
  • Wound and soft-tissue infections: 22-25 mg/kg PO Q12H × 7-14 days.
  • Surgical prophylaxis: 22 mg/kg IV pre-op single dose; PO course only if continued infection risk.

Adverse Effects (Incidence at Standard Doses):

  • Common (10-20%): mild GI upset — vomiting, soft stool, decreased appetite. More common in cats than dogs. Reduce by giving with a small treat or food.
  • Uncommon (3-7%): diarrhoea (sometimes from C. difficile overgrowth in long courses), allergic skin reactions (rash, urticaria). Hypersalivation from bitter taste in some liquid formulations.
  • Rare (<1%): anaphylaxis (Type I hypersensitivity, especially in cats with known beta-lactam allergy), hepatotoxicity (rare but reported in long courses), neutropenia (very rare), Stevens-Johnson syndrome (extremely rare).
  • Beta-lactam cross-reactivity: cats with documented penicillin allergy have ~10% chance of reacting to cephalexin. Use with caution; switch to a non-beta-lactam (clindamycin, doxycycline) if any prior allergic reaction.

Drug Interactions:

  • Aminoglycosides (gentamicin, amikacin): additive nephrotoxicity; avoid concurrent use.
  • Probenecid: blocks renal excretion of cephalexin, prolongs half-life. Rarely prescribed in feline medicine.
  • Antacids (calcium carbonate, magnesium hydroxide, aluminium hydroxide): reduce cephalexin absorption — separate doses by ≥ 2 hours.
  • Loop diuretics (furosemide): additive nephrotoxicity at high doses; monitor renal function in cats with concurrent CKD.
  • Live oral vaccines: cephalexin may interfere with vaccine efficacy — separate by 7-14 days.

Cat-Specific Considerations.

  • Pasteurella multocida is the dominant bacterium in cat-bite wounds — both cats biting cats and cats biting humans. Cephalexin has excellent activity against Pasteurella; this is why it's a first-line choice for cat-bite abscesses.
  • Anaerobes (Bacteroides, Fusobacterium) are also common in deep cat-bite wounds — cephalexin has POOR activity against anaerobes. For deep / chronic / non-responding abscesses, vet may add metronidazole (10-15 mg/kg PO Q12H) or switch to amoxicillin-clavulanate (Clavamox) which has anaerobic coverage.
  • Cat skin infections may be primary (true bacterial pyoderma) or secondary to underlying allergic skin disease, ectoparasites (fleas, mites), or fungal infections (ringworm). Cephalexin treats only the bacterial component — underlying causes must be addressed for lasting resolution.
  • Cats hide illness well — symptoms may be subtle (decreased grooming, hiding, reduced appetite) before infection becomes obvious. Routine veterinary check-ups catch issues early.

Alternative Antibiotics When Cephalexin Doesn't Work:

  • Amoxicillin-clavulanate (Clavamox): 12.5-25 mg/kg PO Q12H. Broader spectrum including anaerobes; good first-choice alternative for deep cat-bite wounds.
  • Cefovecin (Convenia): 8 mg/kg SC injection q14d. Long-acting injection — useful for fractious cats or owners who can't pill. 14-day half-life.
  • Doxycycline: 5-10 mg/kg PO Q12H. For mycoplasma, chlamydia, MRSP, atypical infections. Always give with water (cats can develop oesophageal strictures from dry tablets).
  • Clindamycin: 5-11 mg/kg PO Q12H. Good for anaerobic / dental infections; alternative for beta-lactam-allergic cats.
  • Marbofloxacin / pradofloxacin: fluoroquinolones; reserve for culture-proven resistant infections only (avoid blanket use to prevent resistance development). Pradofloxacin is veterinary-specific and approved for cats.
  • Metronidazole: 10-15 mg/kg PO Q12H. Anaerobic coverage; combine with cephalexin for deep cat-bite wounds.

Pregnancy and Lactation Safety in Cats. FDA Pregnancy Category B — no demonstrated fetal harm in animal studies, no adequate controlled studies in cats. Generally considered safe during feline pregnancy and lactation. Crosses placenta and is excreted in milk in low concentrations; nursing kittens typically tolerate maternal cephalexin without adverse effects. Always confirm with your veterinarian before starting any medication in pregnant or lactating queens.

Key Takeaways

Cephalexin is the standard first-line oral antibiotic for cat skin infections, abscesses, UTIs, and soft-tissue infections. Cat-specific Plumb's standard: 22-30 mg/kg PO Q12H (default 25 mg/kg), with a daily cap of 60 mg/kg/day (more conservative than the 90 mg/kg/day dog cap). The math is simple: per-dose mg = dose × weight; per-dose mL or tablets = mg / drug strength; daily total = per-dose × 2. Available in 6 cat-appropriate forms: 250 mg tablets (cheapest, often too large), 75 / 150 / 300 mg flavoured chewables (Rilexine — best fit for most cats), and 125 or 250 mg/5 mL oral suspension liquid (BEST option for very small cats). Best drug form for cats: liquid (125 mg/5 mL = 25 mg/mL) — exact mL dosing with an oral syringe; 1 mL per 5 kg of cat at 25 mg/kg. Excellent activity against Staphylococcus pseudintermedius (cat pyoderma), Pasteurella multocida (cat-bite abscesses), and susceptible Streptococcus / E. coli. ZERO activity against MRSP, MRSA, Pseudomonas, anaerobes, mycoplasma, or fungal infections — culture-and-sensitivity test if no improvement in 5-7 days. Critical safety: prescription only — always confirm dose with vet. Complete the full course (7-21 days for skin / abscess, 7-14 days for UTI) even if symptoms resolve early.

Frequently Asked Questions

What is the Cephalexin for Cats Dosage Calculator?
It implements the cat-specific Plumb's Veterinary Drug Handbook cephalexin dose: 22-30 mg/kg PO every 12 hours (default 25 mg/kg Q12H), with daily cap of 60 mg/kg/day in cats (more conservative than the dog cap of 90 mg/kg/day). Enter your cat's weight, customise dose strength if needed, pick from 6 cat-appropriate commercial formulations (250 mg tablets, 75 / 150 / 300 mg chewables, 125 or 250 mg/5 mL liquid), and instantly get the per-dose mg, exact mL or tablet count, daily total, and 5-band size classification.

Designed for cat owners verifying a vet prescription, vet techs preparing dispensed medication, multi-cat households, and emergency-clinic phone triage.

Pro Tip: Pair this with our Cephalexin for Dogs Dosage Calculator for the canine equivalent in multi-pet households.

What's the cat dose of cephalexin?
22-30 mg/kg PO every 12 hours per Plumb's Veterinary Drug Handbook. Default 25 mg/kg Q12H — the conservative middle of the range. Maximum daily total: 60 mg/kg/day (cat-specific cap, more conservative than dogs). For a typical 4 kg cat at 25 mg/kg: per-dose 100 mg = 4 mL of 125 mg/5 mL liquid; daily total 200 mg = 8 mL liquid per day. Course length: 7-10 days for cat-bite abscesses; 14-21 days for superficial pyoderma; 21-42 days for deep pyoderma; 7-14 days for uncomplicated UTI.
What is cephalexin used for in cats?
First-line antibiotic for: (1) Cat-bite abscesses (the MOST common feline infection — outdoor cats fighting; cephalexin has excellent activity against Pasteurella multocida, the dominant bacterium in cat-bite wounds). (2) Superficial and deep pyoderma (skin infections, often secondary to allergies). (3) Hot spots (acute moist dermatitis). (4) Urinary tract infections caused by susceptible E. coli, Proteus, or Staph. (5) Wound and soft-tissue infections. (6) Post-surgical prophylaxis. NOT effective against Pseudomonas, anaerobes, mycoplasma, or methicillin-resistant Staph (MRSP) — culture-and-sensitivity test if no improvement in 5-7 days.
What forms of cephalexin are best for cats?
Liquid (125 mg/5 mL = 25 mg/mL) is the BEST option for most cats — exact mL dosing with an oral syringe; 1 mL per 5 kg of cat at 25 mg/kg. Cherry or chicken flavoured; most cats tolerate the taste. Chewables (75 / 150 / 300 mg, Rilexine brand): also excellent — flavoured tablets, easier than pills, no pill-pocket needed; choose strength matching the per-dose mg. 250 mg tablets: usually too large for typical cats (a 4 kg cat needs only 100 mg = 2/5 of a tablet), only practical for medium-large cats with halving / quartering. The 500 mg dog tablets and 600 mg dog chewables are excluded from the calculator — too large for cat-sized doses.
How much liquid cephalexin for a cat?
Children's liquid cephalexin (125 mg/5 mL = 25 mg/mL) at the standard 25 mg/kg dose: 1 mL per 1 kg of cat body weight per dose, every 12 hours. Quick reference: 2 kg cat = 2 mL; 3 kg = 3 mL; 4 kg = 4 mL; 5 kg = 5 mL; 6 kg = 6 mL; 7 kg = 7 mL. Use a 5 mL oral syringe (NOT a kitchen teaspoon) for accuracy. For 250 mg/5 mL liquid (50 mg/mL), halve these volumes (1 mL per 2 kg).
How long should the course of cephalexin last?
Course depends on infection: Cat-bite abscess (most common): 7-10 days, continuing 3-5 days past clinical resolution. Vet must lance and flush abscess first — antibiotic alone is inadequate for closed pus pockets. Superficial pyoderma: 14-21 days, continue 7 days past resolution. Deep pyoderma: 21-42+ days, continue 14 days past resolution. Uncomplicated UTI: 7-14 days; recheck urine culture 7-14 days post-treatment to confirm clearance. Complicated UTI / pyelonephritis: 4-6 weeks. NEVER stop early just because symptoms resolve — bacteria remain present at sub-symptomatic levels and stopping early is the #1 cause of antibiotic resistance and recurrent infection.
What if my cat vomits after taking cephalexin?
Mild GI upset (vomiting, soft stool, decreased appetite) occurs in 10-20% of cats on cephalexin — slightly more common than in dogs. If vomiting within 30 minutes of dosing and the dose is visibly returned: repeat with food. If vomiting later: dose was likely absorbed, skip the missed dose, resume at next scheduled time (do NOT double-dose). For persistent vomiting: (1) ensure dosing with food / treat; (2) add famotidine (Pepcid AC) 0.5-1 mg/kg PO Q24H; (3) split the dose; (4) switch to a different antibiotic (clindamycin, doxycycline, or cefovecin Convenia injection if oral dosing is the problem). Severe vomiting + diarrhoea + lethargy = vet visit (could indicate Clostridium difficile overgrowth or allergic reaction).
Can my cat be allergic to cephalexin?
Yes — allergic reactions occur in < 1% of cats but can be serious. Mild signs: skin rash, hives, facial swelling, mild itch — discontinue and call vet. Severe signs: facial / throat swelling, difficulty breathing, collapse — EMERGENCY, go directly to vet immediately. Cats with documented penicillin allergy have ~10% chance of cross-reactivity to cephalexin (both are beta-lactams) — use with caution and have your vet confirm the previous reaction was true allergy (not just GI upset). Switch to a non-beta-lactam (clindamycin, doxycycline) if any prior beta-lactam allergic reaction.
Can I use leftover dog cephalexin for my cat?
Cephalexin is the SAME drug in cat and dog formulations — same active ingredient, same per-mg potency. BUT: (1) the dose is different (cats 22-30 mg/kg vs dogs 22-30 mg/kg — same range BUT cats have a stricter daily cap of 60 mg/kg/day vs dogs at 90 mg/kg/day); (2) the strength may be wrong (500 mg dog tablets and 600 mg dog chewables are too large for cats and impractical to split accurately); (3) NEVER use without veterinary confirmation — the vet needs to confirm the diagnosis (culture, urinalysis), set the dose, and confirm the course length. Veterinary cephalexin (Rilexine flavoured chewables) is more palatable and easier to administer for cats than dog formulations.
What if cephalexin isn't working?
If your cat's infection hasn't improved within 5-7 days at the correct dose, see your vet for culture-and-sensitivity testing. Common causes of treatment failure: (1) Methicillin-resistant Staphylococcus pseudintermedius (MRSP) — emerging resistance threat; affects 5-15% of cat skin infections in some regions. (2) Pseudomonas, anaerobes, or mycoplasma — cephalexin has zero or poor activity against these. (3) Underlying cause not addressed — allergic atopy, ectoparasites (fleas, mites), ringworm (fungal — cephalexin useless), foreign body. (4) Inadequate dose / course length. (5) Poor compliance — pilling cats is hard; verify cat actually swallowed each dose. Alternatives based on culture results: doxycycline (mycoplasma, MRSP), amoxicillin-clavulanate (anaerobic coverage), cefovecin Convenia injection (long-acting alternative for fractious cats), or fluoroquinolones (only if culture-confirmed susceptible).
Is cephalexin safe in pregnancy for cats?
FDA Pregnancy Category B — no demonstrated fetal harm in animal studies, no adequate controlled studies in cats. Generally considered safe during feline pregnancy and lactation, and is one of the antibiotics of choice for breeding queens with confirmed bacterial infection. Crosses the placenta and is excreted in milk in low concentrations; nursing kittens typically tolerate maternal cephalexin without adverse effects. Always confirm with your veterinarian before starting any medication during pregnancy or lactation. Avoid in late pregnancy (last week) only if there's specific concern; otherwise standard dosing applies.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our ToolsACE veterinary team built this calculator on the cat-specific Plumb's Veterinary Drug Handbook cephalexin dose (22-30 mg/kg PO Q12H, default 25 mg/kg), cross-referenced with the ACVIM antimicrobial use guidelines and the ISCAID pyoderma consensus. Cephalexin is a first-generation cephalosporin (β-lactam class) widely used in cats for skin and soft-tissue infections, abscesses, urinary tract infections, and post-surgical prophylaxis. The calculator covers 6 cat-appropriate commercial formulations: 250 mg tablets (often too large for typical cats — usually halved or quartered), 75 / 150 / 300 mg flavoured chewables (best fit for most cats), and 125 or 250 mg / 5 mL oral suspension liquid (BEST option for small cats and exact sub-tablet dosing). The 500 mg dog-dose tablets and 600 mg chewables are excluded — these are impractical for cat-sized doses. Per-dose mg, units (tablets / chewables / mL) per dose, daily total, daily mg/kg ratio (capped at 60 mg/kg/day in cats), and a 5-band size classification are computed in one pass alongside an 8-breed reference table.

Plumb's Veterinary Drug Handbook (10th ed.)ACVIM Antimicrobial GuidelinesISCAID Pyoderma Consensus

Disclaimer

Estimates only — always consult your veterinarian before giving cephalexin or any prescription medication to your cat. Cephalexin is a Rx-only veterinary antibiotic; standard cat dose range is 22-30 mg/kg every 12 hours, with daily cap 60 mg/kg/day (more conservative than the 90 mg/kg/day dog cap). Exact dose, frequency, and course length must be set by your vet based on infection type, severity, bacterial sensitivity, kidney function, pregnancy / lactation status, and concurrent medications. Complete the full prescribed course (typically 7-21 days for skin / abscess, 7-14 days for UTI) even if symptoms resolve early. Cephalexin is NOT effective against Pseudomonas, anaerobes, mycoplasma, or methicillin-resistant Staphylococci. For severe allergic reactions, seek emergency veterinary care immediately. Source data: Plumb's Veterinary Drug Handbook (10th ed., 2023), ACVIM Antimicrobial Use Guidelines (2017), ISCAID Pyoderma Consensus.