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Cephalexin for Dogs Dosage Calculator

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Plumb's Veterinary Standard.
8 Drug Forms.
13 Reference Breeds.
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How it Works

01Enter Dog Weight

Use current body weight from a recent vet visit (kg, lb, g, or oz). Cephalexin scales linearly with weight.

02Set Dose & Frequency

Default 25 mg/kg (range 22-30) every 12 hours. Q8H for severe infections; daily cap 90 mg/kg.

03Pick Drug Form

8 forms: 250 / 500 mg tablets, 75 / 150 / 300 / 600 mg chewables, 125 or 250 mg/5 mL liquid.

04Get mg + Units / Dose

Per-dose mg, tablets/chewables/mL per dose, daily total, and 13-breed dose-reference table.

What is a Cephalexin for Dogs Dosage Calculator?

Cephalexin (brand names Keflex in human medicine, Rilexine in veterinary medicine) is the most commonly prescribed first-line antibiotic for canine pyoderma — the bacterial skin infection that is by far the most common reason a dog owner ends up at the vet for an antibiotic prescription. Our Cephalexin for Dogs Dosage Calculator implements the standard Plumb's Veterinary Drug Handbook dose: 22-30 mg/kg every 8-12 hours, with default 25 mg/kg Q12H. Enter your dog's body weight, pick from 8 commercial formulations (250 or 500 mg tablets, 75 / 150 / 300 / 600 mg flavoured Rilexine chewables, 125 or 250 mg/5 mL liquid suspension), and instantly get the per-dose mg, units (tablets / chewables / mL) per dose, daily total in both mg and mg/kg, with a 5-band size classification (toy / puppy → small → medium → large → giant) and a 13-breed reference table to sanity-check the result.

Cephalexin is a first-generation cephalosporin (β-lactam class) that is highly active against Staphylococcus pseudintermedius — the dominant skin pathogen in dogs, responsible for over 90% of superficial and deep pyoderma cases. It is well absorbed orally (taken with food to reduce GI upset), achieves excellent skin / soft-tissue concentrations, and has an outstanding safety profile across decades of clinical use. Common veterinary indications include superficial pyoderma (impetigo, folliculitis), deep pyoderma (furunculosis, callus pyoderma, German Shepherd pyoderma), hot spots (acute moist dermatitis), urinary tract infections (UTI) caused by susceptible bacteria, wound and soft-tissue infections, and post-surgical prophylaxis.

Designed for dog owners trying to verify a veterinary prescription, vet techs and nurses preparing dispensed medication, breed-club rescue volunteers handling Rx admin, and any pet owner who lost the dosing instructions on the bottle, the tool runs entirely in your browser — no account, no data stored. Critical caveat: cephalexin is a prescription antibiotic — this calculator does NOT replace a veterinary diagnosis. Always confirm dose, frequency, and course length with your veterinarian; complete the full prescribed course (typically 10-14 days for pyoderma, 7-14 days for UTI) even if symptoms resolve early; and culture-and-sensitivity test if there's no improvement in 5-7 days, since methicillin-resistant Staphylococcus pseudintermedius (MRSP) and MRSA require entirely different antibiotics.

Pro Tip: Pair this with our Benadryl Dosage for Dogs Calculator for managing pyoderma-associated allergic itch, our Dog Pregnancy Calculator for breeding queens, or our Raw Dog Food Calculator for nutrition support during recovery.

How to Use the Cephalexin for Dogs Dosage Calculator?

Enter Your Dog's Current Weight: Use weight from a recent vet visit, or weigh on a kitchen / pet scale. Cephalexin dose scales linearly with body weight, so an inaccurate weight directly translates to an inaccurate dose. Use ACTUAL body weight, not ideal weight (lean-body-mass dosing is for chemotherapy / NSAID protocols, not for antibiotics).
Set the Dose Strength (default 25 mg/kg): Plumb's standard range is 22-30 mg/kg per administration (≈ 10-15 mg/lb). 22-25 mg/kg is typical for superficial pyoderma and uncomplicated UTI; 30 mg/kg is reserved for severe deep pyoderma and resistant infections. NEVER exceed 30 mg/kg per single dose, and NEVER exceed 90 mg/kg/day total.
Pick Frequency — Q12H or Q8H: Q12H (every 12 hours, BID, twice daily) is standard for skin infections and uncomplicated UTI — easier compliance for owners. Q8H (every 8 hours, TID, three times daily) is used for severe infections, deep pyoderma, and pyoderma in immunosuppressed dogs (Cushing's, diabetes mellitus, allergic atopy on cyclosporin).
Pick the Drug Form: 8 commercial formulations covered. Tablets (250 or 500 mg): cheapest generic option, typically scored for halving. Flavoured chewables (Rilexine 75 / 150 / 300 / 600 mg): easier to dose, no pill-pocket needed, but more expensive. Oral suspension liquid (125 or 250 mg per 5 mL): best for small dogs, puppies, and any dog where exact sub-tablet dosing is needed.
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 frequency for daily total, and divides daily mg by weight kg for the daily mg/kg/day ratio.
Read the Result + Daily Dosage: Per-dose mg, units per dose, daily total mg, daily mg/kg/day (compare to 90 mg/kg/day cap). Use the 13-breed reference table to sanity-check against typical doses for similar-sized dogs. Complete the full prescribed course — stopping early is the #1 cause of antibiotic resistance.
Give With Food: Cephalexin GI absorption is similar with or without food, but giving with a small meal significantly reduces vomiting and gastric upset (especially in toy breeds and brachycephalic dogs). NOT antacids though — separate antacid administration by 2 hours before or after the cephalexin dose.

How is the cephalexin dose calculated?

Cephalexin dosing in dogs is the simplest possible weight-based pharmacology — multiply mg/kg by body weight in kg to get mg per dose, then divide by tablet/chewable strength or by mg/mL of liquid to get units per dose. The mathematics is identical to amoxicillin, clavamox, doxycycline, and most other oral antibiotics; the dose number changes but the formula is the same.

Standard veterinary range from Plumb's Veterinary Drug Handbook (10th ed., 2023), cross-referenced with the ACVIM Antimicrobial Use Guidelines (2017) and the ISCAID Canine Pyoderma Consensus (2014, updated 2020).

Core Formula

For a dog of weight W (kg) at dose strength D (mg/kg) given F times per day:

Per-dose mg = D × W

Per-dose tablets = (D × W) / tablet_strength_mg

Per-dose mL (liquid) = (D × W) / liquid_concentration_mg_per_mL

Daily total mg = D × W × F

Standard Veterinary Dose Range

  • Superficial pyoderma / uncomplicated UTI: 22-25 mg/kg PO Q12H × 14-21 days.
  • Deep pyoderma / severe infections: 25-30 mg/kg PO Q12H or Q8H × 28-42+ days (until 2 weeks past clinical resolution).
  • Acute moist dermatitis (hot spots) when systemic Rx needed: 22-25 mg/kg PO Q12H × 7-14 days.
  • Wound infections / soft tissue: 22-25 mg/kg PO Q12H × 7-14 days, longer if osteomyelitis suspected.
  • Post-surgical prophylaxis: 22 mg/kg single pre-op dose IV; oral course only if continued infection risk.
  • Maximum daily total: ≤ 90 mg/kg/day across all doses.

Commercial Formulations and Strengths

  • Tablets, 250 mg: generic — cheapest option. Often scored.
  • Tablets, 500 mg: generic — for medium-large dogs. Often scored.
  • Flavoured chewables (Rilexine), 75 mg: for toy and small breeds.
  • Flavoured chewables (Rilexine), 150 mg: for small-medium dogs.
  • Flavoured chewables (Rilexine), 300 mg: for medium dogs.
  • Flavoured chewables (Rilexine), 600 mg: for large dogs.
  • Oral suspension, 125 mg / 5 mL (= 25 mg/mL): for very small dogs, puppies, dogs that won't take pills.
  • Oral suspension, 250 mg / 5 mL (= 50 mg/mL): for small-medium dogs needing liquid dosing.

Worked Example — 25 kg Mid-Size Dog

A 25 kg Border Collie with superficial pyoderma, 25 mg/kg Q12H × 21 days using 500 mg tablets:

  • Per-dose: 25 × 25 = 625 mg.
  • Tablets per dose: 625 / 500 = 1.25 tablets — round to 1.5 (1 whole + 1 half) for practical dispensing.
  • Daily total: 625 × 2 = 1,250 mg.
  • Daily mg/kg: 50 mg/kg/day (well below 90 mg/kg/day cap).
  • 21-day course total: 1,250 × 21 = 26,250 mg ≈ 53 × 500 mg tablets dispensed.

Why Cephalexin is the First-Line Choice

  • Targeted spectrum: excellent activity against Staphylococcus pseudintermedius (the dominant canine skin pathogen — over 90% of pyoderma cases) without unnecessarily broad coverage that drives resistance.
  • Bactericidal: kills bacteria rather than just slowing growth, which clears infections faster.
  • Excellent skin penetration: achieves therapeutic concentrations at the site of infection.
  • Outstanding safety: decades of clinical use; minimal toxicity at standard doses; safe in pregnancy (FDA Category B).
  • Inexpensive: generic 500 mg tablets cost < $0.20 per tablet from compounding pharmacies.
  • Twice-daily compliance: Q12H is owner-friendly; missed doses are uncommon.

When Cephalexin DOES NOT Work

  • Methicillin-resistant Staphylococcus pseudintermedius (MRSP): the major emerging threat in canine dermatology — cephalexin has zero activity. Requires culture-and-sensitivity testing and entirely different antibiotics (often doxycycline, chloramphenicol, or fluoroquinolones based on the antibiogram).
  • MRSA (methicillin-resistant Staph aureus): less common in dogs than MRSP but a public-health concern; cephalexin ineffective.
  • Pseudomonas aeruginosa: common in chronic otitis externa, deep wound infections; cephalexin completely ineffective.
  • Anaerobes: poor activity; bite-wound infections often need additional metronidazole or clindamycin coverage.
  • Atypical pathogens (Mycoplasma, Mycobacterium): cephalexin ineffective.
  • Fungal / yeast infections: cephalexin is an ANTIBIOTIC — useless against Malassezia, dermatophytes, or any fungal pathogen.
Real-World Example

Cephalexin for Dogs Dosage – Worked Examples

Example 1 — Small Dog Pyoderma (Yorkshire Terrier). 3 kg Yorkie with superficial pyoderma, 25 mg/kg Q12H × 14 days using 75 mg chewables.
  • Per-dose: 25 × 3 = 75 mg per dose = exactly 1× 75 mg chewable.
  • Daily total: 75 × 2 = 150 mg/day.
  • Daily mg/kg: 50 mg/kg/day (within range).
  • 14-day course: 28 × 75 mg chewables dispensed.
  • Cost: ~$25-$40 for the full course (Rilexine retail).

Example 2 — Medium Dog UTI (Labrador). 30 kg Lab with culture-confirmed E. coli UTI (sensitive to cephalexin), 22 mg/kg Q12H × 14 days using 500 mg tablets.

  • Per-dose: 22 × 30 = 660 mg per dose ≈ 1.3 tablets — practical: round to 1.5 tablets (1 whole + 1 half) = 750 mg per dose.
  • Or use 600 mg chewable rounded to 1 chewable = 600 mg per dose (slightly under-dosed but acceptable).
  • Daily total: 1,320 mg (calculated) or 1,500 mg (rounded with half-tablet).
  • Daily mg/kg: 44-50 mg/kg/day (within range).
  • 14-day course: 42 × 500 mg tablets dispensed; recheck urine culture 7-14 days post-treatment to confirm clearance.

Example 3 — Large Dog Deep Pyoderma (German Shepherd). 35 kg GSD with deep pyoderma / furunculosis, 30 mg/kg Q12H × 42 days using 500 mg tablets.

  • Per-dose: 30 × 35 = 1,050 mg per dose ≈ 2.1 tablets — practical: round to 2 × 500 mg tablets = 1,000 mg per dose.
  • Daily total: 2,000 mg/day = 57 mg/kg/day (within 90 mg/kg/day cap).
  • 42-day course: 168 × 500 mg tablets dispensed (cost $30-$60 generic).
  • Continue 14 days past clinical resolution per ISCAID guidelines for deep pyoderma.
  • Culture-and-sensitivity test if no improvement in 7-10 days — German Shepherd pyoderma has elevated MRSP risk.

Example 4 — Toy Breed Hot Spot (Chihuahua). 2.5 kg Chihuahua with acute moist dermatitis, 25 mg/kg Q12H × 7 days using liquid 125 mg/5 mL (25 mg/mL).

  • Per-dose: 25 × 2.5 = 62.5 mg per dose.
  • Liquid mL: 62.5 / 25 = 2.5 mL per dose.
  • Daily total: 125 mg/day = 5 mL/day = 50 mg/kg/day.
  • 7-day course: 35 mL liquid dispensed (one bottle).
  • Use a 3 mL oral syringe (NOT a kitchen teaspoon) for accuracy; teaspoons vary 4-7 mL.

Example 5 — Giant Breed Wound Infection (Great Dane). 70 kg Great Dane with infected laceration, 25 mg/kg Q12H × 10 days using 500 mg tablets.

  • Per-dose: 25 × 70 = 1,750 mg per dose = 3.5 × 500 mg tablets — practical: round to 3 × 500 mg = 1,500 mg per dose.
  • Many vets cap individual cephalexin doses at 1,000-1,500 mg regardless of body weight to limit GI side effects in giant breeds.
  • Daily total: 3,000 mg/day = 43 mg/kg/day (within range).
  • 10-day course: 60 × 500 mg tablets dispensed (about $12 generic, $50+ Rilexine brand).
  • Watch for GI upset — large doses in Great Danes have higher rates of vomiting / soft stool. Give with food; consider famotidine 0.5-1 mg/kg Q24H if GI signs persist.

Who Should Use the Cephalexin for Dogs Dosage Calculator?

1
Dog 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 dose far outside the range.
2
Vet Techs and Veterinary Nurses: Quickly compute and dispense cephalexin in tablet, chewable, or liquid form at the clinic. Verify per-dose mg matches the prescribing veterinarian's order before sending home.
3
Multi-Dog Households: If only one dog is on cephalexin, calculate per-dose accurately to avoid accidentally giving it to the wrong dog (different size = different dose).
4
Breed Rescue Volunteers / Foster Carers: Manage post-intake antibiotic courses for rescued dogs with neglect-related skin conditions; standardise dosing across foster homes.
5
Pet-Sitters and Boarding Kennels: Confirm the dose written on the pill bottle matches what the calculator says — typos and rounding errors on pharmacy labels are surprisingly common.
6
Veterinary Students and CE: Educational tool for understanding weight-based antibiotic dosing and the relationship between dose / frequency / formulation strength.
7
Dog Owners with Recurrent Pyoderma Cases: Track dose escalations across recurrent infections; identify when dose has plateaued at the 30 mg/kg cap and culture-and-sensitivity testing is needed instead of higher doses.

Technical Reference

Cephalexin Pharmacology. First-generation cephalosporin (β-lactam class), bactericidal via inhibition of bacterial cell-wall synthesis (binds penicillin-binding proteins, blocks cross-linking of peptidoglycan). Time-dependent killing — efficacy depends on the time blood concentration stays above the MIC (T > MIC), which is why Q12H or Q8H dosing is needed (vs. concentration-dependent antibiotics like aminoglycosides where one large daily dose works).

Pharmacokinetics in Dogs.

  • Oral bioavailability: 75-90% — high and consistent.
  • Peak plasma concentration (Cmax): reached 1-2 hours after oral dose.
  • Half-life (t½): 1-2 hours in healthy dogs; prolonged in renal disease.
  • Distribution: excellent into skin, soft tissue, urinary tract, bone, synovial fluid; poor CNS penetration.
  • Plasma protein binding: ~12% — minimal, so most drug is bioavailable.
  • Excretion: 80-90% renal as unchanged drug; dose adjustment needed in chronic kidney disease (extend interval to Q24H if creatinine clearance is significantly reduced).
  • Effect of food: AUC similar with or without food, but food significantly reduces GI upset.

Spectrum of Activity (per VetCAST 2023):

  • Excellent activity: Staphylococcus pseudintermedius (methicillin-susceptible), Streptococcus canis, S. dysgalactiae, S. zooepidemicus, beta-hemolytic streptococci, methicillin-susceptible Staph aureus.
  • Moderate activity: Proteus mirabilis (most strains), E. coli (50-70% of canine UTI isolates), Klebsiella pneumoniae (variable).
  • POOR / NO activity: Methicillin-resistant Staphylococcus pseudintermedius (MRSP), MRSA, Enterococcus spp., Pseudomonas aeruginosa, anaerobes (most), Mycoplasma, atypical pathogens, all fungi.

Standard Veterinary Indications and Course Lengths:

  • Superficial pyoderma (impetigo, folliculitis): 22-25 mg/kg PO Q12H × 14-21 days, continue 7 days past clinical resolution.
  • Deep pyoderma (furunculosis, cellulitis): 25-30 mg/kg PO Q12H × 28-42+ days, continue 14 days past clinical resolution.
  • Acute moist dermatitis (hot spots) — when systemic Rx needed: 22-25 mg/kg PO Q12H × 7-14 days.
  • 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.
  • Osteomyelitis: 25-30 mg/kg PO Q12H × 4-8+ weeks (in conjunction with surgical debridement).
  • Surgical prophylaxis: 22 mg/kg IV pre-op single dose; PO course only if continued infection risk.

Adverse Effects (incidence at standard doses):

  • Common (5-15%): mild GI upset — vomiting, soft stool, decreased appetite. Reduce by giving with food.
  • Uncommon (1-5%): diarrhoea (sometimes from C. difficile overgrowth in long courses), allergic skin reactions (rash, urticaria).
  • Rare (<1%): anaphylaxis (Type I hypersensitivity, especially in dogs with known beta-lactam allergy), drug-induced hepatitis, blood dyscrasias (very rare), Stevens-Johnson syndrome (extremely rare).
  • Beta-lactam cross-reactivity: dogs with documented penicillin allergy have ~10% chance of also 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 — useful for severe infections, but rarely prescribed in veterinary 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.
  • Warfarin and oral anticoagulants: cephalexin may potentiate anticoagulant effect — rarely clinically significant but monitor PT/PTT in dogs on long-term anticoagulation.
  • Live oral vaccines (canine bordetella): cephalexin may interfere with vaccine efficacy — separate by 7-14 days.

MRSP Surveillance Note. Methicillin-resistant Staphylococcus pseudintermedius (MRSP) has emerged as the major antimicrobial-resistance threat in canine dermatology over the past two decades. MRSP carries the mecA gene that encodes a modified penicillin-binding protein (PBP2a) with reduced affinity for all beta-lactams — meaning cephalexin, amoxicillin-clavulanate, cefpodoxime, and all other beta-lactams are ineffective. Risk factors for MRSP: repeated antibiotic courses, hospital exposure, immunosuppression (allergic atopy on ciclosporin / oclacitinib, Cushing's disease, diabetes), German Shepherd / GSD-mix breed (some genetic predisposition). Recommendation: if a pyoderma case fails to improve in 7-10 days on appropriate cephalexin, do a culture-and-sensitivity test; if MRSP is identified, switch to a culture-guided alternative (often doxycycline 5-10 mg/kg PO Q12H, chloramphenicol 40-50 mg/kg PO Q8H, or fluoroquinolones if approved by the antibiogram).

Antibiotic Stewardship. The ISCAID and ACVIM guidelines emphasise: (1) culture-and-sensitivity test BEFORE empirical Rx for any deep, recurrent, or treatment-failed infection; (2) use the narrowest-spectrum effective antibiotic — cephalexin for susceptible Staph rather than fluoroquinolones; (3) appropriate course duration — neither too short (fosters resistance) nor too long (drives dysbiosis); (4) topical therapy (chlorhexidine shampoo / mousse, mupirocin) as adjunct or alternative to systemic Rx for superficial pyoderma; (5) recheck rather than refill — every cephalexin course should end with a recheck visit, not an automatic refill.

Pregnancy and Lactation Safety. FDA Pregnancy Category B (no demonstrated fetal harm in animal studies, no adequate human studies). Generally considered safe during canine pregnancy and lactation. Crosses placenta and is excreted in milk in low concentrations; nursing puppies typically tolerate maternal cephalexin without adverse effects. Dose-adjust for late pregnancy (increased plasma volume) only if recommended by the prescribing veterinarian.

Key Takeaways

Cephalexin is the standard first-line oral antibiotic for canine pyoderma — the most common bacterial infection in dogs. Standard veterinary dose: 22-30 mg/kg every 8-12 hours (default 25 mg/kg Q12H). The math is simple: per-dose mg = dose × weight; per-dose tablets = mg / tablet strength; daily total = per-dose × frequency. Available in 8 commercial formulations: 250 / 500 mg tablets (cheapest), Rilexine flavoured chewables (75 / 150 / 300 / 600 mg), and 125 or 250 mg/5 mL oral suspension (best for small dogs and puppies). Daily cap: ≤ 90 mg/kg/day across all doses. Excellent activity against Staphylococcus pseudintermedius (90% of canine pyoderma); ZERO activity against MRSP, MRSA, Pseudomonas, anaerobes, or fungal infections — culture-and-sensitivity test if no improvement in 5-7 days. Critical safety: prescription only — always confirm dose with your veterinarian. Complete the full course (10-14 days for pyoderma, 7-14 days for UTI) even if symptoms resolve early. Give with food to reduce GI upset. Avoid co-administration with aminoglycosides (additive nephrotoxicity); separate from antacids by 2 hours.

Frequently Asked Questions

What is the Cephalexin for Dogs Dosage Calculator?
It implements the standard Plumb's Veterinary Drug Handbook cephalexin dose for dogs: 22-30 mg/kg every 8-12 hours (default 25 mg/kg Q12H). Enter your dog's body weight, pick from 8 commercial formulations (250 / 500 mg tablets, 75 / 150 / 300 / 600 mg Rilexine chewables, 125 or 250 mg/5 mL liquid suspension), and instantly get the per-dose mg, units (tablets / chewables / mL) per dose, daily total in mg and mg/kg, plus a 5-band size classification and 13-breed reference table.

Designed for dog owners verifying a vet prescription, vet techs preparing dispensed medication, breed-rescue volunteers, and any pet owner who lost the dosing instructions on the bottle.

Pro Tip: Pair this with our Benadryl Dosage for Dogs Calculator for managing pyoderma-associated allergic itch.

What's the standard cephalexin dose for dogs?
22-30 mg/kg PO every 8-12 hours per Plumb's Veterinary Drug Handbook and ACVIM antimicrobial guidelines. Default 25 mg/kg every 12 hours (BID) for most uncomplicated skin and UTI infections. Use 30 mg/kg every 8-12 hours for severe deep pyoderma. Maximum daily total: 90 mg/kg/day across all doses. In imperial units: 10-15 mg per pound. Course length: typically 14-21 days for superficial pyoderma, 28-42+ days for deep pyoderma, 7-14 days for uncomplicated UTI.
What is cephalexin used for in dogs?
Cephalexin (Keflex / Rilexine) is the standard first-line oral antibiotic for: (1) superficial pyoderma (impetigo, folliculitis) — the most common indication; (2) deep pyoderma (furunculosis, cellulitis); (3) hot spots (acute moist dermatitis) when systemic Rx is needed; (4) urinary tract infections (UTI) caused by susceptible E. coli, Proteus, Staph; (5) wound and soft-tissue infections; (6) osteomyelitis (in conjunction with surgical debridement); (7) post-surgical prophylaxis. It works because over 90% of canine skin infections are caused by Staphylococcus pseudintermedius, and cephalexin has excellent activity against this pathogen.
What forms does cephalexin come in?
8 common commercial formulations: Generic tablets, 250 mg and 500 mg (cheapest — typically scored for halving). Rilexine flavoured chewables, 75 / 150 / 300 / 600 mg (easier to administer, more expensive — manufactured specifically for veterinary use). Oral suspension liquid, 125 mg/5 mL (= 25 mg/mL) and 250 mg/5 mL (= 50 mg/mL) (best for small dogs, puppies, and any dog where exact sub-tablet dosing is needed). The calculator handles all 8 forms — pick whichever your vet has dispensed.
Should I give cephalexin with food?
Yes, give with a small meal. Cephalexin GI absorption is similar with or without food (no clinically significant change in AUC or Cmax), but giving with food significantly reduces vomiting and gastric upset, especially in toy breeds, brachycephalic dogs, and elderly dogs. Exception: do NOT give with antacids (calcium carbonate, magnesium hydroxide, aluminium hydroxide) — antacids reduce cephalexin absorption. Separate antacid administration by ≥ 2 hours before or after the cephalexin dose.
How long should the course of cephalexin last?
Course length depends on the infection: Superficial pyoderma (most common): 14-21 days, continue 7 days past clinical resolution. Deep pyoderma (furunculosis): 28-42+ days, continue 14 days past clinical resolution. Hot spots: 7-14 days. Uncomplicated UTI: 7-14 days; recheck urine culture 7-14 days post-treatment. Complicated UTI / pyelonephritis: 4-6 weeks. Osteomyelitis: 4-8+ weeks. NEVER stop early just because symptoms resolve — the bacteria remain present at sub-symptomatic levels and stopping early is the #1 cause of antibiotic resistance and recurrent infection.
What if my dog vomits after taking cephalexin?
If vomiting occurs within 30 minutes of dosing and the pill / tablet is visibly returned, repeat the dose with food. If vomiting is later than 30 minutes, the dose was likely absorbed — skip the missed dose and resume at the next scheduled time (do NOT double-dose). For persistent vomiting (more than 1-2 episodes per day), contact your vet — options include: (1) ensure dosing with food; (2) add famotidine (Pepcid AC) 0.5-1 mg/kg PO Q24H; (3) split the dose (give half tablet morning, half evening, etc.); (4) switch to a different antibiotic (clindamycin, doxycycline) if vomiting is severe. Profuse vomiting + diarrhoea + lethargy can indicate Clostridium difficile overgrowth — vet visit needed.
Can my dog be allergic to cephalexin?
Yes — cephalexin allergic reactions occur in < 1% of dogs but can be serious. Mild signs: skin rash, hives (urticaria), facial swelling, mild itch — discontinue and call vet. Severe signs: facial / throat swelling, difficulty breathing, collapse — EMERGENCY, go directly to vet immediately (anaphylaxis). Dogs with documented penicillin allergy have ~10% chance of cross-reactivity to cephalexin — 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 give my dog human cephalexin (Keflex)?
Cephalexin is the same drug in human (Keflex) and veterinary (Rilexine) formulations — same active ingredient, same dose-per-mg. BUT never use leftover human cephalexin without veterinary confirmation: (1) the vet needs to confirm the diagnosis (skin culture, urinalysis, etc.); (2) the vet needs to set the dose, frequency, and course length; (3) human capsules / tablets may have inactive ingredients (e.g. xylitol in some chewables) that are toxic to dogs — verify the formulation. Veterinary cephalexin (Rilexine flavoured chewables) is more palatable and easier to administer; generic human-formulation cephalexin tablets are cheaper for large dogs. Either way, the dose and course must be set by your vet.
What if cephalexin isn't working?
If your dog's pyoderma or UTI hasn't improved within 5-7 days of starting cephalexin at the correct dose, do not just "keep going" — see your vet for a culture-and-sensitivity test. The most likely cause is methicillin-resistant Staphylococcus pseudintermedius (MRSP) — an emerging resistance threat that affects an estimated 10-20% of canine pyoderma cases in some regions. MRSP is genetically resistant to ALL beta-lactams (cephalexin, amoxicillin-clavulanate, cefpodoxime, etc.) and requires entirely different antibiotics (often doxycycline, chloramphenicol, or fluoroquinolones based on the antibiogram). Other causes of treatment failure: (1) wrong diagnosis (fungal infection, demodex, atopy mimicking pyoderma); (2) underlying cause not addressed (allergic atopy, hypothyroidism, Cushing's); (3) inadequate dose or course length; (4) poor owner compliance.
Is cephalexin safe in pregnancy?
FDA Pregnancy Category B — no demonstrated fetal harm in animal studies, no adequate controlled human studies. Cephalexin is generally considered safe during canine pregnancy and lactation, and is one of the antibiotics of choice for breeding bitches with confirmed bacterial infection. Crosses the placenta and is excreted in milk in low concentrations; nursing puppies 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 is concern about reaching therapeutic concentration; otherwise standard dosing applies.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our ToolsACE veterinary team built this calculator on the standard Plumb's Veterinary Drug Handbook cephalexin dosing range (22-30 mg/kg every 8-12 hours), cross-referenced with the ACVIM antimicrobial use guidelines and the ISCAID (International Society for Companion Animal Infectious Diseases) consensus on canine pyoderma treatment. Cephalexin (brand names Keflex in human medicine, Rilexine in veterinary medicine) is the most commonly prescribed first-line antibiotic for canine superficial and deep pyoderma — it is highly active against Staphylococcus pseudintermedius (the dominant skin pathogen in dogs), well absorbed orally, and has an excellent safety profile across decades of clinical use. The calculator covers the full range of commercial formulations: 250 and 500 mg tablets (the most common), 75 / 150 / 300 / 600 mg flavoured chewables (Rilexine brand), and 125 or 250 mg / 5 mL oral suspension liquid for small dogs and puppies. Per-dose mg, units (tablets / chewables / mL) per dose, daily total, daily mg/kg ratio, and a 5-band size classification (toy / puppy → giant) are all computed in one pass alongside a 13-breed reference table to sanity-check the result.

Plumb's Veterinary Drug HandbookACVIM Antimicrobial GuidelinesISCAID Canine Pyoderma Consensus

Disclaimer

Estimates only — always consult your veterinarian before giving cephalexin or any prescription medication to your dog. Cephalexin is a Rx-only veterinary antibiotic; standard dose range is 22-30 mg/kg every 8-12 hours, but exact dose, frequency, and course length must be set by your vet based on infection type, severity, bacterial sensitivity (culture if no improvement in 5-7 days), kidney function, pregnancy / lactation status, and concurrent medications. Complete the full prescribed course (typically 10-14 days for pyoderma, 7-14 days for UTI) even if symptoms resolve early. Cephalexin is NOT effective against MRSP, MRSA, Pseudomonas, anaerobes, or fungal infections. For severe allergic reactions (facial swelling, difficulty breathing), seek emergency veterinary care immediately. Source data: Plumb's Veterinary Drug Handbook (10th ed., 2023), ACVIM Antimicrobial Use Guidelines (2017), ISCAID Canine Pyoderma Consensus (2014, updated 2020).