About

Cephalexin is a first-generation cephalosporin antibiotic prescribed for bacterial infections in dogs, including skin pyoderma, urinary tract infections, wound infections, and bone/soft-tissue abscesses. The standard dosing range is 10 - 30 mg/kg administered every 8 - 12 hours depending on the site and severity of infection. Underdosing promotes antimicrobial resistance. Overdosing raises the risk of gastrointestinal disturbance, nephrotoxicity in predisposed patients, and unnecessary cost. This calculator applies weight-based dosing from Plumb's Veterinary Drug Handbook and cross-references common tablet and liquid formulation sizes so you can verify the prescription your veterinarian provides.

The tool approximates dosing assuming normal renal function and adult body weight. Neonatal, geriatric, or renally impaired dogs may require adjusted protocols. It does not replace veterinary diagnosis. Always confirm the selected dose rate, frequency, and treatment duration with your prescribing veterinarian before administering any medication.

Formulas

The per-dose amount is calculated by multiplying the dog's body weight in kilograms by the selected dose rate:

D = W × R

where D = single dose in mg, W = body weight in kg, R = dose rate in mg/kg.

Total daily dose depends on frequency:

D_daily = D × f

where f = number of doses per day (2 for q12h, 3 for q8h).

For liquid suspension, the volume per dose is:

V = DC

where V = volume in mL and C = suspension concentration in mg/mL (commonly 25 or 50 mg/mL).

For weight conversion from pounds: W_kg = W_lb ÷ 2.2046.

Reference Data

Infection Type	Dose Rate	Frequency	Typical Duration	Notes
Superficial Pyoderma	15 mg/kg	q12h	21 - 28 days	Continue 7 days past clinical resolution
Deep Pyoderma	22 - 30 mg/kg	q8-12h	42 - 84 days	Culture & sensitivity recommended
Urinary Tract Infection (simple)	15 - 20 mg/kg	q12h	10 - 14 days	Recheck urinalysis after course
Urinary Tract Infection (complicated)	20 - 30 mg/kg	q8h	28 - 42 days	Concurrent imaging may be indicated
Wound / Abscess	20 - 25 mg/kg	q8-12h	10 - 21 days	Drain if fluctuant
Bone / Joint Infection	22 - 30 mg/kg	q8h	28 - 56 days	Prolonged course; monitor renal values
Respiratory (upper)	15 - 20 mg/kg	q12h	7 - 14 days	Often secondary to viral; assess underlying cause
Soft Tissue Infection	20 - 25 mg/kg	q8-12h	14 - 28 days	Debridement may be required
Surgical Prophylaxis	22 mg/kg	Single pre-op dose	1 dose	Given 30 - 60 min before incision
Otitis Media	20 - 30 mg/kg	q8-12h	21 - 42 days	Concurrent topical therapy usually needed
Dental Infection	15 - 22 mg/kg	q12h	7 - 14 days	Source control (extraction) is primary
General / Empirical	15 - 25 mg/kg	q8-12h	7 - 14 days	Adjust on culture results

Frequently Asked Questions

The range reflects infection depth and bacterial load. Superficial pyoderma responds at the lower end (15 mg/kg q12h) because cephalexin concentrates well in skin. Deep-seated infections (bone, complicated UTI) require the upper range (22 - 30 mg/kg q8h) to maintain tissue levels above the MIC (minimum inhibitory concentration) for the entire dosing interval. Your veterinarian selects within this range based on culture results and clinical severity.

Standard cephalexin tablets and capsules are not enteric-coated, so splitting is acceptable. However, capsules cannot be split evenly. For dogs under 5 kg, liquid suspension (25 or 50 mg/mL) is strongly preferred because it allows precise dosing with a syringe. This calculator provides both tablet-count and liquid-volume outputs for this reason.

Premature discontinuation is the primary driver of resistant bacterial populations. For skin infections, clinical guidelines mandate continuing therapy for at least 7 days beyond visible resolution. For deep pyoderma, this extends to 14 days past resolution. Stopping early leaves sub-MIC antibiotic concentrations in tissue, selecting for resistant organisms that complicate future treatment.

Yes. Cephalexin is eliminated primarily by renal excretion. Dogs with elevated creatinine or reduced GFR require dose reduction or extended intervals. This calculator assumes normal renal function. If your dog has known kidney disease, the veterinarian may reduce the dose by 25 - 50% or extend the interval to q24h. Monitoring BUN and creatinine during prolonged courses (over 14 days) is standard practice.

Cephalexin absorption in dogs is not significantly affected by food. However, administering with a small meal reduces the incidence of gastrointestinal side effects (vomiting, diarrhea), which occur in approximately 10 - 15% of patients. Giving the dose with food is the standard recommendation.

Cephalexin has a wide therapeutic index in dogs. A 10% weight estimation error at 20 mg/kg produces a dose variation of 2 mg/kg, which remains within the therapeutic window. However, for toy breeds under 3 kg, even small errors become proportionally large. Weigh toy and miniature breeds on a veterinary scale rather than estimating.