About

Cephalexin (cefalexin) is a first-generation cephalosporin antibiotic prescribed for feline bacterial infections including skin and soft tissue wounds, urinary tract infections, and bone infections. The standard therapeutic range is 10 - 25 mg/kg administered every 8 - 12 hours, but dosing errors are common because commercial formulations vary in concentration (25 mg/mL, 50 mg/mL, 100 mg/mL suspensions; 250 and 500 mg capsules). Underdosing promotes antimicrobial resistance. Overdosing increases the risk of gastrointestinal adverse effects (vomiting, diarrhea) and, in rare cases, nephrotoxicity. This calculator applies weight-based dosing per Plumb's Veterinary Drug Handbook and rounds liquid volumes to 0.1 mL precision suitable for oral syringes.

Note: this tool approximates dosing for otherwise healthy adult cats. Neonatal kittens, cats with renal insufficiency (GFR < 30 mL/min), or cats on concurrent nephrotoxic drugs require veterinary adjustment. Cephalexin is not effective against Pseudomonas spp. or anaerobes. Always confirm culture and sensitivity results before prolonged therapy.

Formulas

The per-dose amount of cephalexin is calculated from the cat's body weight and the selected dose rate:

D = W × R

Where D = single dose (mg), W = body weight (kg), and R = dose rate (mg/kg).

For oral suspension, the volume per dose is:

V = DC

Where V = volume per dose (mL) and C = suspension concentration (mg/mL).

For tablets or capsules, the number of units per dose is:

N = DS

Where S = tablet/capsule strength (mg). Weight conversion when input is in pounds: W_kg = W_lb × 0.453592. Total supply over the treatment course: T = N_doses/day × days.

Reference Data

Infection Type	Dose Range	Frequency	Typical Duration	Notes
Skin & soft tissue (mild)	10 - 15 mg/kg	q12h	7 - 14 days	Superficial pyoderma, small abscesses
Skin & soft tissue (moderate)	15 - 22 mg/kg	q8 - 12h	14 - 21 days	Deep pyoderma, bite wounds
Skin & soft tissue (severe)	22 - 30 mg/kg	q8h	21 - 28 days	Cellulitis, surgical site infections
Urinary tract infection (uncomplicated)	10 - 15 mg/kg	q8 - 12h	10 - 14 days	Confirm gram-positive susceptibility
Urinary tract infection (complicated)	15 - 25 mg/kg	q8h	14 - 28 days	Recurrent UTI; culture guided
Bone & joint infection	22 - 30 mg/kg	q8h	28 - 42 days	Osteomyelitis; long-term therapy
Respiratory (upper, mild)	10 - 15 mg/kg	q12h	7 - 10 days	Secondary bacterial rhinitis
Respiratory (lower)	15 - 25 mg/kg	q8h	14 - 21 days	Bacterial pneumonia
Dental prophylaxis	22 mg/kg	q12h	5 - 7 days	Perioperative; start 24h pre-op
Post-surgical prophylaxis	15 - 22 mg/kg	q8 - 12h	5 - 10 days	Clean-contaminated wounds
Otitis media	15 - 25 mg/kg	q8h	14 - 21 days	If gram-positive confirmed
Wound infection (fight abscess)	15 - 22 mg/kg	q8h	10 - 14 days	Drain if fluctuant; consider anaerobic cover
Staphylococcal folliculitis	22 - 25 mg/kg	q8h	21 - 28 days	Continue 7 days past clinical resolution

Frequently Asked Questions

Cephalexin dosing depends on infection severity, bacterial susceptibility, and tissue penetration requirements. A superficial skin infection may respond to the low end of the range (10 mg/kg), while osteomyelitis demands the upper range (30 mg/kg). Your veterinarian selects within the range based on culture results and the cat's clinical response.

Cephalexin capsules contain powder and can be opened and divided, but accurate splitting requires a precision scale. A 4 kg cat on 15 mg/kg needs 60 mg - that is 12% of a 500 mg capsule, making volumetric division unreliable. Oral suspension (25 mg/mL or 50 mg/mL) is strongly preferred for cats under 5 kg because it allows dosing to 0.1 mL precision with an oral syringe.

Cephalexin is >90% renally excreted. In cats with azotemia (creatinine > 2.5 mg/dL), the elimination half-life extends from the normal 1-2 hours to potentially 4-6 hours. Dose interval should be extended to q12-24h or dose reduced by 50%, depending on GFR. This calculator assumes normal renal function - always consult your veterinarian for cats with kidney disease.

Cephalexin is generally considered safe in neonatal kittens, but pharmacokinetic data in cats under 4 weeks is limited. Neonatal hepatic and renal immaturity can slow drug clearance. Dose at the lower end of the range (10 mg/kg q12h) and use liquid formulation for accurate measurement. Monitor closely for GI signs.

GI upset occurs in approximately 10-15% of cats on cephalexin. Administering with a small amount of food reduces gastric irritation without significantly affecting absorption. If vomiting occurs within 15 minutes of dosing, redose fully. If vomiting occurs after 30 minutes, the dose was likely absorbed. Persistent vomiting over 2+ days warrants switching antibiotics.

Cephalexin has relatively few drug interactions. Concurrent use with aminoglycosides (gentamicin) may increase nephrotoxicity risk. Probenecid delays renal excretion and raises serum levels. Antacids and sucralfate can reduce oral absorption - separate dosing by at least 2 hours. It does not interact with most common feline medications (meloxicam, buprenorphine, fluoxetine).