Cephalexin for Dogs Dosage Calculator
Compute cephalexin dogs dosage using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Dose (mg) = Weight (kg) x Dose Rate (mg/kg); Tablets = Dose / Tablet Strength (round to nearest 0.5)
The cephalexin dose is calculated by multiplying the dog's body weight in kilograms by the prescribed dose rate (typically 22-30 mg/kg). For tablets, the result is divided by the tablet strength and rounded to the nearest half tablet. For liquid formulations, the dose is divided by the concentration (mg/ml). Total medication needed is the daily dose multiplied by treatment duration.
Worked Examples
Example 1: Skin Infection in Medium Dog
Problem:Calculate cephalexin dose for a 50-lb dog with superficial pyoderma using 500mg tablets.
Solution:Weight: 50 lbs = 22.7 kg\nStandard dose: 26 mg/kg (midpoint)\nDose: 26 x 22.7 = 590 mg per administration\n500mg tablets: 590/500 = 1.2 → round to 1 tablet\nPractical dose: 500 mg (22 mg/kg)\nFrequency: Twice daily for 21 days\nTotal tablets: 1 x 2 x 21 = 42 tablets
Result:1 tablet (500 mg) twice daily for 21 days | 42 tablets total
Example 2: UTI in Small Dog
Problem:Calculate cephalexin dose for a 20-lb dog with UTI using 250mg tablets.
Solution:Weight: 20 lbs = 9.1 kg\nStandard dose: 22.5 mg/kg (midpoint)\nDose: 22.5 x 9.1 = 205 mg per administration\n250mg tablets: 205/250 = 0.82 → round to 1 tablet\nPractical dose: 250 mg (27.5 mg/kg)\nFrequency: Twice daily for 14 days\nTotal tablets: 1 x 2 x 14 = 28 tablets
Result:1 tablet (250 mg) twice daily for 14 days | 28 tablets total
Frequently Asked Questions
What is cephalexin and how does it work in dogs?
Cephalexin (brand names Keflex, Rilexine) is a first-generation cephalosporin antibiotic widely used in veterinary medicine. It works by interfering with bacterial cell wall synthesis, causing the bacteria to burst and die. Cephalexin is bactericidal, meaning it actively kills bacteria rather than just stopping their growth. It is effective against most gram-positive bacteria (Staphylococcus, Streptococcus) and some gram-negative bacteria commonly responsible for skin, urinary, respiratory, and soft tissue infections in dogs. Cephalexin is one of the most commonly prescribed oral antibiotics in veterinary practice due to its broad effectiveness, good safety profile, and relatively low cost. It is well-absorbed from the gastrointestinal tract and reaches therapeutic concentrations in most body tissues.
What is the standard cephalexin dosage for dogs?
The standard veterinary dosage of cephalexin for dogs is 22-30 mg per kilogram of body weight, given twice daily (every 12 hours). For some infections, particularly bone infections, a dose of 22-30 mg/kg given three times daily (every 8 hours) may be prescribed. In practical terms, a 50-pound (23 kg) dog would typically receive 500-750 mg per dose twice daily. Treatment duration varies significantly by infection type: skin infections require 14-28 days (or longer for deep infections), UTIs typically 7-14 days, and bone infections may need 6-8 weeks. The most important principle is to complete the full prescribed course even if symptoms resolve, as stopping early promotes antibiotic resistance and infection recurrence.
What are the side effects of cephalexin in dogs?
Cephalexin is generally well-tolerated in dogs, but side effects can occur. The most common are gastrointestinal effects including vomiting, diarrhea, and decreased appetite, affecting approximately 5-10% of patients. Giving the medication with food can significantly reduce GI upset. Less common side effects include drooling (especially with liquid formulations), panting, and skin reactions. Rare but potentially serious effects include allergic reactions (hives, facial swelling, difficulty breathing), which require immediate veterinary attention. Prolonged use can lead to overgrowth of resistant organisms or yeast infections. Dogs with known allergies to cephalosporins or penicillins should not receive cephalexin, as there is approximately 10% cross-reactivity between these antibiotic classes.
How long should my dog take cephalexin?
Treatment duration depends entirely on the type and severity of infection. For uncomplicated urinary tract infections, 7-14 days is standard. Simple skin infections (superficial pyoderma) require a minimum of 14-21 days, while deep skin infections may need 4-6 weeks or longer. The general rule for skin infections is to continue treatment for at least 7-14 days beyond clinical resolution of symptoms. Wound and soft tissue infections typically require 10-14 days. Bone infections (osteomyelitis) require prolonged treatment of 6-8 weeks minimum. Never stop antibiotics early because symptoms have improved — premature discontinuation is the leading cause of recurring infections and contributes to antibiotic resistance. Your veterinarian may perform follow-up cultures to confirm the infection has fully resolved.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy