What Cephalexin Treats in Dogs
Cephalexin is a first-generation cephalosporin antibiotic that covers a broad range of gram-positive and some gram-negative bacteria. In dogs, it is most commonly prescribed for bacterial skin infections (pyoderma), which is the most frequent reason dogs receive antibiotics. It is also used for urinary tract infections, wound infections, soft tissue infections, and bone infections (osteomyelitis).
Dosing by Condition
- Superficial pyoderma (surface and shallow skin infections): 10-15 mg/kg every 12 hours for 7-14 days minimum, or 1 week past clinical resolution
- Deep pyoderma (folliculitis, furunculosis, cellulitis): 15-20 mg/kg every 8-12 hours for 4-6 weeks minimum
- Urinary tract infection: 15-20 mg/kg every 8-12 hours for 7-14 days (longer for pyelonephritis)
- Osteomyelitis: 20-30 mg/kg every 12 hours for 6-8 weeks (culture and sensitivity testing recommended)
Why Completing the Full Course Matters
The most common reason bacterial skin infections recur is stopping the antibiotic course when visible symptoms resolve. Clinical improvement typically occurs after 5-7 days of treatment, but the bacterial population in the skin is not yet fully eliminated. Stopping early selects for resistant bacteria, producing recurrent infections that are harder to treat. Complete every course fully, even after the skin looks clear.
Side Effects
Cephalexin is generally well tolerated. The most common side effects are mild gastrointestinal upset: vomiting, decreased appetite, and loose stools. These usually resolve within the first week and are reduced by giving the medication with food. Allergic reactions are rare but possible, particularly in dogs with known penicillin allergy, as cephalosporins and penicillins share a beta-lactam ring structure and carry approximately 10% cross-reactivity.
Drug Interactions and Contraindications
Cephalexin should not be used in dogs with known cephalosporin or penicillin allergy. It may interact with drugs that affect renal tubular secretion. In dogs with kidney disease, the dose interval may need to be extended because cephalexin is eliminated primarily through the kidneys. Your vet will adjust dosing for dogs with reduced kidney function.
Recurrent Skin Infections
Dogs with recurring pyoderma often have an underlying cause: atopic dermatitis (allergic skin disease), hypothyroidism, Cushing's disease, or immune deficiency. Treating the bacterial infection repeatedly without addressing the root cause leads to treatment failure and antibiotic resistance. Culture and sensitivity testing is recommended for dogs with their third or subsequent episode of pyoderma within 12 months.