Cephalexin

Cephalexin is an orally active first-generation cephalosporin used extensively in small-animal medicine. Its principal clinical role is treatment of susceptible staphylococcal skin infections in dogs, with additional applications in soft-tissue, urinary and selected musculoskeletal infections. Its antibacterial spectrum emphasizes gram-positive cocci and a narrower range of gram-negative organisms.

Group

First-generation cephalosporin

Mechanism of Action

Cephalexin binds penicillin-binding proteins involved in cell-wall construction and inhibits peptidoglycan cross-linking. The weakened bacterial wall cannot withstand normal osmotic forces, producing bactericidal activity during active growth. Its effect is time dependent. The spectrum includes susceptible staphylococci and streptococci, with additional activity against selected Escherichia coli, Proteus mirabilis and Klebsiella isolates.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Pyoderma, skin and soft-tissue infections	22–25 mg/kg	PO	Every 12 h
Urinary tract infection	22–25 mg/kg	PO	Every 12 h
Deep or superficial pyoderma	22–33 mg/kg	PO	Every 8–12 h
Recurrent pyoderma	22 mg/kg	PO	Every 12 h	For deep pyoderma a separate eight-hour alternative is described.
Deep pyoderma	22 mg/kg	PO	Every 8 h
Superficial pyoderma	30–40 mg/kg	PO	Every 24 h	Up to 28 days
Pyoderma	22–35 mg/kg	PO	Every 12 h
Respiratory infection	20–40 mg/kg	PO	Every 8 h
Soft-tissue infection	30–50 mg/kg	PO	Every 12 h
Systemic infection	25–60 mg/kg	PO	Every 8 h
Orthopedic infection	22–30 mg/kg	PO	Every 6–8 h	Up to 28 days
Pyometra or metritis adjunct	10–30 mg/kg	PO	Every 8–12 h	Antibiotic dosing is only one part of pyometra management; assess source control and systemic illness.
Urinary tract infection	30–40 mg/kg	PO	Every 8 h	Historical alternatives specify acute cystitis 7–10 days, chronic disease up to four weeks and pyelonephritis 4–8 weeks; use an infection-specific current treatment plan.
Neonatal bacterial infection	10–30 mg/kg	PO	Every 8–12 h	Neonates only; weak patients require safe assisted feeding/administration rather than forced oral dosing.
Secondary bacterial infection with juvenile cellulitis	20 mg/kg	PO	Every 8 h	Puppies 3–16 weeks. Juvenile cellulitis itself is not established as a primary bacterial disease; use only for a separate bacterial indication.
Infectious otitis	22 mg/kg	PO	Every 12 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infections	22–25 mg/kg	PO	Every 12 h
Soft-tissue infection	30–50 mg/kg	PO	Every 12 h
Systemic infection	35 mg/kg	PO	Every 6–8 h
Bacterial infections	22 mg/kg	PO	Every 8 h	Give with food if gastrointestinal upset occurs.
Gram-positive infection	22 mg/kg	PO	Every 12 h
Gram-negative infection	30 mg/kg	PO	Every 8 h
Bacterial infections	20–40 mg/kg	PO	Every 8 h

Horses

Use / stage	Dose	Route	Schedule	Instructions
Susceptible gram-positive infection	30 mg/kg	PO	Every 8 h	Only highly susceptible bacteria with MIC ≤0.5 mcg/mL; equine oral absorption is very low.
Bacterial infections	22–33 mg/kg	PO	Every 6 h	Oral absorption is poor; use only for a sufficiently susceptible organism.

Rabbits

Use / stage	Dose	Route	Schedule	Instructions
Historical oral cephalexin treatment	Reference only	PO		11–22 mg/kg orally every eight hours appears in the older source. Oral cephalosporins can cause serious dysbiosis in rabbits; do not treat this as a routine first-line rabbit regimen.

Guinea pigs

Use / stage	Dose	Route	Schedule	Instructions
Historical injectable cephalexin treatment	Reference only	IM		50 mg/kg IM daily is described; no compatible veterinary injectable preparation is established here and serious dysbiosis is a concern.

Ferrets

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infections	15–25 mg/kg	PO	Every 8–12 h

Birds

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infections	35–50 mg/kg	PO	Every 6 h	Oral suspension.
Alternative bacterial infection treatment	40–100 mg/kg	PO	Every 6 h

Ratites

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infections	15–22 mg/kg	PO	Every 8 h
Historical megabacteriosis treatment	Reference only	PO		The older passage lists 50 mg/kg orally four times daily for five days, but megabacteriosis is associated with Macrorhabdus, a yeast. This is not promoted as an antibacterial treatment for that organism.

Indications

Treatment of susceptible staphylococcal pyoderma and other bacterial skin infections in dogs.
Treatment of susceptible wounds, abscesses and soft-tissue infections in dogs and cats.
Treatment of selected susceptible bacterial urinary tract infections in dogs and cats.
Treatment of susceptible bone and joint infections, including osteomyelitis, within an appropriate veterinary treatment plan.

Contraindications

Cephalosporin hypersensitivity; assess prior severe beta-lactam allergy.

Interactions

Avoid mixing with other drugs in the same vial or syringe unless compatibility is established.

Adverse effects

Hypersensitivity
Gastrointestinal upset
Injection-site reactions with parenteral products

Preparations

Preparation	Form	Strength	Route
Cephalexin 75 mg tablet	Tablet	75 mg / tablet	PO
Cephalexin 150 mg tablet	Tablet	150 mg / tablet	PO
Cephalexin 300 mg tablet	Tablet	300 mg / tablet	PO
Cephalexin 600 mg tablet	Tablet	600 mg / tablet	PO
Cephalexin 100 mg/mL oral liquid	Oral Liquid	100 mg / mL	PO
Cephalexin suspension 125 mg/5 mL	Oral Liquid	125 mg / 5 mL	PO
Cephalexin suspension 250 mg/5 mL	Oral Liquid	250 mg / 5 mL	PO
Cephalexin 250 mg capsule	Capsule	250 mg / capsule	PO
Cephalexin 500 mg capsule	Capsule	500 mg / capsule	PO

Monitoring and Administration

Choose treatment using organism identity, infection site and susceptibility testing. Reassess clinical response and renal function where impaired clearance may increase exposure.

Food-animal authorization and withdrawal periods depend on the exact formulation, species, regimen and jurisdiction; do not transfer foreign approvals or residue intervals to another product.

Refrigerate suspension and discard after 14 days. Enteral admixtures are for immediate use.

Cephalexin may interfere with urine glucose tests. Methicillin-resistant staphylococci are clinically resistant; cephalothin is not a preferred susceptibility marker.

Septic shock and severe systemic illness can reduce oral absorption; use a suitable parenteral antibacterial instead of relying on a high oral dose.

Historical long treatment durations are not automatic minimums. Reassess site, culture, source control and response rather than carrying an old duration into every infection.