Cefazolin: veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Kefzol, Ancef

Species with doses

Dogs, Cats, Horses and Reptiles

General dose range

10–30 mg/kg IV q6–8h — check the species tables for the indication

Routes

IV, IM

Last reviewed

1 October 2026

Indications

• Surgical antibiotic prophylaxis (small animal & equine soft tissue / orthopaedic surgery)
• Skin / soft tissue infections (Streptococcus, methicillin-susceptible Staphylococcus)
• Osteomyelitis (susceptible Gram-positives)
• UTI (susceptible E. coli, Proteus)
• Equine foal septicaemia adjunct

Cefazolin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Susceptible infection: Plumb's p.210 (Aucoin 2000): gram-positive 10 mg/kg IV/IM q8h, range 10–30 mg/kg IV q8h; gram-negative 30 mg/kg IM/SC or 10–30 mg/kg IV q8h. Papich 5th ed p.170: 25 mg/kg q6h IV/IM. CORRECTION (2026-08-26 audit): previously 5–10 mg/kg, which sat below both references. IM form not interchangeable with IV.
• Surgical prophylaxis: Papich 5e: 22 mg/kg IV, repeated every 2 h during surgery. Plumb’s p.210 (Trepanier 2003): orthopaedic surgery 20 mg/kg IV at induction then every 90 min until closure; soft-tissue surgery 20 mg/kg IV at surgery and a second 20 mg/kg SC 6 h later.
• Sepsis / severe systemic infection: Plumb's p.210 (Hardie 2000): "For sepsis: 20–25 mg/kg IV q4–8h". Papich 5th ed p.170 concurs at 25 mg/kg q6h IV/IM. CORRECTION (2026-08-26 audit): this row previously read 5–7.5 mg/kg — an approximately 4× UNDERDOSE on the entry's most critical indication. The older 3–7.5 mg/kg figure (Greene 2006) is a low-end susceptible-infection dose and must not be used for sepsis.
• Constant-rate infusion: Papich 5e (dogs and cats): 1.3 mg/kg IV loading dose followed by 1.2 mg/kg/h.

Cats

• Susceptible infection: Plumb’s p.210: Gram-positive 10 mg/kg IV or IM q8h, range 10–30 mg/kg IV q8h; Gram-negative 30 mg/kg IM/SC or 10–30 mg/kg IV q8h (Aucoin); 20–25 mg/kg q8h (Lappin); systemic 33 mg/kg q8–12h (Greene). Papich 5e (dogs and cats): 25 mg/kg q6h IV or IM. Give IV over at least 3–5 min.
• Surgical prophylaxis: Papich 5e: 22 mg/kg IV every 2 h during surgery. Plumb’s p.210 (Trepanier 2003): orthopaedic 20 mg/kg IV at induction then every 90 min until closure; soft tissue 20 mg/kg IV then 20 mg/kg SC 6 h later.

Horses

• Adult — susceptible infection (slow IV): Papich 5e: horses 25 mg/kg q6h IM or IV. Plumb’s p.210: 25 mg/kg IV or IM q6h (Bertone 2003) or q6–8h (Papich 2003). Give IV over at least 3–5 minutes.
• Foal — septicaemia: Plumb’s p.210: foals 20 mg/kg IV q8–12h (Caprile & Short 1987; Brumbaugh 1999); neonatal foals 15–20 mg/kg IV q8h (Magdesian 2003).

Reptiles

• Chelonians — susceptible infection: Plumb’s p.210 (Johnson 2002): chelonians 22 mg/kg IM q24h.

Contraindications

Hypersensitivity to cephalosporins (~10 % cross-reactivity with penicillins). Reduce dose in severe renal impairment. NOT FDA-approved in food animals — extra-label use requires FARAD-verified withdrawal.

Species-specific warnings

Rabbits: Avoid — cephalosporins risk fatal clostridial enterotoxaemia in rabbits / guinea pigs.

Horses: Slow IV (over 10 min) preferred. IM ok if mixed with 1 % lidocaine.

Adverse effects

• GI upset (vomiting / soft stool)
• Local pain on IM injection — mix with 1 % lidocaine in IV-restricted patients
• Hypersensitivity (urticaria, rare anaphylaxis)
• Rare neutropenia / thrombocytopenia with prolonged use

Drug interactions

• Aminoglycosides: synergistic vs many Gram-negatives — but do not mix in same syringe (physical incompatibility)
• Loop diuretics / nephrotoxins: additive nephrotoxicity in dehydrated patients
• Probenecid: prolongs cefazolin half-life

Pregnancy and lactation

Generally considered safe; FDA Category B (human extrapolation). Used routinely for cesarean section antibiotic prophylaxis.

Monitoring

• Surgical prophylaxis: redose every 90 min during prolonged surgery — maintain tissue levels
• Renal function on prolonged courses
• Hypersensitivity signs on first dose

Clinical pearls

• Surgical prophylaxis: 22 mg/kg IV 30 min pre-incision is the small-animal standard — repeat every 90 min if surgery exceeds 2 h
• Clean-contaminated abdominal surgery: cefazolin + metronidazole covers Gram-positives + anaerobes; add ampicillin if Enterococcus likely
• IM injection is painful — mix with 1 % lidocaine equal-volume for IM use, do NOT use that mixed product IV
• Reconstituted vial is good for 96 h refrigerated — fits a typical surgery day without waste
• Equine foals with septicaemia: cefazolin 10–20 mg/kg IV q6h is a solid starting empiric while culture is pending

Mechanism of action

1st-generation cephalosporin. Binds penicillin-binding proteins (PBPs) — inhibits transpeptidase cross-linking of peptidoglycan, causing bacterial lysis. Time-dependent bactericidal activity. Strongest spectrum on Gram-positives (Streptococcus, methicillin-susceptible Staphylococcus); modest Gram-negative coverage (E. coli, Proteus, some Klebsiella). Excellent bone and synovial fluid penetration — hence the surgical prophylaxis role.

Formulations and products

• Cefazolin sodium 500 mg / 1 g powder vial reconstituted to 330 mg/mL (Papich 5e p.140 — diluent volume per vial label)
• Cefazolin sodium 500 mg / 1 g powder vial reconstituted to 275 mg/mL (Papich 5e p.140 — diluent volume per vial label)
• Cefazolin sodium premixed IV infusion 1 g in 50 mL (20 mg/mL — Plumb’s p.211)

Storage

Powder vial 15–30 °C protected from light. Reconstituted solution stable 24 h at room temp / 96 h refrigerated.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antibiotics

• Ampicillin
• Apramycin
• Azithromycin
• Cefadroxil
• Cefixime
• Cefoperazone
• Cefotaxime
• Cefovecin

Frequently asked questions