# Cefazolin: veterinary dose and monograph

> Cefazolin is a veterinary antibiotic. 1st-generation cephalosporin with very high tissue concentrations — drug of choice for surgical antibiotic prophylaxis in dogs / cats / horses. Indications include surgical antibiotic prophylaxis (small animal & equine soft tissue / orthopaedic surgery); skin / soft tissue infections (Streptococcus, methicillin-susceptible Staphylococcus); osteomyelitis (susceptible Gram-positives). This monograph lists 9 reference doses for dogs, cats, horses and reptiles, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/cefazolin · Last reviewed: 2026-10-01

## 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

*Cefazolin doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 10–30 mg/kg | IV | q8h | — |
| Surgical prophylaxis | 22 mg/kg | IV | q90min intra-op | — |
| Sepsis / severe systemic infection | 20–25 mg/kg | IV | q4–8h | — |
| Constant-rate infusion | 1.2 mg/kg/h | IV | CRI after 1.3 mg/kg IV load | — |

- 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

*Cefazolin doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 10–30 mg/kg | IV | q8h | — |
| Surgical prophylaxis | 22 mg/kg | IV | q90min intra-op | — |

- 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

*Cefazolin doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Adult — susceptible infection (slow IV) | 25 mg/kg | IV | q6–8h | — |
| Foal — septicaemia | 15–20 mg/kg | IV | q8–12h | — |

- 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

*Cefazolin doses for reptiles*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Chelonians — susceptible infection | 22 mg/kg | IM | q24h | — |

- 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

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

> **Caution:** 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

> **Caution:** 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](https://vetmasterji.com/drugs/ampicillin)
- [Apramycin](https://vetmasterji.com/drugs/apramycin)
- [Azithromycin](https://vetmasterji.com/drugs/azithromycin)
- [Cefadroxil](https://vetmasterji.com/drugs/cefadroxil)
- [Cefixime](https://vetmasterji.com/drugs/cefixime)
- [Cefoperazone](https://vetmasterji.com/drugs/cefoperazone)
- [Cefotaxime](https://vetmasterji.com/drugs/cefotaxime)
- [Cefovecin](https://vetmasterji.com/drugs/cefovecin)

## Frequently asked questions

### What is the dose of Cefazolin for dogs?

Reference doses for Cefazolin in dogs: 10–30 mg/kg IV q8h (Susceptible infection); 22 mg/kg IV q90min intra-op (Surgical prophylaxis); 20–25 mg/kg IV q4–8h (Sepsis / severe systemic infection); 1.2 mg/kg/h IV CRI after 1.3 mg/kg IV load (Constant-rate infusion). Confirm against the label and the patient before use.

### What is the dose of Cefazolin for cats?

Reference doses for Cefazolin in cats: 10–30 mg/kg IV q8h (Susceptible infection); 22 mg/kg IV q90min intra-op (Surgical prophylaxis). Confirm against the label and the patient before use.

### What is the dose of Cefazolin for horses?

Reference doses for Cefazolin in horses: 25 mg/kg IV q6–8h (Adult — susceptible infection (slow IV)); 15–20 mg/kg IV q8–12h (Foal — septicaemia). Confirm against the label and the patient before use.

### When should Cefazolin not be used?

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.

### What are the side effects of Cefazolin in animals?

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.