Cefazolin
Cefazolin sodium
Also known as: Ancef · Kefzol · Zolicef · 46083 · cefazolinum natricum · cephazolin sodium · SKF-41558
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceSusceptible infections (extra-label)
Verified clinician required
- q6-8h
NA
Governing clinical context (4)
- 1. If injecting IM, the drug must be injected into a large muscle mass.
- 2. IV injections should be given slowly (ie, over 3 to 5 minutes).
- Cefazolin sodium powder for injection and solutions for injection should be protected from light. The powder for injection should be stored at room temperature (20°C-25°C [68°F-77°F]) but may be exposed to 15°C to 30°C (59°F-86°F) temperatures; temperatures above 40°C (104°F) should be avoided. The frozen solution for injection should be stored at temperatures no higher than -20°C (-4°F).
- After reconstitution, the solution will be stable for 24 hours if kept at room temperature or for 10 days if refrigerated (5°C [41°F]). If, after reconstitution, the solution is immediately frozen in the original container, the preparation will be stable for at least 12 weeks when stored at -20°C (-4°F).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Cefazolin is a parenteral first-generation cephalosporin antibiotic widely used in veterinary medicine. Although not FDA-approved for veterinary species, it is a clinical workhorse for surgical prophylaxis (especially orthopedic and soft tissue procedures) and the treatment of systemic infections, including sepsis.
Clinical Pearls:
- Spectrum of Activity: Exhibits excellent coverage against most Gram-positive pathogens (e.g., Staphylococcus intermedius, S. aureus, Streptococcus spp.) and variable to poor coverage against Gram-negative pathogens. It is highly effective against most anaerobes, with the notable exception of Bacteroides fragilis.
- Pharmacodynamics: It is a time-dependent bactericidal antibiotic. Efficacy relies on keeping the drug concentration at the site of infection above the Minimum Inhibitory Concentration (MIC) for the majority of the dosing interval. Constant rate intravenous infusion (CRI) protocols are increasingly utilized to optimize this parameter.
- Administration: Must be given parenterally (IV, IM, SC, IO) as it is not appreciably absorbed orally. IV injections should be administered slowly over 3-5 minutes to minimize adverse reactions.
Mechanism of action
Cefazolin is a bactericidal beta-lactam antibiotic.
Mechanism of Action:
- Target: Binds to specific Penicillin-Binding Proteins (PBPs) located inside the bacterial cell wall.
- Pathway: Beta-lactam ring binds PBPs → Inhibition of the transpeptidation enzyme → Prevention of peptidoglycan cross-linking → Weakening of the bacterial cell wall.
- Result: The defective cell wall makes the bacteria highly susceptible to osmotic pressure, leading to cell lysis and death.
As a time-dependent antibiotic, its bacterial killing is maximized by optimizing the duration of time that free drug concentrations remain above the MIC (T > MIC).
Safety & warnings
Contraindications
- Patients with a known history of hypersensitivity to cephalosporins
Adverse effects
- Hypersensitivity reactions (rashes, fever, eosinophilia, anaphylaxis)
- Pain at the IM injection site
- Sterile abscesses or local tissue reactions (rare)
- Thrombophlebitis (following IV administration)
- Nephrotoxicity (minimal risk at clinical doses)
- Neurotoxicity or seizures (associated with very high IV doses)
- GI flora disruption (in nursing neonates)
Precautions
Use cautiously in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., penicillins, carbapenems) due to the potential for cross-reactivity. Dosage adjustments may be necessary in patients with severe renal failure, as the drug is primarily excreted unchanged by the kidneys. Safe use during pregnancy has not been firmly established (FDA Category B), though teratogenic effects have not been documented; use only when benefits outweigh risks. Cefazolin is distributed into milk and may alter neonatal gut flora in nursing dams.
Drug interactions
Potential for additive nephrotoxicity; use concurrently with caution.
Potential for additive nephrotoxicity; use concurrently with caution.
Competitively blocks the renal tubular secretion of cefazolin, thereby increasing serum levels and prolonging the elimination half-life.
Monitoring
- Clinical efficacy (resolution of clinical signs, normalization of WBC count, fever reduction)
- Renal function (BUN, creatinine, urinalysis) in patients with pre-existing renal impairment
- Signs of hypersensitivity or injection site reactions
Pharmacokinetics
Half-life
Absorption
Not appreciably absorbed after oral administration; must be given parenterally. In dogs, peak levels occur approximately 30 minutes after IM administration.
Distribution
Apparent volume of distribution at steady state: 700 mL/kg (dogs), 190 mL/kg (horses), 165 mL/kg (calves). Plasma protein binding is approximately 16-28% in dogs and 4-8% in horses. Crosses the placenta and is distributed into milk.
Metabolism
Minimal to no hepatic metabolism.
Elimination
Excreted unchanged by the kidneys into the urine. In dogs, approximately 64% of clearance is attributed to renal tubular secretion. Elimination half-lives may be significantly prolonged in patients with severely diminished renal function.
Overdose
Cephalosporin overdoses are unlikely to cause significant problems. However, very high doses given rapidly IV could potentially cause seizures or neurotoxicity. Treatment for overdose should be supportive and symptomatic.
Available products
Formulations
- Powder for injection
- Solution for injection (IV infusion)
Human-labeled
- Cefazolin Sodium Powder for Injection: 500 mg, 1 g, 5 g, 10 g, & 20 g in vials & piggyback vials
- Cefazolin Sodium for Injection (IV infusion): 1 g in 50 mL plastic containers or duplex bags
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Protect powder and solutions from light. Store powder at room temperature (15-30°C); avoid temperatures above 40°C. After reconstitution, the solution is stable for 24 hours at room temperature, 96 hours if refrigerated, or at least 12 weeks if immediately frozen at -20°C.
Client information
Cefazolin is an injectable antibiotic that is typically administered by your veterinarian in a clinic or hospital setting, most commonly to prevent infection during surgery or to treat severe systemic infections.
Important Note: Because this medication is given via injection (intravenously or intramuscularly), you will not need to administer it at home.
- Allergic Reactions: While rare, if your pet exhibits signs of an allergic reaction after returning home (such as facial swelling, hives, or difficulty breathing), contact your veterinarian immediately.
- Injection Site: Your pet may experience mild soreness at the injection site. If you notice severe swelling, redness, or pain, let your veterinary team know.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.