What Is Cefazolin and How Does It Work?

Cefazolin is an antibiotic used to treat a wide variety of bacterial infections. It may also be used before and during certain surgeries to help prevent infection. This medication is known as a cephalosporin antibiotic. It works by stopping the growth of bacteria.

  • Cefazolin is available under the following different brand names: Kefzol and Ancef.

What Are Dosages of Cefazolin?

Dosages of Cefazolin:

Dosage Forms and Strengths

Powder for injection

  • 500 mg
  • 1 g
  • 2 g
  • 10 g
  • 20 g
  • 100 g
  • 300 g

Dosage Considerations – Should be Given as Follows:

Moderate-to-Severe Infections

  • 0.5-1 g intravenously (IV) every 6-8 hours

Mild Infections With Gram-Positive Cocci

  • Adult: 250-500 mg intravenously (IV) every 8 hours
  • Infants and children: 25-100 mg/kg/day intravenously/intramuscularly (IV/IM) divided every 6-8 hours; not to exceed 6 g/day
  • Neonates (under 28 days)
    • Under 7 days: 40 mg/kg/day IV/IM divided every 12 hours
    • Greater than 7 days, less than 2 kg: 40 mg/kg/day IV/IM divided every 12 hours
    • Greater than 7 days, greater than 2 kg: 60 mg/kg/day IV/IM divided every 8 hours

Mild-to-Moderate Cholecystitis

  • 1-2 g intravenously (IV) every 8 hours for 4-7 days

Uncomplicated Urinary Tract Infection

  • 1 g intravenously (IV) every 12 hours

Preparation for Surgery

There are no dosing recommendations for pediatric patients for perioperative prophylaxis or for pediatric patients with renal impairment

What Are Side Effects Associated with Using Cefazolin?

Common side effects of cefazolin include:

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Cefazolin?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns, or for more information about this medicine.

What Are Warnings and Precautions for Cefazolin?


This medication contains cefazolin. Do not take Kefzol or Ancef if you are allergic to cefazolin or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


  • Documented hypersensitivity

Effects of Drug Abuse

  • None

Short-Term Effects

  • See "What Are Side Effects Associated with Using Cefazolin?"

Long-Term Effects

  • Prolonged treatment may be associated with an increased international normalized ratio (INR).
  • See "What Are Side Effects Associated with Using Cefazolin?"


  • Endocarditis prophylaxis is recommended only for high-risk patients, per American Heart Association (AHA) guidelines
  • The dose must be adjusted in severe renal insufficiency (high doses may cause central nervous system [CNS] toxicity); superinfections and promotion of non-susceptible organisms may occur with prolonged use or repeated therapy
  • Prolonged treatment, hepatic or renal disease, or nutritional deficiency may be associated with increased international normalized ratio (INR)
  • Prolonged use is associated with fungal or bacterial superinfection
  • Use with caution in patients with seizure disorder (high levels are associated with increased risk of seizures)
  • Use with caution in renal impairment

Pregnancy and Lactation

  • Cefazolin may be acceptable for use during pregnancy. Either animal studies show no risk but human studies are not available or animal studies showed minor risks and human studies were done and showed no risk.
  • Cefazolin is excreted in breast milk. Use caution if breastfeeding. The American Academy of Pediatrics (AAP) committee states that cefazolin is compatible with nursing.
Medscape. Cefazolin.
RxList. Cefazolin Side Effects Drug Center.

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