Medically Reviewed on 4/26/2022

Generic Name: cefazolin

Brand Names: Ancef, Kefzol (discontinued brand)

Drug Class: Cephalosporins, 1st Generation

What is cefazolin, and what is it used for?

Cefazolin is a broad spectrum antibiotic used to treat bacterial infections. Cefazolin is active against many gram-positive and gram-negative bacteria, however, it is a first generation cephalosporin and many strains have developed resistance to it. Gram-positive and gram-negative bacteria are structurally different, identified by the Gram stain lab test. Gram-negative bacteria have an additional membrane outside the cell wall that gram-positive bacteria lack.

Cefazolin kills bacteria by inhibiting the synthesis of peptidoglycan, a vital component that provides stability to the bacterial cell wall. Cephalosporins are beta-lactam antibiotics that contain a beta-lactam ring in their chemical structure. Beta-lactam is a compound that targets and blocks penicillin-binding proteins, enzymes that are essential for the biosynthesis of peptidoglycan. Bacteria develop resistance to beta-lactam antibiotics by producing beta-lactamases, enzymes that cleave the beta-lactam rings in the antibiotics and destroy them. Organisms susceptible to cefazolin include:

  • Gram-positive bacteria: Staphylococcus aureus (methicillin-susceptible strains, including those producing penicillinases), Staphylococcus epidermidis, Group A beta-hemolytic streptococci and other strains of streptococci (many strains of enterococci are resistant), Streptococcus pneumoniae
  • Gram-negative bacteria: Escherichia coli, Klebsiella species, Proteus mirabilis, Haemophilus influenzae, Enterobacter aerogenes

Cefazolin is used to treat the following bacterial infections:

  • Respiratory tract infections
  • Urinary tract infections
  • Skin and skin structure infections
  • Biliary tract infections
  • Bone and joint infections
  • Genital infections
  • Septicemia
  • Endocarditis
  • Perioperative prophylaxis

Off-label uses include:


  • Do not administer cefazolin to patients with known hypersensitivity to cephalosporin group of antibiotics
  • Use cefazolin with caution in patients with a history of penicillin allergy because cross-hypersensitivity among penicillin and beta-lactam antibiotics may occur
  • Endocarditis prophylaxis recommended only for high-risk patients, per American Heart Association (AHA) guidelines
  • Use of nearly all antibacterial agents including cefazolin can lead to Clostridium difficile overgrowth and associated diarrhea or colitis
  • Prolonged or repeated use may result in bacterial and fungal overgrowth of non-susceptible organisms
  • Use of cefazolin injection in the absence of proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of development of drug-resistant bacteria
  • Use with caution in patients with seizure disorders; high doses are associated with increased risk of seizures
  • Cefazolin may increase blood clotting time, particularly in patients with impaired kidney or liver function, poor nutritional state, patients on prolonged antimicrobial therapy and patients previously stabilized on anticoagulant therapy


Bowel regularity means a bowel movement every day. See Answer

What are the side effects of cefazolin?

Common side effects of cefazolin include:

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug.

Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

What are the dosages of cefazolin?

Powder for Injection

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


Moderate-to-Severe Infections

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

Mild Infections with Gram-Positive Cocci

  • 250-500 mg IV every 8 hours

Mild-to-Moderate Cholecystitis

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

Uncomplicated Urinary Tract Infection

  • 1 g IV every 12 hours

Preparation for Surgery

Prophylaxis against infection

  • Preoperatively: 1-2 g intravenous/intramuscular (IV/IM) within 1 hour before procedure (may be repeated in 2-5 hours intraoperatively)
  • Postoperatively: 0.5-1 g IV every 6-8 hours for 24 hours

Surgical infection

  • Cardiac procedures, hysterectomy, oral or pharyngeal procedures, craniotomy, joint replacement, thoracic procedures, arterial procedures, amputation, traumatic wounds; high-risk esophageal, gastroduodenal, or biliary tract procedures: 1-2 g IV
  • Colorectal procedures: 1-2 g IV plus metronidazole 0.5 g IV
  • High-risk cesarean section, 2nd trimester abortion: 1 g IV
  • Ophthalmic procedures: 100 mg subconjunctivally

Endocarditis prophylaxis

  • 1 g IV/IM 30-60 minutes before procedure
  • American Heart Association (AHA) guidelines: Endocarditis prophylaxis recommended only for high-risk patients

Bacterial Keratitis (Off-label)

  • 1 drop instilled into affected eye(s) every 1-2 hours; typically alternated every other hour with antibiotic providing gram-negative coverage (e.g., tobramycin)
  • Extemporaneous compounded fortified cefazolin 50 mg/mL
  • Dilute 500 mg parenteral cefazolin powder in sterile water to form 10 mL solution
  • Store refrigerated; preparation expires in 7 days

Dosing Modifications

Renal impairment

  • CrCl 35-54 mL/min: Give full dose at intervals longer than 8 hours
  • CrCl 10-35 mL/min: Give therapeutic dose every 12 hours
  • CrCl 10 mL/min or less: Give therapeutic dose every 24 hours

Hepatic impairment

  • Not studied

Infections with Gram-Positive Cocci

Neonates (younger than 28 days)

  • Younger than 7 days: 40 mg/kg/day IV/IM divided every 12 hours  
  • Older than 7 days, weight less than 2 kg: 40 mg/kg/day IV/IM divided every 12 hours
  • Older than 7 days, weight greater than 2 kg: 60 mg/kg/day IV/IM divided every 8 hours

Infants & children

  • 25-100 mg/kg/day IV/IM divided every 6-8 hours; not to exceed 6 g/day

Endocarditis Prophylaxis

  • 50 mg/kg IV/IM 30-60 minutes before procedure; not to exceed 1 g  
  • AHA guidelines: Endocarditis prophylaxis recommended only for high-risk patients

Community-Acquired Pneumonia

  • Children 3 months and older: 150 mg/kg/day IV/IM divided every 8 hours (moderate to severe infections, methicillin susceptible S. aureus preferred

Dosing Considerations

  • Cefazolin 2 g for Injection USP and Dextrose Injection USP are not recommended for use in pediatric patients; to avoid unintentional overdose, 1 g cefazolin for Injection USP and dextrose Injection USP should only be used in pediatric patients who require entire contents of 1 g dose and not any fraction of it
  • There are no dosing recommendations for pediatric patients for perioperative prophylaxis or for pediatric patients with renal impairment

What drugs interact with cefazolin?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information.

Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • Available data do not show any evidence of fetal harm with the use of cefazolin during pregnancy and is acceptable for use in pregnant women.
  • Cefazolin is one of the recommended antibiotics that may be used prior to vaginal delivery in patients at high risk for endocarditis. Cefazolin may also be used prior to Cesarean deliveries.
  • Cefazolin is present in very low concentrations in the milk of nursing mothers; use with caution.

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Cefazolin is a broad spectrum antibiotic used to treat bacterial infections, including respiratory tract infections, urinary tract infections, skin infections, biliary tract infections, bone and joint infections, genital infections, and others. Common side effects of cefazolin include injection site reactions, low blood pressure (hypotension), fainting (syncope), abdominal cramps and pain, loss of appetite (anorexia), diarrhea, gas (flatulence), heartburn, oral candida yeast infection (candidiasis), and others.

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You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Medically Reviewed on 4/26/2022