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Ancef (Cefazolin Sodium) - Description and Clinical Pharmacology

 
 



ANCEF®
(cefazolin for injection)

DESCRIPTION

ANCEF is a semi-synthetic cephalosporin for parenteral administration. It is the sodium salt of 3-{[(5-methyl-1,3,4-thiadiazol-2-yl)thio]-methyl}-8-oxo-7-[2-(1H-tetrazol-1-yl)acetamido]-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid.

Structural Formula:

Each vial contains 48 mg of sodium/1 gram of cefazolin sodium.

ANCEF in lyophilized form is supplied in vials equivalent to 1 gram of cefazolin; in “Piggyback” Vials for intravenous admixture equivalent to 1 gram of cefazolin; and in Pharmacy Bulk Vials equivalent to 10 grams of cefazolin.

CLINICAL PHARMACOLOGY

After intramuscular administration of ANCEF to normal volunteers, the mean serum concentrations were 37 mcg/mL at 1 hour and 3 mcg/mL at 8 hours following a 500-mg dose, and 64 mcg/mL at 1 hour and 7 mcg/mL at 8 hours following a 1-gram dose.

Studies have shown that following intravenous administration of ANCEF to normal volunteers, mean serum concentrations peaked at approximately 185 mcg/mL and were approximately 4 mcg/mL at 8 hours for a 1-gram dose.

The serum half-life for ANCEF is approximately 1.8 hours following IV administration and approximately 2.0 hours following IM administration.

In a study (using normal volunteers) of constant intravenous infusion with dosages of 3.5 mg/kg for 1 hour (approximately 250 mg) and 1.5 mg/kg the next 2 hours (approximately 100 mg), ANCEF produced a steady serum level at the third hour of approximately 28 mcg/mL.

Studies in patients hospitalized with infections indicate that ANCEF produces mean peak serum levels approximately equivalent to those seen in normal volunteers.

Bile levels in patients without obstructive biliary disease can reach or exceed serum levels by up to 5 times; however, in patients with obstructive biliary disease, bile levels of ANCEF are considerably lower than serum levels (<1.0 mcg/mL).

In synovial fluid, the level of ANCEF becomes comparable to that reached in serum at about 4 hours after drug administration.

Studies of cord blood show prompt transfer of ANCEF across the placenta. ANCEF is present in very low concentrations in the milk of nursing mothers.

ANCEF is excreted unchanged in the urine. In the first 6 hours approximately 60% of the drug is excreted in the urine and this increases to 70% to 80% within 24 hours. ANCEF achieves peak urine concentrations of approximately 2,400 mcg/mL and 4,000 mcg/mL respectively following 500-mg and 1-gram intramuscular doses.

In patients undergoing peritoneal dialysis (2 L/hr.), ANCEF produced mean serum levels of approximately 10 and 30 mcg/mL after 24 hours’ instillation of a dialyzing solution containing 50 mg/L and 150 mg/L, respectively. Mean peak levels were 29 mcg/mL (range 13 to 44 mcg/mL) with 50 mg/L (3 patients), and 72 mcg/mL (range 26 to 142 mcg/mL) with 150 mg/L (6 patients). Intraperitoneal administration of ANCEF is usually well tolerated.

Controlled studies on adult normal volunteers, receiving 1 gram 4 times a day for 10 days, monitoring CBC, SGOT, SGPT, bilirubin, alkaline phosphatase, BUN, creatinine, and urinalysis, indicated no clinically significant changes attributed to ANCEF.

Microbiology

In vitro tests demonstrate that the bactericidal action of cephalosporins results from inhibition of cell wall synthesis. Cefazolin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in INDICATIONS AND USAGE.

Gram-Positive Aerobes

Staphylococcus aureus (including β-lactamase−producing strains)

Staphylococcus epidermidis

Streptococcus pyogenes, Streptococcus agalactiae, and other strains of streptococci

Streptococcus pneumoniae

Methicillin-resistant staphylococci are uniformly resistant to cefazolin, and many strains of enterococci are resistant.

Gram-Negative Aerobes

Escherichia coli

Proteus mirabilis

Most strains of indole positive Proteus (Proteus vulgaris), Enterobacter spp., Morganella morganii, Providencia rettgeri, Serratia spp., and Pseudomonas spp. are resistant to cefazolin.

Susceptibility Tests

Diffusion Techniques

Quantitative methods that require measurement of zone diameters provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure1 that has been recommended for use with disks to test the susceptibility of microorganisms to cefazolin uses the 30-mcg cefazolin disk. Results of the standardized single-disk susceptibility test1 with a 30-mcg cefazolin disk should be interpreted according to the following criteria:

RECOMMENDED RANGES FOR CEFAZOLIN SUSCEPTIBILITY TESTING

Zone Diameter (mm)

Interpretation

≥18

Susceptible (S)

15-17

Intermediate (I)

≤14

Resistant (R)

Standardized single-disk susceptibility test should be performed ONLY with a 30-mcg cefazolin disk.

A report of "Susceptible" indicates that the pathogen is likely to be inhibited by usually achievable concentrations of the antimicrobial compound in the blood. A report of "Intermediate" indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where high dosage of drug can be used. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of "Resistant" indicates that usually achievable concentrations of the antimicrobial compound in the blood are unlikely to be inhibitory and that other therapy should be selected.

Standardized susceptibility test procedures require the use of laboratory control microorganisms. The 30-mcg cefazolin disk should provide the following zone diameters in these laboratory test quality control strains:

Microorganism

Zone Diameter (mm)

E. coli

ATCC 25922

21-27

S. aureus

ATCC 25923

29-35

The cefazolin disk should not be used for testing susceptibility to other cephalosporins.

Dilution Techniques

Quantitative methods that are used to determine minimum inhibitory concentrations provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure uses a standardized dilution method2 (broth, agar, or microdilution) or equivalent with cefazolin powder. The MIC values obtained should be interpreted according to the following criteria:

MIC (mcg/mL)

Interpretation

≤16

Susceptible (S)

≥64

Resistant (R)

Interpretation should be as stated above for results using diffusion techniques.

As with standard diffusion techniques, dilution methods require the use of laboratory control microorganisms. Standard cefazolin powder should provide the following MIC values:

Microorganism

MIC (mcg/mL)

S. aureus

ATCC 25923

0.25-1.0

E. coli

ATCC 25922

1.0-4.0

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