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Cefadroxil

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Cefadroxil

Cefadroxil

CLINICAL PHARMACOLOGY

Cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) is rapidly absorbed after oral administration. Following single doses of 500 and 1000 mg, average peak serum concentrations were approximately 16 and 28 mcg/mL, respectively. Measurable levels were present 12 hours after administration. Over 90% of the drug is excreted unchanged in the urine within 24 hours. Peak urine concentrations are approximately 1800 mcg/mL during the period following a single 500 mg oral dose. Increases in dosage generally produce a proportionate increase in cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) urinary concentration. The urine antibiotic concentration, following a 1-g dose, was maintained well above the MIC of susceptible urinary pathogens for 20 to 22 hours.

Microbiology

In vitro tests demonstrate that the cephalosporins are bactericidal because of their inhibition of cell-wall synthesis. Cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) has been shown to be active against the following organisms both in vitro and in clinical infections (see INDICATIONS AND USAGE):

Beta-hemolytic streptococci

Staphylococci, including penicillinase-producing strains

Streptococcus (Diplococcus) pneumoniae

Escherichia coli

Proteus mirabilis

Klebsiella species

Moraxella (Branhamella) catarrhalis

Note: Most strains of Enterococcus faecalis (formerly Streptococcus faecalis) and Enterococcus faecium (formerly Streptococcus faecium) are resistant to cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) . It is not active against most strains of Enterobacter species, Morganella morganii (formerly Proteus morganii), and P. vulgaris. It has no activity against Pseudomonas species and Acinetobacter calcoaceticus (formerly MimaandHerella species).

Susceptibility tests: Diffusion techniques

The use of antibiotic disk susceptibility test methods which measure zone diameter give an accurate estimation of antibiotic susceptibility. One such standard procedure1 which has been recommended for use with disks to test susceptibility of organisms to cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) uses the cephalosporin class (cephalothin) disk. Interpretation involves the correlation of the diameters obtained in the disk test with the minimum inhibitory concentration (MIC) for cefadroxil (cefadroxil (cefadroxil hemihydrate) hemihydrate) .

Reports from the laboratory giving results of the standard single-disk susceptibility test with a 30 mcg cephalothin disk should be interpreted according to the following criteria:


Zone Diameter Interpretation
(mm)
≥18 (S) Susceptible
15 to 17 (I) Intermediate
≤14 (R) Resistant (R) Resistant

A report of “;Susceptible” indicates that the pathogen is likely to be inhibited by generally achievable blood levels. A report of “intermediate susceptibility” suggests that the organism would be susceptible if high dosage is used or if the infection is confined to tissue and fluids (e.g., urine) in which high antibiotic levels are attained. A report of “Resistant” indicates that achievable concentrations of the antibiotic are unlikely to be inhibitory and other therapy should be selected.

Standardized procedures require the use of laboratory control organisms. The 30 mcg cephalothin disk should give the following zone diameters:


Organism Zone Diameter
(mm)
Staphylococcus aureus ATCC 25923 29 to 37
Escherichia coli ATCC 25922 17 to 22

Dilution Techniques

When using the NCCLS agar dilution or broth dilution (including microdilution) method2 or equivalent, a bacterial isolate may be considered susceptible if the MIC (minimum inhibitory concentration) value for cephalothin is 8 mcg/mL or less. Organisms are considered resistant if the MIC is 32 mcg/mL or greater. Organisms with an MIC value of less than 32 mcg/mL but greater than 8 mcg/mL are intermediate.

As with standard diffusion methods, dilution procedures require the use of laboratory control organisms. Standard cephalothin powder should give MIC values in the range of 0.12 mcg/mL and 0.5 mcg/mL for Staphylococcus aureus ATCC 29213. For Escherichia coli ATCC 25922, the MIC range should be between 4 mcg/mL and 16 mcg/mL. For Streptococcus faecalis ATCC 29212, the MIC range should be between 8 and 32 mcg/mL.

REFERENCES

1. National Committee for Clinical Laboratory Standards, Approved Standard, Performance Standards for Antimicrobial Disk Susceptibility Test, 4th Edition, Vol. 10(7): M2-A4, Villanova, PA, April, 1990.

2. National Committee for Clinical Laboratory Standards, Approved Standard: Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically, 2nd Edition, Vol. 10(8): M7-A2, Villanova, PA, April, 1990.

Last reviewed on RxList: 7/31/2007
This monograph has been modified to include the generic and brand name in many instances.

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