CLINICAL PHARMACOLOGY
High plasma levels of cefotetan are attained after
intravenous administration of single doses to normal volunteers.
AFTER 1 GRAM IVa OR IM DOSE (mcg/mL) |
PLASMA CONCENTRATIONS |
Mean Plas ma Concentration |
Time After Injection |
Route |
15 min |
30 min |
1 h |
2 h |
4 h |
8 h |
12 h |
IV |
92 |
158 |
103 |
72 |
42 |
18 |
9 |
IM |
34 |
56 |
71 |
68 |
47 |
20 |
9 |
a 30-minute infusion |
AFTER 2 GRAM IVa OR IM DOSE (mcg/mL) |
PLASMA CONCENTRATIONS |
Mean Plas ma Concentration |
Time After Injection |
Route |
5 min |
10 min |
1 h |
3 h |
5 h |
9 h |
12 h |
IV |
237 |
223 |
135 |
74 |
48 |
22 |
12b |
IM |
- |
20 |
75 |
91 |
69 |
33 |
19 |
a Injected over 3 minutes
b Concentrations estimated from regression line |
The plasma elimination half-life of cefotetan is 3 to 4.6
hours after intravenous administration.
Repeated administration of cefotetan does not result in
accumulation of the drug in normal subjects.
Cefotetan is 88% plasma protein bound.
No active metabolites of cefotetan have been detected;
however, small amounts (less than 7%) of cefotetan in plasma and urine may be
converted to its tautomer, which has antimicrobial activity similar to the
parent drug.
In normal patients, from 51% to 81% of an administered
dose of cefotetan is excreted unchanged by the kidneys over a 24 hour period,
which results in high and prolonged urinary concentrations. Following intravenous
doses of 1 gram and 2 grams, urinary concentrations are highest during the
first hour and reach concentrations of approximately 1,700 and 3,500 mcg/mL,
respectively.
In volunteers with reduced renal function, the plasma
half-life of cefotetan is prolonged. The mean terminal half-life increases with
declining renal function, from approximately 4 hours in volunteers with normal
renal function to about 10 hours in those with moderate renal impairment. There
is a linear correlation between the systemic clearance of cefotetan and
creatinine clearance. When renal function is impaired, a reduced dosing
schedule based on creatinine clearance must be used (see DOSAGE AND ADMINISTRATION).
In pharmacokinetic studies of eight elderly patients
(greater than 65 years) with normal renal function and six healthy volunteers
(aged 25 to 28 years), mean (± 1 sd) Total Body Clearance (1.8 (0.1) L/h vs. 1.8
(0.3) L/h) and mean Volume of Distribution (10.4 (1.2) L vs. 10.3 (1.6) L) were
similar following administration of a one gram intravenous bolus dose.
Therapeutic levels of cefotetan are achieved in many body
tissues and fluids including:
skin |
ureter |
muscle |
bladder |
fat |
maxillary sinus mucosa |
myometrium |
tonsil |
endometrium |
bile |
cervix |
peritoneal fluid |
ovary |
umbilical cord serum |
kidney |
amniotic fluid |
Microbiology
The bactericidal action of cefotetan results from
inhibition of cell wall synthesis. Cefotetan has in vitro activity against a
wide range of aerobic and anaerobic gram-positive and gram-negative organisms.
The methoxy group in the 7-alpha position provides cefotetan with a high degree
of stability in the presence of beta-lactamases including both penicillinases
and cephalosporinase of gram-negative bacteria.
Cefotetan has been shown to be active against most
strains of the following organisms both in vitro and in clinical infections (see
INDICATIONS AND USAGE).
Gram-Negative Aerobes
Escherichia coli
Haemophilus influenzae (including
ampicillin-resistant strains)
Klebsiella species (including K. pneumoniae)
Morganella morganii
Neisseria gonorrhoeae (nonpenicillinase-producing
strains)
Proteus mirabilis
Proteus vulgaris
Providencia rettgeri
Serratia marcescens
NOTE: Approximately one-half of the usually clinically
significant strains of Enterobacter species (e.g., E. aerogenes and
E. cloacae) are resistant to cefotetan. Most strains of Pseudomonas
aeruginosa and Acinetobacter species are resistant to cefotetan.
Gram-Positive Aerobes
Staphylococcus aureus (including penicillinase-
and nonpenicillinase-producing strains)
Staphylococcus epidermidis
Streptococcus agalactiae (group B beta-hemolytic
streptococcus)
Streptococcus pneumoniae
Streptococcus pyogenes
NOTE: Methicillin-resistant staphylococci are resistant
to cephalosporins. Some strains of Staphylococcus epidermidis and most
strains of enterococci, e.g., Enterococcus faecalis (formerly Streptococcus
faecalis) are resistant to cefotetan.
Anaerobes
Prevotella bivia (formerly Bacteroides bivius)
Prevotella disiens (formerly Bacteroides disiens)
Bacteroides fragilis
Prevotella melaninogenica (formerly Bacteroides
melaninogenicus)
Bacteroides vulgatus
Fusobacterium species
Gram-positive bacilli (including Clostridium species; see
WARNINGS)
NOTE: Most strains of C. difficile are resistant
(see WARNINGS).
Peptococcus niger
Peptostreptococcus species
NOTE: Many strains of B. distasonis, B. ovatus
and B. thetaiotaomicron are resistant to cefotetan in vitro. However,
the therapeutic utility of cefotetan against these organisms cannot be
accurately predicted on the basis of in vitro susceptibility tests alone.
The following in vitro data are available but their
clinical significance is unknown. Cefotetan has been shown to be active in
vitro against most strains of the following organisms:
Gram-Negative Aerobes
Citrobacter species (including C. diversus and C.
freundii)
Klebsiella oxytoca
Moraxella (Branhamella) catarrhalis
Neisseria gonorrhoeae (penicillinase-producing
strains)
Salmonella species
Serratia species
Shigella species
Yersinia enterocolitica
Anaerobes
Porphyromonas asaccharolytica (formerly Bacteroides
asaccharolyticus)
Prevotella oralis (formerly Bacteroides oralis)
Bacteroides splanchnicus
Clostridium difficile (see WARNINGS)
Propionibacterium species
Veillonella species
Susceptibility Tests
Dilution Techniques
Quantitative methods are used to determine antimicrobial
minimal inhibitory concentrations (MICs).
These MICs provide estimates of the susceptibility of
bacteria to antimicrobial compounds. The MICs should be determined using a
standardized procedure. Standardized procedures are based on a dilution method1
(broth or agar) or equivalent with standardized inoculum concentrations and
standardized concentrations of cefotetan powder. The MIC values should be
interpreted according to the following criteria:
MIC (mcg/mL) |
Interpretation |
≤ 16 |
Susceptible (S) |
32 |
Intermediate (I) |
≥ 64 |
Resistant (R) |
A report of 'Susceptible' indicates that the pathogen is
likely to be inhibited if the antimicrobial compound in the blood reaches the
concentrations usually achievable. 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 which prevents
small uncontrolled technical factors from causing major discrepancies in
interpretation. A report of 'Resistant' indicates that the pathogen is not
likely to be inhibited if the antimicrobial compound in the blood reaches the
concentrations usually achievable; other therapy should be selected.
Standardized susceptibility test procedures require the
use of laboratory control microorganisms to control the technical aspects of
the laboratory procedures. Standard cefotetan powder should provide the
following MIC values:
Microorganism |
MIC (mcg/mL) |
E. coli ATCC 25922 |
0.06 to 0.25 |
S. aureus ATCC 29213 |
4 to 16 |
Diffusion Techniques
Quantitative methods that require measurement of zone
diameters also provide reproducible estimates of the susceptibility of bacteria
to antimicrobial compounds. One such standardized procedure2 requires
the use of the standardized inoculum concentrations. This procedure uses paper
disks impregnated with 30 mcg cefotetan to test the susceptibility of
microorganisms to cefotetan.
Reports from the laboratory providing results of the
standard single-disk susceptibility test with a 30 mcg cefotetan disk should be
interpreted according to the following criteria:
Zone Diameter (mm) |
Interpretation |
≥ 16 |
Susceptible (S) |
13 to 15 |
Intermediate (I) |
≤ 12 |
Resistant (R) |
Interpretation should be as stated above for results
using dilution techniques. Interpretation involves correlation of the diameter
obtained in the disk test with the MIC for cefotetan.
As with standardized dilution techniques, diffusion
methods require the use of laboratory control microorganisms that are used to
control the technical aspects of the laboratory procedures. For the diffusion
technique, the 30 mcg cefotetan disk should provide the following zone
diameters in these laboratory test quality control strains.
Microorganism |
Zone Diameter (mm) |
E. coli ATCC 25922 |
28 to 34 |
S. aureus ATCC 25923 |
17 to 23 |
Anaerobic Techniques
For anaerobic bacteria, the susceptibility to cefotetan
as MICs can be determined by standardized test methods3. The MIC
values obtained should be interpreted according to the following criteria:
MIC (mcg/mL) |
Interpretation |
≤ 16 |
Susceptible (S) |
32 |
Intermediate (I) |
≥ 64 |
Resistant (R) |
Interpretation is identical to that stated above for
results using dilution techniques.
As with other susceptibility techniques, the use of
laboratory control microorganisms is required to control the technical aspects
of the laboratory standardized procedures. Standardized cefotetan powder should
provide the following MIC values:
Microorganism |
MIC (mcg/mL) |
Bacteroides fragilis ATCC 25285 |
4 to 16 |
Bacteroides thetaiotaomicron ATCC 29741 |
32 to 128 |
Eubacterium lentum ATCC 43055 |
32 to 128 |
REFERENCES
1. National Committee for Clinical Laboratory Standards.
Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow
Aerobically - Third Edition. Approved Standard NCCLS Document M7-A3, Vol. 13,
No. 25, NCCLS, Villanova, PA, December 1993.
2. National Committee for Clinical Laboratory Standards.
Performance Standards for Antimicrobial Disk Susceptibility Tests - Fifth
Edition. Approved Standard NCCLS Document M2-A5, Vol. 13, No. 24, NCCLS,
Villanova, PA, December 1993.
3. National Committee for Clinical Laboratory Standards.
Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria - Third
Edition. Approved Standard NCCLS Document M11-A3, Vol. 13, No. 26, NCCLS,
Villanova, PA, December 1993.