Amoxicillin and clavulanate potassium are well absorbed from the
gastrointestinal tract after oral administration of AUGMENTIN. Dosing in the
fasted or fed state has minimal effect on the pharmacokinetics of amoxicillin.
While AUGMENTIN can be given without regard to meals, absorption of clavulanate
potassium when taken with food is greater relative to the fasted state. In 1
study, the relative bioavailability of clavulanate was reduced when AUGMENTIN
was dosed at 30 and 150 minutes after the start of a high-fat breakfast. The
safety and efficacy of AUGMENTIN have been established in clinical trials where
AUGMENTIN was taken without regard to meals.
Meana amoxicillin and clavulanate potassium
pharmacokinetic parameters are shown in the table below:
| Doseb and regimen | AUC0-24 (mcg•hr/mL) | Cmax (mcg/mL) |
amoxicillin/ clavulanate potassium | amoxicillin (±S.D.) | clavulanate potassium
(±S.D.) | amoxicillin (±S.D.) | clavulanate potassium
(±S.D.) |
| 250/125 mg q8h | 26.7 ± 4.56 | 12.6 ± 3.25 | 3.3 ± 1.12 | 1.5 ± 0.70 |
| 500/125 mg q12h | 33.4 ± 6.76 | 8.6 ± 1.95 | 6.5 ± 1.41 | 1.8 ± 0.61 |
| 500/125 mg q8h | 53.4 ± 8.87 | 15.7 ± 3.86 | 7.2 ± 2.26 | 2.4 ± 0.83 |
| 875/125 mg q12h | 53.5 ± 12.31 | 10.2 ± 3.04 | 11.6 ± 2.78 | 2.2 ±
0.99 |
a Mean values of 14 normal volunteers (n = 15 for
clavulanate potassium in the low-dose regimens). Peak concentrations occurred
approximately 1.5 hours after the dose.
b Administered at the start of a light meal.
Amoxicillin serum concentrations achieved with AUGMENTIN are similar to those
produced by the oral administration of equivalent doses of amoxicillin alone.
The half-life of amoxicillin after the oral administration of AUGMENTIN is 1.3
hours and that of clavulanic acid is 1.0 hour.
Approximately 50% to 70% of the amoxicillin and approximately 25% to 40% of
the clavulanic acid are excreted unchanged in urine during the first 6 hours
after administration of a single 250-mg or 500-mg tablet of AUGMENTIN.
Concurrent administration of probenecid delays amoxicillin excretion but does
not delay renal excretion of clavulanic acid.
Neither component in AUGMENTIN is highly protein-bound; clavulanic acid has
been found to be approximately 25% bound to human serum and amoxicillin
approximately 18% bound.
Amoxicillin diffuses readily into most body tissues and fluids with the
exception of the brain and spinal fluid. The results of experiments involving
the administration of clavulanic acid to animals suggest that this compound,
like amoxicillin, is well distributed in body tissues.
Microbiology
Amoxicillin is a semisynthetic antibiotic with a broad spectrum
of bactericidal activity against many gram-positive and gram-negative
microorganisms. Amoxicillin is, however, susceptible to degradation by
β-lactamases, and therefore, the spectrum of activity does not include organisms
which produce these enzymes. Clavulanic acid is a β-lactam, structurally related
to the penicillins, which possesses the ability to inactivate a wide range of
β-lactamase enzymes commonly found in microorganisms resistant to penicillins
and cephalosporins. In particular, it has good activity against the clinically
important plasmid-mediated β-lactamases frequently responsible for transferred
drug resistance.
The formulation of amoxicillin and clavulanic acid in AUGMENTIN protects
amoxicillin from degradation by β-lactamase enzymes and effectively extends the
antibiotic spectrum of amoxicillin to include many bacteria normally resistant
to amoxicillin and other β-lactam antibiotics. Thus, AUGMENTIN possesses the
properties of a broad-spectrum antibiotic and a β-lactamase inhibitor.
Amoxicillin/clavulanic acid 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
AerobesStaphylococcus aureus (β-lactamase and
non−β-lactamase−producing)c
c Staphylococci which are resistant to
methicillin/oxacillin must be considered resistant to amoxicillin/clavulanic
acid.
Gram-Negative
AerobesEnterobacter species (Although most
strains of Enterobacter species are resistant in
vitro, clinical efficacy has been demonstrated with AUGMENTIN in urinary tract
infections caused by these organisms.)
Escherichia coli (β-lactamase and
non−β-lactamase−producing)
Haemophilus influenzae (β-lactamase and
non−β-lactamase−producing)
Klebsiella species (All known strains are
β-lactamase−producing.)
Moraxella catarrhalis (β-lactamase and
non−β-lactamase−producing)
The following in vitro data are available, but their clinical significance is unknown.
Amoxicillin/clavulanic acid exhibits in vitro minimal inhibitory
concentrations (MICs) of 2 mcg/mL or less against most (≥ 90%) strains of Streptococcus pneumoniae d; MICs of
0.06 mcg/mL or less against most (≥ 90%) strains of Neisseria gonorrhoeae ; MICs of 4 mcg/mL or less against
most (≥ 90%) strains of staphylococci and anaerobic bacteria; and MICs of
8 mcg/mL or less against most (≥ 90%) strains of other listed organisms.
However, with the exception of organisms shown to respond to amoxicillin alone,
the safety and effectiveness of amoxicillin/clavulanic acid in treating clinical
infections due to these microorganisms have not been established in adequate and
well-controlled clinical trials.
d Because amoxicillin has greater in vitro activity
against S. pneumoniae than does ampicillin or
penicillin, the majority of S. pneumoniae strains
with intermediate susceptibility to ampicillin or penicillin are fully
susceptible to amoxicillin.
Gram-Positive
AerobesEnterococcus faecalise
Staphylococcus epidermidis (β-lactamase and
non−β-lactamase−producing)
Staphylococcus saprophyticus (β-lactamase and
non−β-lactamase−producing)
Streptococcus pneumoniaee f
Streptococcus pyogenese f
viridans group Streptococcuse
f
Gram-Negative
AerobesEikenella corrodens (β-lactamase and
non−β-lactamase−producing)
Neisseria gonorrhoeaee
(β-lactamase and non–β-lactamase–producing)
Proteus mirabilise
(β-lactamase and non–β-lactamase–producing)
Anaerobic
BacteriaBacteroides species, including Bacteroides fragilis (β-lactamase and
non–β-lactamase–producing)
Fusobacterium species (β-lactamase and
non–β-lactamase–producing)
Peptostreptococcus speciesf
e Adequate and well-controlled clinical trials have
established the effectiveness of amoxicillin alone in treating certain clinical
infections due to these organisms.
f These are non–β-lactamase−producing organisms, and
therefore, are susceptible to amoxicillin alone.
Susceptibility Testing
Dilution
TechniquesQuantitative methods are used to determine antimicrobial 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 amoxicillin/clavulanate potassium powder.
The recommended dilution pattern utilizes a constant amoxicillin/clavulanate
potassium ratio of 2 to 1 in all tubes with varying amounts of amoxicillin. MICs
are expressed in terms of the amoxicillin concentration in the presence of
clavulanic acid at a constant 2 parts amoxicillin to 1 part clavulanic acid. The
MIC values should be interpreted according to the following criteria:
RECOMMENDED RANGES FOR AMOXICILLIN/CLAVULANIC ACID SUSCEPTIBILITY TESTING
For Gram-Negative Enteric Aerobes:
| MIC
(mcg/mL) | Interpretation |
| ≤ 8/4 | Susceptible (S) |
| 16/8 | Intermediate (I) |
| ≥ 32/16 | Resistant
(R) |
For Staphylococcusg and Haemophilus species:
| MIC
(mcg/mL) | Interpretation |
| ≤ 4/2 | Susceptible (S) |
| ≥ 8/4 | Resistant
(R) |
g Staphylococci which are susceptible to
amoxicillin/clavulanic acid but resistant to methicillin/oxacillin must be
considered as resistant.
For S. pneumoniae from
non-meningitis sources:
Isolates should be tested using amoxicillin/clavulanic acid and the following
criteria should be used:
| MIC
(mcg/mL) | Interpretation |
| ≤ 2/1 | Susceptible (S) |
| 4/2 | Intermediate (I) |
| ≥ 8/4 | Resistant
(R) |
NOTE: These interpretive criteria are based on the
recommended doses for respiratory tract infections.
A report of “Susceptible” indicates that the pathogen is likely to be
inhibited if the antimicrobial compound in the blood reaches the concentration
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 amoxicillin/clavulanate potassium powder should provide the
following MIC values:
| Microorganism | MIC Range (mcg/mL)h |
| Escherichia coli ATCC
25922 | 2 to 8 |
| Escherichia coli ATCC
35218 | 4 to 16 |
| Enterococcus faecalis ATCC
29212 | 0.25 to 1.0 |
| Haemophilus influenzae ATCC
49247 | 2 to 16 |
| Staphylococcus aureus ATCC
29213 | 0.12 to 0.5 |
| Streptococcus
pneumoniae ATCC 49619 | 0.03 to 0.12 |
h Expressed as concentration of amoxicillin in the
presence of clavulanic acid at a constant 2 parts amoxicillin to 1 part
clavulanic acid.
Diffusion
TechniquesQuantitative 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 standardized inoculum concentrations. This procedure uses
paper disks impregnated with 30 mcg of amoxicillin/clavulanate potassium (20 mcg
amoxicillin plus 10 mcg clavulanate potassium) to test the susceptibility of
microorganisms to amoxicillin/clavulanic acid.
Reports from the laboratory providing results of the standard single-disk
susceptibility test with a 30-mcg amoxicillin/clavulanate acid (20 mcg
amoxicillin plus 10 mcg clavulanate potassium) disk should be interpreted
according to the following criteria: RECOMMENDED RANGES FOR
AMOXICILLIN/CLAVULANIC ACID SUSCEPTIBILITY TESTING
For Staphylococcusi species and H. influenzaej:
| Zone Diameter
(mm) | Interpretation |
| ≥ 20 | Susceptible (S) |
| ≤ 19 | Resistant
(R) |
For Other Organisms Except S.
pneumoniaek and N.
gonorrhoeael:
| Zone Diameter
(mm) | Interpretation |
| ≥ 18 | Susceptible (S) |
| 14 to 17 | Intermediate (I) |
| ≤ 13 | Resistant
(R) |
i Staphylococci which are resistant to
methicillin/oxacillin must be considered as resistant to amoxicillin/clavulanic
acid.
j A broth microdilution method should be used for
testing H. influenzae. Beta-lactamase−negative,
ampicillin-resistant strains must be considered resistant to
amoxicillin/clavulanic acid.
k Susceptibility of S.
pneumoniae should be determined using a 1-mcg oxacillin disk. Isolates
with oxacillin zone sizes of ≥2 0 mm are susceptible to amoxicillin/clavulanic
acid. An amoxicillin/clavulanic acid MIC should be determined on isolates of
S. pneumoniae with oxacillin zone sizes of ≤1
9 mm.
l A broth microdilution method should be used for
testing N. gonorrhoeae and interpreted according to
penicillin breakpoints.
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 amoxicillin/clavulanic acid.
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
amoxicillin/clavulanate potassium (20-mcg amoxicillin plus 10-mcg clavulanate
potassium) disk should provide the following zone diameters in these laboratory
quality control strains:
| Microorganism | Zone Diameter
(mm) |
| Escherichia coli ATCC
25922 | 19 to 25 |
| Escherichia coli ATCC
35218 | 18 to 22 |
| Staphylococcus
aureus ATCC 25923 | 28 to 36 |