Amoxicillin and clavulanate potassium are well absorbed from the
gastrointestinal tract after oral administration of amoxicillin and clavulanate
potassium. Dosing in the fasted or fed state has minimal effect on the
pharmacokinetics of amoxicillin. While amoxicillin and clavulanate potassium 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 amoxicillin and clavulanate
potassium was dosed at 30 and 150 minutes after the start of a high-fat
breakfast. The safety and efficacy of amoxicillin and clavulanate potassium have
been established in clinical trials where amoxicillin and clavulanate potassium
was taken without regard to meals.
Oral administration of single doses of amoxicillin and clavulanate potassium
for oral suspension 200 mg/5 mL and 400 mg/5 mL, and amoxicillin and clavulanate
potassium tablets (chewable) 200 mg/28.5 mg and 400 mg/57 mg) to 28 adult
volunteers yielded comparable pharmacokinetic data:
| Dose* | AUC0-∞(mcg.hr/mL) | Cmax (mcg/mL)† |
| (amoxicillin/clavulanate
potassium) | amoxicillin(± S.D.) | clavulanate potassium(± S.D.) | amoxicillin(± S.D.) | clavulanate potassium(± S.D.) |
| 400 mg/57 mg (5 mL of suspension) | 17.29 ± 2.28 | 2.34 ± 0.94 | 6.94 ± 1.24 | 1.10 ± 0.42 |
| 400 mg/57 mg (one chewable tablet) | 17.24 ± 2.64 | 2.17 ± 0.73 | 6.67 ± 1.37 | 1.03 ± 0.33 |
*Administered at the start of a light meal.
†Mean values of 28 normal volunteers. Peak
concentrations occurred approximately 1 hour after the dose.
Oral administration of 5 mL of amoxicillin and clavulanate potassium 250 mg/5
mL suspension or the equivalent dose of 10 mL amoxicillin and clavulanate
potassium 125 mg/5 mL suspension provides average peak serum concentrations
approximately 1 hour after dosing of 6.9 mcg/mL for amoxicillin and 1.6 mcg/mL
for clavulanic acid. The areas under the serum concentration curves obtained
during the first 4 hours after dosing were 12.6 mcg.hr/mL for amoxicillin and
2.9 mcg.hr/mL for clavulanic acid when 5 mL of amoxicillin and clavulanate
potassium 250 mg/5 mL suspension or equivalent dose of 10 mL of amoxicillin and
clavulanate potassium 125 mg/5 mL suspension was administered to adult
volunteers. One amoxicillin and clavulanate potassium 250 mg chewable tablet or
two amoxicillin and clavulanate potassium125 mg chewable tablets are equivalent
to 5 mL of amoxicillin and clavulanate potassium 250 mg/5 mL suspension and
provide similar serum levels of amoxicillin and clavulanic acid.
Amoxicillin serum concentrations achieved with amoxicillin and clavulanate
potassium 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 amoxicillin and clavulanate potassium is 1.3 hours and that of
clavulanic acid is 1 hour. Time above the minimum inhibitory concentration of 1
mcg/mL for amoxicillin has been shown to be similar after corresponding q12h and
q8h dosing regimens of amoxicillin and clavulanate potassium in adults and
children. 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 10 mL of amoxicillin and clavulanate potassium 250
mg/5 mL suspension.
Concurrent administration of probenecid delays amoxicillin excretion but does
not delay renal excretion of clavulanic acid.
Neither component in amoxicillin and clavulanate potassium 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.
Two hours after oral administration of a single 35 mg/kg dose of amoxicillin
and clavulanate potassium suspension to fasting children, average concentrations
of 3 mcg/mL of amoxicillin and 0.5 mcg/mL of clavulanic acid were detected in
middle ear effusions.
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 amoxicillin and
clavulanate potassium 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, amoxicillin and clavulanate potassium possess the distinctive
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 the INDICATIONS AND
USAGE.
Gram-Positive Aerobes:
Staphylococcus aureus(β-lactamase and
non-β-lactamase-producing)§
§ Staphylococci which are
resistant to methicillin/oxacillin must be considered resistant to
amoxicillin/clavulanic acid.
Gram-Negative Aerobes:
Enterobacterspecies (Although most strains of
Enterobacter species are resistant in vitro, clinical efficacy has been demonstrated with
amoxicillin and clavulanate potassium 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)
Klebsiellaspecies (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 0.5 mcg/mL or less against most (≥
90%) strains of Streptococcus pneumoniae║; 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.
║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 Aerobes:
Enterococcus faecalis¶
Staphylococcus epidermidis (β-lactamase and
non-β-lactamase-producing)
Staphylococcus saprophyticus (β-lactamase and
non-β-lactamase-producing)
Streptococcus pneumoniae¶**
Streptococcus pyogenes¶**
viridans group Streptococcus ¶**
Gram-Negative Aerobes:
Eikenella corrodens(β-lactamase and
non-β-lactamase-producing)
Neisseria gonorrhoeae¶(β-lactamase and non-β-lactamase-producing)
Proteus mirabilis¶(β-lactamase and non-β-lactamase-producing)
Anaerobic Bacteria:
Bacteroidesspecies, including Bacteroides fragilis (β-lactamase and
non-β-lactamase-producing)
Fusobacteriumspecies (β-lactamase and
non-β-lactamase-producing)
Peptostreptococcusspecies **
¶ Adequate and well-controlled clinical trials have
established the effectiveness of amoxicillin alone in treating certain clinical
infections due to these organisms.
**These are non-β-producing
organisms, and therefore, are susceptible to amoxicillin alone.
Susceptibility Testing:Dilution Techniques: Quantitative 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 method
1 (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 to1 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 Staphylococcus†† and Haemophilus species:
| MIC (mcg/mL) | Interpretation | |
| ≤ 4/2 | Susceptible | (S) |
| ≥ 8/4 | Resistant | (R) |
††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 that 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)‡‡ |
| E. coli ATCC 25922 | 2 to 8 |
| E. coli ATCC 35218 | 4 to 16 |
| E. faecalis ATCC 29212
| 0.25 to 1 |
| H. influenzae ATCC 49247
| 2 to 16 |
| S. aureus ATCC 29213 | 0.12 to 0.5 |
| S. pneumoniae ATCC 49619
| 0.03 to 0.12 |
‡‡Expressed as concentration
of amoxicillin in the presence of clavulanic acid at a constant 2 parts
amoxicillin to 1 part clavulanic acid.
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 procedure 2 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 potassium (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 Staphylococcus§§ species and H.influenzae
a: | Zone Diameter
(mm) | Interpretation | |
| ≥ 20 | Susceptible | (S) |
| ≤ 19 | Resistant | (R) |
For Other Organisms Except S. pneumoniaeb and N.
gonorrhoeaec: | Zone Diameter
(mm) | Interpretation | |
| ≥ 18 | Susceptible | (S) |
| 14 to 17 | Intermediate | (I) |
| ≤ 13 | Resistant | (R) |
§§Staphylococci which are
resistant to methicillin/oxacillin must be considered as resistant to
amoxicillin/clavulanic acid.
aA broth microdilution method should be used for
testing H. influenzae. Beta-lactamase-negative,
ampicillin-resistant strains must be considered resistant to
amoxicillin/clavulanic acid.
bSusceptibility of S.
pneumoniae should be determined using a 1 mcg oxacillin disk. Isolates
with oxacillin zone sizes of ≥ 20 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 ≤ 19
mm.
cA 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) |
| E. coli ATCC 25922 | 19 to 25 mm |
| E. coli ATCC 35218 | 18 to 22 mm |
| S. aureus ATCC 25923 | 28 to 36 mm |