Amoxicillin and clavulanate potassium are well absorbed from the
gastrointestinal tract after oral administration of AUGMENTIN XR.
AUGMENTIN XR is an extended-release formulation which provides sustained
plasma concentrations of amoxicillin. Amoxicillin systemic exposure achieved
with AUGMENTIN XR is similar to that produced by the oral administration of
equivalent doses of amoxicillin alone. In a study of healthy adult volunteers,
the pharmacokinetics of AUGMENTIN XR were compared when administered in a fasted
state, at the start of a standardized meal (612 kcal, 89.3 g carb, 24.9 g fat,
and 14.0 g protein), or 30 minutes after a high-fat meal. When the systemic
exposure to both amoxicillin and clavulanate is taken into consideration,
AUGMENTIN XR is optimally administered at the start of a standardized meal.
Absorption of amoxicillin is decreased in the fasted state. AUGMENTIN XR is not
recommended to be taken with a high-fat meal, because clavulanate absorption is
decreased. The pharmacokinetics of the components of AUGMENTIN XR following
administration of two AUGMENTIN XR tablets at the start of a standardized meal
are presented in Table 1.
Table 1. Mean (SD) Pharmacokinetic Parameters for Amoxicillin and
Clavulanate Following Oral Administration of Two AUGMENTIN XR Tablets
(2,000 mg/125 mg) to Healthy Adult Volunteers (n = 55) Fed a Standardized
Meal| Parameter (units) | Amoxicillin | Clavulanate |
| AUC(0-inf) (mcg•hr/mL) | 71.6 (16.5) | 5.29 (1.55) |
| Cmax
(mcg/mL) | 17.0 (4.0) | 2.05 (0.80) |
| Tmax
(hours)a | 1.50 (1.00 - 6.00) | 1.03 (0.75 - 3.00) |
| T½
(hours) | 1.27 (0.20) | 1.03
(0.17) |
a Median (range).
The half-life of amoxicillin after the oral administration of AUGMENTIN XR is
approximately 1.3 hours, and that of clavulanate is approximately 1.0 hour.
Clearance of amoxicillin is predominantly renal, with approximately 60% to
80% of the dose being excreted unchanged in urine, whereas clearance of
clavulanate has both a renal (30% to 50%) and a non-renal component.
Concurrent administration of probenecid delays amoxicillin excretion but does
not delay renal excretion of clavulanate.
In a study of adults, the pharmacokinetics of amoxicillin and clavulanate
were not affected by administration of an antacid (MAALOX®), either simultaneously with or 2 hours after AUGMENTIN
XR.
Neither component in AUGMENTIN XR is highly protein-bound; clavulanate 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.
In a study of pediatric patients with acute bacterial sinusitis, 7 to 15
years of age, and weighing at least 40 kg, the pharmacokinetics of amoxicillin
and clavulanate were assessed following administration of AUGMENTIN XR
2000 mg/125 mg (as two 1000 mg/62.5 mg tablets) every 12 hours with food
(Table 2).
Table 2. Mean (SD) Pharmacokinetic Parameters for Amoxicillin and
Clavulanate Following Oral Administration of Two AUGMENTIN XR Tablets
(2,000 mg/125 mg) Every 12 Hours With Food to Pediatric Patients (7 to 15 Years
of Age and Weighing ≥ 40kg) With Acute Bacterial Sinusitis| Parameter (units) | Amoxicillin (n=24) | Clavulanate (n=23) |
| AUC(0-τ) (mcg•hr/mL) | 57.8 (15.6) | 3.18 (1.37) |
| Cmax
(mcg/mL) | 11.0 (3.34) | 1.17 (0.67) |
| Tmax
(hours)a | 2.0 (1.0 – 5.0) | 2.0 (1.0 – 4.0) |
| T½ (hours) | 3.32 (2.21)b | 0.94 (0.13)c |
a Median (range).
b n=18.
c n=17.
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, its spectrum of activity does not include organisms
which produce these enzymes. Clavulanic acid is a β-lactam, structurally related
to penicillin, 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 found responsible for
transferred drug resistance.
The clavulanic acid component of AUGMENTIN XR 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.
Amoxicillin/clavulanic acid has been shown to be active against most isolates
of the following microorganisms, both in vitro and in clinical infections as
described in the INDICATIONS AND USAGE section.
Aerobic
Gram-Positive MicroorganismsStreptococcus pneumoniae (including
isolates with penicillin MICs ≤ 2 mcg/mL)
Staphylococcus aureus (including
β-lactamase−producing isolates)
NOTE: Staphylococci which are resistant to
methicillin/oxacillin must be considered resistant to amoxicillin/clavulanic
acid.
Aerobic
Gram-Negative MicroorganismsHaemophilus influenzae (including
β-lactamase−producing isolates)
Moraxella catarrhalis (including
β-lactamase−producing isolates)
Haemophilus parainfluenzae (including
β-lactamase−producing isolates)
Klebsiella pneumoniae (all known isolates are
β-lactamase−producing)
The following in vitro data are available, but their
clinical significance is unknown.
At least 90% of the following microorganisms exhibit in vitro minimum
inhibitory concentrations (MICs) less than or equal to the susceptible
breakpoint for amoxicillin/clavulanic acid.1,2 However,
the safety and efficacy of amoxicillin/clavulanic acid in treating infections
due to these microorganisms have not been established in adequate and
well-controlled trials.
Aerobic
Gram-Positive MicroorganismsStreptococcus pyogenes
Anaerobic
MicroorganismsBacteroides fragilis (including
β-lactamase−producing isolates)
Fusobacterium nucleatum (including
β-lactamase−producing isolates)
Peptostreptococcus magnus
Peptostreptococcus micros
NOTE:S. pyogenes, P. magnus, and P. micros do not
produce β-lactamase, and therefore, are susceptible to amoxicillin alone.
Adequate and well-controlled clinical trials have established the effectiveness
of amoxicillin alone in treating certain clinical infections due to S. pyogenes.
Susceptibility Test Methods
When available, the clinical microbiology laboratory should
provide cumulative results of in vitro susceptibility test results for
antimicrobial drugs used in local hospitals and practice areas to the physician
as periodic reports that describe the susceptibility profile of nosocomial and
community-acquired pathogens. These reports should aid the physician in
selecting the most effective antimicrobial.
Dilution
TechniqueQuantitative methods are used to determine antimicrobial minimum
inhibitory concentrations (MICs). These MICs provide estimates of the
susceptibility of bacteria to antimicrobial compounds. The MICs should be
determined using a standardized procedure.1,3
Standardized procedures are based on dilution methods (broth or agar; broth for
S. pneumoniae and H.
influenzae) or equivalent with standardized inoculum concentration 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 criteria provided in
Table 3.
Diffusion
TechniqueQuantitative methods that require measurement of zone diameters
also provide reproducible estimates of the susceptibility of bacteria to
antimicrobials. One such standardized technique requires the use of a
standardized inoculum concentration.1,4 This procedure
uses paper disks impregnated with 30 mcg amoxicillin/clavulanate potassium
(20 mcg amoxicillin plus 10 mcg clavulanate potassium) to test susceptibility of
microorganisms to amoxicillin/clavulanate potassium. Disk diffusion zone sizes
should be interpreted according to criteria provided in Table 3.
Table 3. Susceptibility Test Result Interpretive Criteria for
Amoxicillin/Clavulanate Potassium
| Minimum Inhibitory Concentration (mcg/mL) | Disk Diffusion (Zone
Diameter in mm) |
| Pathogen | S | I | R | S | I | R |
| Haemophilus spp. | ≤ 4/2 | Not applicable (NA) | ≥ 8/4 | ≥ 20 | NA | ≤ 19 |
| Klebsiella
pneumoniae | ≤ 8/4 | 16/8 | ≥ 32/16 | ≥ 18 | 14 to 17 | ≤ 13 |
| Staphylococcus spp. | ≤ 4/2 | NA | ≥ 8/4 | ≥ 20 | NA | ≤ 19 |
| Streptococcus pneumoniae | ≤ 2/1 | 4/2 | ≥ 8/4 | NA |
NOTE: Susceptibility of S.
pneumoniae should be determined using a 1-mcg oxacillin disk. Isolates
with oxacillin zone sizes of ≥ 20 mm are susceptible to amoxicillin/clavulanate
acid. An amoxicillin/clavulanate acid MIC should be determined on isolates of
S. pneumoniae with oxacillin zone sizes of ≤
19 mm.
NOTE: β-lactamase−negative, ampicillin-resistant
H. influenzae isolates must be considered resistant
to amoxicillin/clavulanic acid.
A report of S (“Susceptible”) indicates that the antimicrobial is likely to
inhibit growth of the pathogen if the antimicrobial compound in the blood
reaches the concentration usually achievable. A report of I (“Intermediate”)
indicates that the result should be considered equivocal, and, if the
microorganism is not fully susceptible to alternative, clinically feasible
antimicrobials, 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 doses of antimicrobial 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 R (“Resistant”) indicates that the antimicrobial is not likely to inhibit
growth of the pathogen if the antimicrobial compound in the blood reaches the
concentration usually achievable; other therapy should be selected.
Standardized susceptibility test procedures require the use of quality
control microorganisms to determine the performance of the test procedures.1,3,4 Standard amoxicillin/clavulanate potassium powder should
provide the MIC ranges for the quality control organisms in Table 4. For the
disk diffusion technique, the 30 mcg amoxicillin/clavulanate potassium disk
should provide the zone diameter ranges for the quality control organisms in
Table 4.
Table 4. Acceptable Quality Control Ranges for Amoxicillin/Clavulanate
Potassium| Quality Control Organism | Minimum
Inhibitory Concentration Range (mcg/mL) | Disk Diffusion (Zone
Diameter Range in mm) |
Escherichia coli ATCC®a 35218b (H.
influenzae quality control) | 4/2 to 16/8 | 17 to 22 |
| Escherichia coli ATCC 25922 | 2/1 to 8/4 | 18 to 24 |
| Haemophilus influenzae ATCC 49247 | 2/1 to 16/8 | 15 to 23 |
| Staphylococcus aureus ATCC 29213 | 0.12/0.06 to 0.5/0.25 | Not applicable (NA) |
| Staphylococcus aureus ATCC 25923 | NA | 28 to 36 |
| Streptococcus pneumoniae ATCC 49619 | 0.03/0.015 to 0.12/0.06 | NA |
a ATCC is a trademark of the American Type Culture
Collection.
b When using Haemophilus
Test Medium (HTM).