Absorption:
Amoxicillin is stable in the presence of gastric acid and
is rapidly absorbed after oral administration. The effect of food
on the absorption of amoxicillin from the tablets and suspension of
amoxicillin has been partially investigated; 400-mg and 875-mg
formulations have been studied only when administered at the start
of a light meal.
Orally administered doses of 250-mg and 500-mg amoxicillin
capsules result in average peak blood levels 1 to 2 hours after
administration in the range of 3.5 mcg/mL to 5.0 mcg/mL and 5.5
mcg/mL to 7.5 mcg/mL, respectively.
Mean amoxicillin pharmacokinetic parameters from an open,
two-part, single-dose crossover bioequivalence study in 27 adults
comparing 875 mg of amoxicillin with 875 mg of AUGMENTIN®
(amoxicillin/clavulanate potassium) showed that the 875-mg tablet
of amoxicillin produces an AUC0-∞ of 35.4
± 8.1 mcg∙hr/mL and a Cmax of 13.8
± 4.1 mcg/mL. Dosing was at the start of a light meal
following an overnight fast.
Orally administered doses of amoxicillin suspension, 125
mg/5 mL and 250 mg/5 mL, result in average peak blood levels 1 to 2
hours after administration in the range of 1.5 mcg/mL to 3.0 mcg/mL
and 3.5 mcg/mL to 5.0 mcg/mL, respectively.
Oral administration of single doses of 400-mg chewable
tablets and 400 mg/5 mL suspension of amoxicillin to 24 adult volunteers
yielded comparable pharmacokinetic data:
Table 3. Mean Pharmacokinetic Parameters of Amoxicillin
(400 mg chewable tablets and 400 mg/5 mL suspension) in Healthy
Adults| Dose* | AUC0-∞ (mcg∙hr/mL) | Cmax (mcg/mL)† |
|---|
| Amoxicillin | Amoxicillin (±S.D.) | Amoxicillin (±S.D.) |
| 400 mg (5 mL of suspension) | 17.1 (3.1) | 5.92 (1.62) |
| 400 mg (1 chewable tablet) | 17.9 (2.4) | 5.18 (1.64) |
*Administered at the start of a light
meal.
†Mean values of 24
normal volunteers. Peak concentrations occurred
approximately 1 hour after the dose.
Distribution:
Amoxicillin diffuses readily into most body tissues and fluids,
with the exception of brain and spinal fluid, except when meninges
are inflamed. In blood serum, amoxicillin is approximately 20%
protein-bound. Following a 1-gram dose and utilizing a special skin
window technique to determine levels of the antibiotic, it was
noted that therapeutic levels were found in the interstitial
fluid.
Metabolism and
Excretion: The half-life of amoxicillin is 61.3 minutes.
Approximately 60% of an orally administered dose of amoxicillin is
excreted in the urine within 6 to 8 hours. Detectable serum levels
are observed up to 8 hours after an orally administered dose of
amoxicillin. Since most of the amoxicillin is excreted unchanged in
the urine, its excretion can be delayed by concurrent
administration of probenecid [see DRUG INTERACTIONS (7.1)].
Mechanism of Action
Amoxicillin is similar to penicillin in its bactericidal
action against susceptible bacteria during the stage of active
multiplication. It acts through the inhibition of cell wall
biosynthesis that leads to the death of the bacteria.
Method of Resistance
Resistance to amoxicillin is mediated primarily through
enzymes called beta-lactamases that cleave the beta-lactam ring of
amoxicillin, rendering it inactive.
Amoxicillin has been shown to
be active against most isolates of the bacteria listed below, both
in vitro and in clinical infections as described in the INDICATIONS
AND USAGE section (1).
| Gram-Positive Bacteria | Gram-Negative Bacteria |
|---|
| Enterococcus
faecalis | Escherichia coli |
| Staphylococcus
spp. | Haemophilus
influenzae |
| Streptococcus
pneumoniae | Neisseria gonorrhoeae
|
|
Alpha and β-hemolytic streptococci
| Proteus mirabilis |
| Helicobacter pylori |
Susceptibility Test
Methods: (susceptibility to amoxicillin can be
determined using ampicillin powder and a 10 mcg ampicillin
disk)
When available, clinical microbiology should provide
the results of in vitro susceptibility test results for antimicrobial drugs
used in resident hospitals 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 an antimicrobial drug
product for treatment.
Dilution
Techniques: Quantitative 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. Standardized procedures are
based on dilution methods (broth or agar)2,3
or equivalent with standardized inoculum concentrations
and standardized concentrations of ampicillin powder.
The MIC values should be
interpreted according to the criteria in Table
4.
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 procedure3 requires the use of
standardized inoculum concentrations. This procedure
uses paper disks impregnated with 10 mcg ampicillin to
test the susceptibility of bacteria to ampicillin.
Interpretation involves correlation of the diameter
obtained in the disk test with the MIC for amoxicillin.
Reports from the laboratory providing results of the
standard single-disk susceptibility test with a 10 mcg
ampicillin disk should be interpreted according to the
criteria listed in Table 4.
Table 4. Susceptibility Test Interpretive Criteria for
Amoxicillin | Minimum Inhibitory Concentration
(mcg/mL) | Disk Diffusion (zone diameter in
mm) |
|---|
| Susceptible | Intermediate | Resistant | Susceptible | Intermediate | Resistant |
| Enterococcus spp. | ≤ 8 | - | ≥ 16 | ≥ 17 | - | ≤ 16 |
| Staphylococcus spp. | ≤ 0.25 | | ≥ 0.5 | ≥ 29 | | ≤ 28 |
Streptococci, viridians group (alpha-hemolytic streptococci) | ≤ 0.25 | 0.5 to 4 | ≥ 8 | - | - | - |
| β-hemolytic streptococci | ≤ 0.25 | - | - | ≥ 24 | - | - |
| Streptococcus
pneumoniae (non-meningitis
isolates)* | ≤ 2 | 4 | ≥ 8 | - | - | - |
| Enterobacteriaceae | ≤ 8 | 16 | ≥ 32 | ≥ 17 | 14 to 16 | ≤ 13 |
| Haemophilus
influenzae | ≤ 1 | 2 | ≥ 4 | ≥ 22 | 19 to 21 | ≤ 18 |
| Neisseria
gonorrhoeae** | - | - | - | - | - | - |
*S. pneumoniae
should be tested using a 1-mcg
oxacillin disk. Isolates with oxacillin
zone sizes of ≥ 20 mm are
susceptible to amoxicillin. An amoxicillin
MIC should be determined on isolates of
S.
pneumoniae with oxacillin zone
sizes of ≤ 19 mm.
** A positive beta lactamase test
indicates resistance to amoxicillin.
Isolates that are resistant to penicillin
by MIC testing are also expected to be
resistant to amoxicillin.
A report of “Susceptible” indicates the
pathogen is likely to be inhibited if the antimicrobial
compound in the blood reaches concentrations that are
usually achievable. A report of “Intermediate”
indicates that result should be considered equivocal,
and, if the microorganism is not fully susceptible to
alternative, clinically feasible drugs, the test should
be repeated. The intermediate 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. The intermediate
category also provides a buffer zone, which prevents
small uncontrolled technical factors from causing major
discrepancies in interpretation. A report of
“Resistant” indicates the pathogen is not likely to be
inhibited if the antimicrobial compound in the blood
reaches concentrations that are usually achievable and
other therapy(ies) are likely to be
preferred.
Quality
Control:
Susceptibility techniques require use of
laboratory control microorganisms to control the
technical aspects of the laboratory standardized
procedures.2,3,4 Standard ampicillin powder should
provide the MIC values described below. For the
diffusion technique using the 10-mcg ampicillin disk,
the criteria are provided in Table 5.
Table 5. Acceptable Quality Control
Ranges for Amoxicillin| Bacteria | ATCC# | MIC Range (mcg/mL) | Disc Diffusion Zone Range (mm) |
|---|
| Escherichia
coli | 25922 | 2 to 8 | 16 to 22 |
| Enterococcus
faecalis | 29212 | 0.5 to 2 | |
| Haemophilus
influenzae | 49247 | 2 to 8 | 13 to 21 |
| Staphylococcus
aureus | 29213 | 0.5 to 2 | |
| 25923 | | 27 to 35 |
| Streptococcus
pneumoniae | 49619 | 0.06 to 0.25 | |
# ATCC = American
Type Culture Collection
Susceptibility Testing
for Helicobacter
pylori : Amoxicillin in vitro susceptibility
testing methods for determining minimum inhibitory
concentrations (MICs) and zone sizes have not been
standardized, validated, or approved for testing H. pylori. Specimens for
H. pylori and
clarithromycin susceptibility test results should be obtained
on isolates from patients who fail triple therapy. If
clarithromycin resistance is found, a
non-clarithromycin-containing regimen should be
used.
Capsules: Each capsule of
amoxicillin, with royal blue opaque cap and pink opaque body, contains 250 mg
or 500 mg amoxicillin as the trihydrate. The cap and body of the 250-mg
capsule are imprinted with the product name AMOXIL and 250; the cap and
body of the 500 mg capsule are imprinted with AMOXIL and 500.
250-mg Capsule
NDC 43598-225-01: Bottles of 100
NDC 43598-225-05: Bottles of 500
500-mg Capsule
NDC 43598-205-01: Bottles of 100
NDC 43598-205-05: Bottles of 500
Tablets: Each tablet contains
500 mg or 875 mg amoxicillin as the trihydrate. Each film-coated,
capsule-shaped, pink tablet is debossed with AMOXIL centered over 500 or
875, respectively. The 875-mg tablet is scored on the reverse
side.
500-mg Tablet
NDC 43598-224-14: Bottles of 20
NDC 43598-224-01: Bottles of 100
NDC 43598-224-05: Bottles of 500
875-mg Tablet
NDC 43598-219-14: Bottles of 20
NDC 43598-219-01: Bottles of 100
Powder for Oral Suspension:
Each 5 mL of reconstituted strawberry-flavored suspension
contains 125 mg amoxicillin as the trihydrate. Each 5 mL of reconstituted
bubble-gum-flavored suspension contains 200 mg, 250 mg or 400 mg
amoxicillin as the trihydrate.
125 mg/5 mL
NDC 43598-222-80: 80-mL bottle
NDC 43598-222-52: 100-mL bottle
NDC 43598-222-53: 150-mL bottle
200 mg/5 mL
NDC 43598-223-50: 50-mL bottle
NDC 43598-223-51: 75-mL bottle
NDC 43598-223-52: 100-mL bottle
250 mg/5 mL
NDC 43598-209-80: 80-mL bottle
NDC 43598-209-52: 100-mL bottle
NDC 43598-209-53: 150-mL bottle
400 mg/5 mL
NDC 43598-207-50: 50-mL bottle
NDC 43598-207-51: 75-mL bottle
NDC 43598-207-52: 100-mL bottle
Store at or below 25°C (77°F)- 250 mg and 500 mg Capsules
- 500 mg and 875 mg Tablets
- 200 mg and 400 mg unreconstituted powder
Store Dry Powder at 20°C – 25°C (68°F – 77°F)- 125 mg and 250 mg unreconstituted powder