Other
Rx Only
Rev. 12/06
To reduce the development of drug-resistant bacteria and maintain the effectiveness of amoxicillin and other antibacterial drugs, amoxicillin should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.
Microbiology: amoxicillin is similar to ampicillin in its bactericidal action against susceptible organisms during the stage of active multiplication. It acts through the inhibition of biosynthesis of cell wall mucopeptide. Amoxicillin 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 section.
Aerobic Gram-Positive Microorganisms:
Enterococcus faecalis
Staphylococcus spp.* (β-lactamase–negative strains only)
Streptococcus pneumoniae
Streptococcus spp. (α- and β-hemolytic strains only)
* Staphylococci which are susceptible to amoxicillin but resistant to methicillin/oxacillin should be considered as resistant to amoxicillin.
Aerobic Gram-Negative Microorganisms:
Escherichia coli (β-lactamase–negative strains only)
Haemophilus influenzae (β-lactamase–negative strains only)
Neisseria gonorrhoeae (β-lactamase–negative strains only)
Proteus mirabilis (β-lactamase–negative strains only)
Helicobacter:
Helicobacter pylori
Susceptibility Tests:Dilution Techniques: Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimi-crobial 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 ampicillin powder. Ampicillin is sometimes used to predict susceptibility of S. pneumoniae to amoxicillin; however, some intermediate strains have been shown to be susceptible to amoxicillin. Therefore, S. pneumoniae susceptibility should be tested using amoxicillin powder.
The MIC values should be interpreted according to the following criteria:
For Gram-Positive Aerobes:
| MIC (mca /mL) | Interpretation |
| ≤ 8 | Susceptible (S) |
| ≥ 16 | Resistant (R) |
| MIC (mca /mL) | Interpretation |
| ≤ 0.25 | Susceptible (S) |
| ≥ 0.5 | Resistant (R) |
| MIC (mca /mL) | Interpretation |
| ≤ 0.25 | Susceptible (S) |
| 0.5 to 4 | Intermediate (I) |
| ≥ 8 | Resistant (R) |
| MIC (mca /mL) | Interpretation |
| ≤ 2 | Susceptible (S) |
| 4 | Intermediate (I) |
| ≥ 8 | Resistant (R) |
NOTE: These interpretive criteria are based on the recommended doses for respiratory tract infections.
For Gram-Negative Aerobes:
| MIC (mca /mL) | Interpretation |
| ≤ 8 | Susceptible (S) |
| 16 | Intermediate (I) |
| ≥ 32 | Resistant (R) |
a. Staphylococci which are susceptible to amoxicillin but resistant to methicillin/oxacillin should be considered as resistant to amoxicillin. | |
b. These interpretive standards are applicable only to broth microdilution susceptibility tests using cation-adjusted Mueller-Hinton broth with 2-5% lysed horse blood. | |
c. These interpretive standards are applicable only to broth microdilution test with H. influenzae using Haemophilus Test Medium (HTM).1 | |
| MIC (mcg/mL) | Interpretation |
| ≤ 1 | Susceptible (S) |
| 2 | Intermediate (I) |
| ≥ 4 | 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 ampicillin powder should provide the following MIC values:
| Microorganism | MIC (mcg /mL) | |
| E. coli | ATCC 25922 | 2 to 8 |
| E. faecalis | ATCC 29212 | 0.5 to 2 |
| H. influenzae | ATCC 49247d | 2 to 8 |
| S. aureus | ATCC 29213 | 0.25 to 1 |
Using amoxicillin to determine susceptibility:
d. This quality control range is applicable to only H. influenzae ATCC 49247 tested by a broth microdilution procedure using HTM. 1 | ||
e. This quality control range is applicable to only S. pneumoniae ATCC 49619 tested by the broth microdilution procedure using cation-adjusted Mueller-Hinton broth with 2-5% lysed horse blood. | ||
| Microorganism | MIC Range (mcg /mL) | |
| S. pneumoniae | ATCC 49619e | 0.03 to 0.12 |
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 standardized inoculum concentrations. This procedure uses paper disks impregnated with 10 mcg ampicillin to test the susceptibility of microorganisms, except S. pneumoniae, to amoxicillin. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for ampicillin.
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 following criteria:
For gram-positive aerobes:
| Zone Diameter (mm) | Interpretation |
| ≥ 17 | Susceptible (S) |
| ≤ 16 | Resistant (R) |
| Zone Diameter (mm) | Interpretation |
| ≥ 29 | Susceptible (S) |
| ≤ 28 | Resistant (R) |
| Zone Diameter (mm) | Interpretation |
| ≥ 26 | Susceptible (S) |
| 19 to 25 | Intermediate (I) |
| ≤ 18 | Resistant (R) |
NOTE: For streptococci (other than β-hemolytic streptococci and S. pneumoniae), an ampicillin MIC should be determined.
S. pneumoniae
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.
For gram-negative aerobes:
| Zone Diameter (mm) | Interpretation |
| ≥17 | Susceptible (S) |
| 14 to 16 | Intermediate (I) |
| ≤13 | Resistant (R) |
f. Staphylococci which are susceptible to amoxicillin but resistant to methicillin/oxacillin should be considered as resistant to amoxicillin. | |
g. These interpretive standards are applicable only to disk diffusion susceptibility tests with H. influenzae using Haemophilus Test Medium (HTM).2 | |
| Zone Diameter (mm) | Interpretation |
| ≥ 22 | Susceptible (S) |
| 19 to 21 | Intermediate fl) |
| ≤18 | Resistant (R) |
Interpretation should be as stated above for results using dilution techniques.
As with standard dilution techniques, disk diffusion susceptibility test procedures require the use of laboratory control microorganisms. The 10 mcg ampicillin disk should provide the following zone diameters in these laboratory test quality control strains:
| Microorqanism | Zone Diameter | |
| (mm) | ||
| E. coli | ATCC 25922 | 16 to 22 |
| H. influenzae | ATCC 49247h | 13 to 21 |
| S. aureus | ATCC 25923 | 27 to 35 |
Using 1 mcg oxacillin disk:
h. This quality control range is applicable to only H. influenzae ATCC 49247 tested by a disk diffusion procedure using HTM.2 | ||
i. This quality control range is applicable to only S. pneumoniae ATCC 49619 tested by a disk diffusion procedure using Mueller-Hinton agar supplemented with 5% sheep blood and incubated in 5% CO2. | ||
| Microorganism | Zone Diameter | |
| (mm) | ||
| S. pneumoniae | ATCC 49619i | 8 to 12 |
Susceptibility testing forHelicobacter pylori:In vitro susceptibility testing methods and diagnostic products currently available for determining minimum inhibitory concentrations (MICs) and zone sizes have not been standardized, validated, or approved for testing H. pylori microorganisms.
Culture and susceptibility testing should be obtained in patients who fail triple therapy. If clarithromycin resistance is found, a non-clarithromycin-containing regimen should be used.
Triple therapy:amoxicillin/clarithromycin/lansoprazole:
The most frequently reported adverse events for patients who received triple therapy were diarrhea (7%), headache (6%), and taste perversion (5%). No treatment-emergent adverse events were observed at significantly higher rates with triple therapy than with any dual therapy regimen.
Dual therapy:Amoxicillin/lansoprazole:
The most frequently reported adverse events for patients who received amoxicillin 3 times daily plus lansoprazole three times daily dual therapy were diarrhea (8%) and headache (7%). No treatment-emergent adverse events were observed at significantly higher rates with amoxicillin 3 times daily plus lansoprazole 3 times daily dual therapy than with lansoprazole alone.
For more information on adverse reactions with clarithromycin or lansoprazole, refer to their package inserts, ADVERSE REACTIONS.
General: It should be recognized that in the treatment of chronic urinary tract infections, frequent bacteriological and clinical appraisals are necessary. Smaller doses than those recommended above should not be used. Even higher doses may be needed at times. In stubborn infections, therapy may be required for several weeks. It may be necessary to continue clinical and/or bacteriological follow-up for several months after cessation of therapy. Except for gonorrhea, treatment should be continued for a minimum of 48 to 72 hours beyond the time that the patient becomes asymptomatic or evidence of bacterial eradication has been obtained. It is recommended that there be at least 10 days' treatment for any infection caused by Streptococcus pyogenes to prevent the occurrence of acute rheumatic fever.
H. pylori eradication to reduce the risk of duodenal ulcer recurrence:
Triple therapy: Amoxicillin/clarithromycin/lansoprazole
The recommended adult oral dose is 1 gram amoxicillin, 500 mg clarithromycin, and 30 mg lansoprazole, all given twice daily (q12h) for 14 days. (See INDICATIONS AND USAGE.)
Dual therapy: Amoxicillin/lansoprazole
The recommended adult oral dose is 1 gram amoxicillin and 30 mg lansoprazole, each given three times daily (q8h) for 14 days. (See INDICATIONS AND USAGE.)
Please refer to clarithromycin and lansoprazole full prescribing information for CONTRAINDICATIONS and WARNINGS, and for information regarding dosing in elderly and renally impaired patients.
Dosing recommendations for adults with impaired renal function: Patients with impaired renal function do not generally require a reduction in dose unless the impairment is severe. Severely impaired patients with a glomerular filtration rate of <30 mL/min. should not receive the 875-mg tablet. Patients with a glomerular filtration rate of 10 to 30 mL/min. should receive 500 mg or 250 mg every 12 hours, depending on the severity of the infection. Patients with a less than 10 mL/minute glomerular filtration rate should receive 500 mg or 250 mg every 24 hours, depending on severity of the infection.
Hemodialysis patients should receive 500 mg or 250 mg every 24 hours, depending on severity of the infection. They should receive an additional dose both during and at the end of dialysis.
There are currently no dosing recommendations for pediatric patients with impaired renal function.