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Drug Information for CLARITHROMYCIN (KAISER FOUNDATION HOSPITALS): MICROBIOLOGY
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Clarithromycin exerts its antibacterial action by binding to the 50S ribosomal subunit of susceptible microorganisms resulting in inhibition of protein synthesis.
Clarithromycin is active in vitro against a variety of aerobic and anaerobic gram-positive and gram-negative microorganisms as well as most Mycobacterium avium complex (MAC) microorganisms.
Additionally, the 14-OH clarithromycin metabolite also has clinically significant antimicrobial activity. The 14-OH clarithromycin is twice as active against Haemophilus influenzae microorganisms as the parent compound. However, for Mycobacterium avium complex (MAC) isolates the 14-OH metabolite is 4 to 7 times less active than clarithromycin. The clinical significance of this activity against Mycobacterium avium complex is unknown.
Clarithromycin 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
Staphylococcus aureus Streptococcus pneumoniae Streptococcus pyogenesAerobic Gram-negative Microorganisms
Haemophilus influenzae Haemophilus parainfluenzae Moraxella catarrhalisOther Microorganisms
Mycoplasma pneumoniae Chlamydia pneumoniae (TWAR)Mycobacteria
Mycobacterium avium complex (MAC) consisting of: Mycobacterium avium Mycobacterium intracellulare
Beta-lactamase production should have no effect on clarithromycin activity.
NOTE: Most strains of methicillin-resistant and oxacillin-resistant staphylococci are resistant to clarithromycin.
Omeprazole/clarithromycin dual therapy; ranitidine bismuth citrate/clarithromycin dual therapy; omeprazole/clarithromycin/amoxicillin triple therapy; and lansoprazole/clarithromycin/amoxicillin triple therapy have been shown to be active against most strains of Helicobacter pylori in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.Helicobacter
Helicobacter pyloriPretreatment Resistance
Clarithromycin pretreatment resistance rates were 3.5% (4/113) in the omeprazole/clarithromycin dual therapy studies (M93-067, M93-100) and 9.3% (41/439) in the omeprazole/clarithromycin/amoxicillin triple therapy studies (126, 127, M96-446). Clarithromycin pretreatment resistance was 12.6% (44/348) in the ranitidine bismuth citrate/clarithromycin b.i.d. versus t.i.d. clinical study (H2BA3001). Clarithromycin pretreatment resistance rates were 9.5% (91/960) by E-test and 11.3% (12/106) by agar dilution in the lansoprazole/clarithromycin/amoxicillin triple therapy clinical trials (M93-125, M93-130, M93-131, M95-392, and M95-399).
Amoxicillin pretreatment susceptible isolates (less than 0.25 µg/mL) were found in 99.3% (436/439) of the patients in the omeprazole/clarithromycin/amoxicillin clinical studies (126, 127, M96-446). Amoxicillin pretreatment minimum inhibitory concentrations (MICs) greater than 0.25 µg/mL occurred in 0.7% (3/439) of the patients, all of whom were in the clarithromycin/amoxicillin study arm. Amoxicillin pretreatment susceptible isolates ( less than 0.25µg/mL) occurred in 97.8% (936/957) and 98.0% (98/100) of the patients in the lansoprazole/clarithromycin/amoxicillin triple-therapy clinical trials by E-test and agar dilution, respectively. Twenty-one of the 957 patients (2.2%) by E-test and 2 of 100 patients (2.0%) by agar dilution had amoxicillin pretreatment MICs of greater than 0.25 µg/mL. Two patients had an unconfirmed pretreatment amoxicillin minimum inhibitory concentration (MIC) of greater than 256 µg/mL by E-test.
a Includes only patients with pretreatment clarithromycin susceptibility tests
b Susceptible (S) MIC less than 0.25 µg/mL, Intermediate (I) MIC 0.5-1.0 µg/mL, Resistant (R) MIC greater than 2 µg/mL
Patients not eradicated of H. pylori following omeprazole/clarithromycin, ranitidine bismuth citrate/clarithromycin, omeprazole/clarithromycin/amoxicillin, or lansoprazole/clarithromycin/ amoxicillin therapy would likely have clarithromycin resistant H. pylori isolates. Therefore, for patients who fail therapy, clarithromycin susceptibility testing should be done, if possible. Patients with clarithromycin resistant H. pylori should not be treated with any of the following: omeprazole/clarithromycin dual therapy; ranitidine bismuth citrate/clarithromycin dual therapy; omeprazole/clarithromycin/amoxicillin triple therapy; lansoprazole/clarithromycin/amoxicillin triple therapy; or other regimens which include clarithromycin as the sole antimicrobial agent.Amoxicillin Susceptibility Test Results and Clinical/Bacteriological Outcomes
In the omeprazole/clarithromycin/amoxicillin triple-therapy clinical trials, 84.9% (157/185) of the patients who had pretreatment amoxicillin susceptible MICs (less than 0.25 µg/mL) were eradicated of H. pylori and 15.1% (28/185) failed therapy. Of the 28 patients who failed triple therapy, 11 had no post-treatment susceptibility test results, and 17 had post-treatment H. pylori isolates with amoxicillin susceptible MICs. Eleven of the patients who failed triple therapy also had post-treatment H. pylori isolates with clarithromycin resistant MICs.
In the lansoprazole/clarithromycin/amoxicillin triple-therapy clinical trials, 82.6% (195/236) of the patients that had pretreatment amoxicillin susceptible MICs (less than 0.25 µg/mL) were eradicated of H. pylori. Of those with pretreatment amoxicillin MICs of greater than 0.25 µg/mL, three of six had the H. pylori eradicated. A total of 12.8% (22/172) of the patients failed the 10- and 14-day triple-therapy regimens. Post-treatment susceptibility results were not obtained on 11 of the patients who failed therapy. Nine of the 11 patients with amoxicillin post-treatment MICs that failed the triple-therapy regimen also had clarithromycin resistant H. pylori isolates.
The following in vitro data are available, but their clinical significance is unknown. Clarithromycin exhibits in vitro activity against most strains of the following microorganisms; however, the safety and effectiveness of clarithromycin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.Aerobic Gram-positive Microorganisms
Streptococcus agalactiae Streptococci (Groups C, F, G)Viridans group streptococciAerobic Gram-negative Microorganisms
Bordetella pertussis Legionella pneumophila Pasteurella multocidaAnaerobic Gram-positive Microorganisms
Clostridium perfringens Peptococcus niger Propionibacterium acnesAnaerobic Gram-negative Microorganisms
Prevotella melaninogenica (formerly Bacteriodes melaninogenicus)Susceptibility Testing Excluding Mycobacteria and Helicobacter
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