Ciprofloxacin Extended-release (Page 3 of 12)

Susceptibility Test Methods

When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drug products 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 antibacterial 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 test method (broth and/or agar).1 The MIC values should be interpreted according to criteria provided in Table 1.
  • Diffusion Techniques: Quantitative methods that require measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using a standardized test method.2 This procedure uses paper disks impregnated with 5 mcg ciprofloxacin to test the susceptibility of bacteria to ciprofloxacin. The disc diffusion interpretive criteria are provided in Table 1.
Table 1: Susceptibility Test Interpretive Criteria for Ciprofloxacin
Species MIC (mcg/mL) Zone Diameter (mm)
S=Susceptible, I=Intermediate, and R=Resistant.
Enterobacteriaceae ≤1 2 ≥4 ≥21 16-20 ≤15
Enterococcus faecalis ≤1 2 ≥4 ≥21 16-20 ≤15
Pseudomonas aeruginosa ≤1 2 ≥4 ≥21 16-20 ≤15
Staphylococcus saprophyticus ≤1 2 ≥4 ≥21 16-20 ≤15

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.

  • Quality Control: Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures.1,2 For dilution technique, standard ciprofloxacin powder should provide the MIC values according to criteria outlined in Table 2. For diffusion technique, the 5 mcg ciprofloxacin disk should provide the zone diameters outlined in Table 2.
    Table 2: Quality Control for Susceptibility Testing of Ciprofloxacin
    Strains MIC range(mcg/mL) Zone Diameter(mm)
    Enterococcus faecalis ATCC 292120.25-2-
    Escherichia coli ATCC 259220.004-0.01530-40
    Pseudomonas aeruginosa ATCC 278530.25-1.025-33
    Staphylococcus aureus ATCC 292130.12-0.5-
    Staphylococcus aureus ATCC 25923-22-30


Ciprofloxacin extended-release tablets are indicated only for the treatment of urinary tract infections, including acute uncomplicated pyelonephritis, caused by susceptible strains of the designated microorganisms as listed below. Ciprofloxacin extended-release tablets and ciprofloxacin immediate-release tablets are not interchangeable. Please see DOSAGE AND ADMINISTRATION for specific recommendations.

Uncomplicated Urinary Tract Infections (Acute Cystitis) caused by Escherichia coli, Proteus mirabilis, Enterococcus faecalis, or Staphylococcus saprophyticus a.

Complicated Urinary Tract Infections caused by Escherichia coli, Klebsiella pneumoniae, Enterococcus faecalis, Proteus mirabilis, or Pseudomonas aeruginosa*.

Acute Uncomplicated Pyelonephritis caused by Escherichia coli.

* Treatment of infections due to this organism in the organ system was studied in fewer than 10 patients.

THE SAFETY AND EFFICACY OF CIPROFLOXACIN EXTENDED-RELEASE TABLETS IN TREATING INFECTIONS OTHER THAN URINARY TRACT INFECTIONS HAS NOT BEEN DEMONSTRATED. Appropriate culture and susceptibility tests should be performed before treatment in order to isolate and identify organisms causing infection and to determine their susceptibility to ciprofloxacin. Therapy with ciprofloxacin extended-release tablets may be initiated before results of these tests are known; once results become available appropriate therapy should be continued. Culture and susceptibility testing performed periodically during therapy will provide information not only on the therapeutic effect of the antimicrobial agent but also on the possible emergence of bacterial resistance.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of ciprofloxacin extended-release tablets and other antibacterial drugs, ciprofloxacin extended-release tablets should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

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