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Assessment of the relative risk of antibiotic resistance associated with the use of different classes of antibiotics; and with particular antibiotics within classes

A recent history of antibiotic use increases the risk of resistance in the infecting isolate, particularly within the class of antibiotics (Figure 3). Prior receipt of any antibiotic increases the chance that an infecting isolate will be resistant to penicillins or cephalosporins. Prior use of macrolides, trimethroprim-sulfamethoxazole or levofloxacin is associated primarily with a class-specific effect: that is, a patient who has previously been given a macrolide antibiotic is much more likely to have a macrolide resistant isolate, than a patient who has received any other class of antibiotic.

Figure 3: Antibiotic resistance in S. pneumoniae by history of prior antibiotic use

figure 3

In Figures 4 and 5, the effects of different fluoroquinolones are compared. Figure 4 shows the effect of the use of any flouroquinolone on resistance to the different respiratory fluoroquinolones.

Figure 4: Rate of fluoroquinolone resistance in isolates from patients who have and have not had prior therapy with any fluoroquinolone

figure 4

More than 95% of isolates from patients with a history of recent fluoroquinolone use remain susceptible.

Figure 5: Rate of fluoroquinolone resistance in isolates from patients who have and have not had prior therapy with the same fluoroquinolone

figure 5

In Figure 5, resistance to individual fluoroquinolones is shown based on which fluoroquinolone was used in the past. Thus, 0.77% of isolates are resistant to levofloxacin if the patient had not had fluoroquinolones in the past three months. In patients who had been given a fluoroquinolone other than levofloxacin, 8.3% of isolates were resistant. In patients who had received levofloxacin, 13% of isolates were resistant. The comparative figures for moxifloxacin are 0.13% for patient who had not received a fluoroquinolone, 0.55% for patients who had received a quinolone other than moxifloxacin, and 0 for patients who had received moxifloxacin. (Note that some caution must be excercised here; numbers are currently limited for moxifloxacin because of its recent licensure, and the difference between 0.55% and 0 has not yet achieved statistical significance).

[Click here to access PowerPoint file containing the above graphs.]


 

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