September 11, 2001 : Attack on America
Antimicrobial Susceptibility of Bacillus anthracis Isolates Associated with Intentional Distribution in Florida, New Jersey, New York, Pennsylvania, Virginia, and Washington, D.C., September - October, 2001 9:12 PM EDT; October 22, 2001
Distributed via the Health Alert Network
October 22, 2001, 21:12 EDT (9:12 PM EDT)
Antimicrobial Susceptibility of Bacillus anthracis Isolates Associated with Intentional Distribution in Florida, New Jersey, New York, Pennsylvania, Virginia, and Washington, D.C., September - October, 2001
The antimicrobial susceptibility patterns of eleven Bacillus anthracis isolates associated with intentional exposures on the east coast have been determined. The susceptibility patterns of all the isolates were similar and are described below. CDC will be issuing updated treatment recommendations for anthrax and will disseminate them as soon as they are completed.
Ciprofloxacin <0.06 (SUSCEPTIBLE)
Tetracycline = 0.06 µg/ml (susceptible)
Doxycycline <0.03 (SUSCEPTIBLE)
Penicillin <0.06 BELOW)
Amoxicillin
Erythromycin = 1 µg/ml (intermediate)
Azithromycin =2 µg/ml (borderline susceptible)
Clarithromycin =0.25 µg/ml (susceptible)
Rifampin = 0.5 µg/ml (susceptible)
Clindamycin <0.5 (SUSCEPTIBLE)
Vancomycin = 1-2 µg/ml (susceptible)
Chloramphenicol = 4 µg/ml (susceptible)
Ceftriaxone = 16 -32 µg/ml (intermediate or resistant)
- The penicillin MICs were <0.06 WHICH, IS FOR CONSIDERED DEFINED USING BE (RESISTANCE 0.12 THE AS BREAKPOINT TO WOULD µG/ML, SUSCEPTIBLE NCCLS PENICILLIN, STAPHYLOCOCCAL>0.25 µg/ml).
- All of the B. anthracis isolates were also susceptible to ciprofloxacin (MIC
- Although there are no amoxicillin breakpoints defined for staphylococci by NCCLS, the amoxicillin results (MIC <0.03 ERYTHROMYCIN ISOLATES. STUDIES ADDITIONAL
Conclusions
- The current B. anthracis strains associated with the intentional exposures are susceptible to ciprofloxacin and doxycycline, the two drugs approved for post-exposure prophylaxis to B. anthracis and recommended as part of initial therapy of inhalational or cutaneous anthrax.
- The current strains also are susceptible to chloramphenicol, clindamycin, rifampin, vancomycin, and clarithromycin, but limited or no data exists regarding the use of these agents in the treatment or prophylaxis of B. anthracis infections.
- Cephalosporins should not be used for post-exposure prophylaxis or treatment of B. anthracis infections.
- The likelihood of a beta-lactamase induction event that would increase penicillin MICs is significantly higher in infections where high concentrations of organisms are present. Thus, treatment of known B. anthracis infections with a penicillin type drug alone (i.e., penicillin G, ampicillin, etc.) in the setting where high concentrations of organisms are present is a concern.
- The likelihood of a beta-lactamase induction event that would increase penicillin MICs is lower when only small numbers of vegetative cells are present, such as during post exposure prophylaxis. Thus, amoxicillin or penicillin VK may be an option for post-exposure prophylaxis where ciprofloxacin or doxycycline are contraindicated.
- Additional studies are in progress to assess the susceptibility of the penicillinase activity observed in these strains to beta-lactamase inhibitors.
- Clinical experience is limited, but combination therapy with two or more antimicrobials may be appropriate in patients with severe infection.
Source:
U.S. Government Website
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