A short course of antibiotic treatment is effective in preventing death from experimental inhalational anthrax after discontinuing antibiotics.
BACKGROUND
Postexposure prophylaxis of inhalational anthrax requires prolonged antibiotic therapy or antibiotics and vaccination. The duration of treatment for established anthrax is controversial, because retained spores may germinate and cause disease after antibiotics are discontinued. Using rhesus macaques, we determined whether a short course of antibiotic treatment, as opposed to prophylaxis, could effectively treat inhalational anthrax and prevent disease caused by the germination of spores after discontinuation of antibiotics.


METHODS
Two groups of 10 rhesus macaques were exposed to an aerosol dose of Bacillus anthracis spores. Animals in group 1 received ciprofloxacin prophylaxis beginning 1-2 h after exposure. Those in group 2 began receiving ciprofloxacin after becoming bacteremic, and treatment was continued for 10 days. When each group 2 animal completed 10 days of therapy, the prophylactic antibiotic was discontinued in the paired group 1 animal.


RESULTS
In group 1 (prophylaxis), no deaths occurred during antibiotic treatment, but only 2 (20%) of 10 animals survived after antibiotics were discontinued. In contrast, in group 2 (treatment), 3 deaths occurred during antibiotic treatment, but all 7 animals (100%) alive after 10 days of therapy survived when antibiotics were discontinued.


CONCLUSIONS
In the treatment of inhalational anthrax, the prolonged course of antibiotics required to achieve prophylaxis may not be necessary to prevent anthrax that results from the germination of retained spores after the discontinuation of antibiotics.
Vietri
Nicholas J
NJ
Division of Bacteriology, Center for Aerobiological Sciences, US Army Medical Research Institute of Infectious Diseases, Frederick, Maryland 21702, USA. nicholas.vietri@amedd.army.mil
Purcell
Bret K
BK
Tobery
Steven A
SA
Rasmussen
Suzanne L
SL
Leffel
Elizabeth K
EK
Twenhafel
Nancy A
NA
Ivins
Bruce E
BE
Kellogg
Mark D
MD
Webster
Wendy M
WM
Wright
Mary E
ME
Friedlander
Arthur M
AM
D000280:Administration, Inhalation; D000336:Aerosols; D000818:Animals; D000881:Anthrax / Q000188:drug therapy* / Q000401:mortality*; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D023482:Bioterrorism; D002939:Ciprofloxacin / Q000008:administration & dosage* / Q000627:therapeutic use; D004195:Disease Models, Animal; D005260:Female; D008253:Macaca mulatta; D008297:Male; D011897:Random Allocation
D000336:Aerosols; D000900:Anti-Bacterial Agents; D002939:Ciprofloxacin