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Ciprofloxacin Is Not Sole Answer for Anthrax

Kate Traynor

Pharmacists and other health professionals have been quick to question the media's spotlight on ciprofloxacin as the drug of choice to prevent or treat anthrax.

Cipro, Bayer AG’s ciprofloxacin product, became the focus of national attention in early October, when anthrax spores were found in a Florida building that housed a publishing company. People in the area who had been exposed to Bacillus anthracis, the microbe that causes anthrax, began taking Cipro as a prophylactic measure. By mid-October, the prophylaxis regimen had reportedly been extended to thousands of people in New York City, New Jersey, and Washington, D.C., who had also been exposed to B. anthracis.

"It sounds like, listening to the media, that they've just been pushing the Cipro," said Suellyn J. Sorensen, Pharm.D., as the exposure events began to unfold. Sorensen, a clinical pharmacist specialist in infectious diseases at Indiana University Hospital of Clarian Health, added: "I've heard nothing about penicillin and doxycycline."

Before the recent anthrax outbreaks began, the Food and Drug Administration (FDA) recognized penicillin, doxycycline, and ciprofloxacin as treatments for anthrax. Only the product labeling for ciprofloxacin, however, included information on the treatment of inhalational anthrax, the most deadly form of the disease.

FDA announced Oct. 18 that the agency had just approved the use of doxycycline "for the treatment of anthrax in all its forms." In its statement, FDA also said that the agency "is developing more information about the use of this and other antibiotics to treat anthrax and will provide this information soon."

"There is good evidence, against a fully susceptible strain of anthrax, that penicillin, doxycycline, and ciprofloxacin are all effective," said Richard Frothingham, M.D., an infectious diseases and antimicrobial-use specialist at the Veterans Affairs Medical Center in Durham, N.C.

But FDA has reported that some anthrax strains are naturally resistant to penicillins. In addition, the former Soviet Union is suspected to have produced genetically modified B. anthracis that is resistant to tetracyclines. This makes ciprofloxacin the best drug to use for postexposure prophylaxis until the drug susceptibility of the B. anthracis strain in question is determined.

"My understanding is that there is no solid information that strains have been engineered with ciprofloxacin resistance," Frothingham said, noting that "once the susceptibility is known, then all three [drugs] would be reasonable options."

Although FDA has not weighed in on anthrax treatments other than penicillin, doxycycline, and ciprofloxacin, Sorensen speculated that "there’s probably no reason to believe that any of the other quinolones wouldn’t work just as well as Cipro." She named gatifloxacin and levofloxacin as drugs that might be effective against anthrax.

Frothingham also mentioned these drugs as possible treatments for anthrax, but he cautioned about "clear evidence that levofloxacin produces more torsades de pointes and [cardiac] arrhythmia" than does ciprofloxacin. He said he believed that there is not enough evidence in U.S. patients to know whether gatifloxacin also causes cardiac problems.

The Oct. 19 issue of MMWR (PDF) provides interim recommendations for postexposure prophylaxis with ciprofloxacin or doxycycline to prevent inhalational anthrax in children and adults.