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Cipro for Treatment of Anthrax Exposure

Brand Name Drug: Cipro

Active Ingredient Drug: ciprofloxacin

Indication: Treatment of bacterial infections; recommended for approval for treatment of anthrax

Company Name: Bayer Corporation

Availability: Already approved and marketed for 17 indications


Anthrax has caused disease in animals for centuries, but its threat as a biological weapon has become most apparent in the last 80 years. Today at least 17 nations are believed to have offensive biological weapons programs in place, and it is not known for sure how many are working with anthrax. Iraq, in particular, has acknowledged that it is producing anthrax for such potential use.

Infection with anthrax, which is caused by the bacterium Bacillus anthracis, is usually fatal. Although penicillin and doxycycline are both approved to treat anthrax, strains of the bacteria have reportedly been engineered to resist these antibiotics.

On July 31, 2000, the FDA Anti-Infective Drug Products Advisory Committee unanimously recommended that the antibiotic Cipro (ciprofloxacin) be approved for use in treating people exposed to aerosolized anthrax bacteria – exposure that would most likely occur during a bioterrorist attack. The drug – a fluoroquinolone – is manufactured by Bayer Corporation and is currently approved for 17 different indications, including respiratory and urinary tract infections.

Cipro (ciprofloxacin): Preclinical Study Results

Data on the efficacy of antibiotics for treating anthrax come from preclinical studies, particularly those in animals. For example, Friedlander et al determined whether a prolonged course of postexposure antibiotics with or without vaccination would protect monkeys exposed to a lethal aerosol dose of Bacillus anthracis when the antibiotic was discontinued. Beginning 1 day after exposure, groups of 10 animals were given penicillin, Cipro (ciprofloxacin), doxycycline, doxycycline plus vaccination, vaccination alone, or saline. Antibiotics were administered for 30 days and then discontinued. Vaccine was given on days 1 and 15.

Two animals died of causes other than anthrax and were not included in the statistical analysis. Nine of 10 controls and 8 of 10 animals given only vaccine died. Each antibiotic regimen completely protected animals while on therapy and provided significant long-term protection upon discontinuance of the drug (penicillin, 7 of 10 survived; ciprofloxacin, 8 of 9 survived; doxycycline, 9 of 10 survived; doxycycline plus vaccination, 9 of 9 survived).

In a study by Kelly et al, concentrations of penicillin, doxycycline, and Cipro were measured by bioassay in sera of rhesus monkeys treated with these drugs for inhalation anthrax. Serum peak and trough concentrations of penicillin, doxycycline, and Cipro (ciprofloxacin), respectively, averaged 2.7 and 0.8, 1.31 and 0.26, and 1.22 and 0.14 microgram/mL. These were within the range usually observed with standard oral doses in humans, and peak concentrations in all monkeys exceeded the MICs for 90% of Bacillus anthracis strains.

Adverse Events

The most common adverse events associated with Cipro are nausea, diarrhea, vomiting, abdominal pain or discomfort, headache, rash, and restlessness. Antacids containing magnesium, aluminum, or calcium, or other products containing metal cations, should be taken 2 hours after or 6 hours before oral administration of Cipro (ciprofloxacin).

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