The purpose of this clinical trial is to determine whether there is any effect on the antibiotic, ciprofloxacin when taken before and after administration of a 3-dose series of BioThrax® (Anthrax Vaccine Adsorbed or AVA).

This study will be conducted in the United States (US) in 154 healthy male and female volunteer subjects ages 18 to 45.

The duration of study participation for each subject will be approximately 76 days (approximately 2.5 months)

BioThrax is the only FDA-licensed vaccine for the prevention of anthrax infection. This is a randomized, open-label, Phase 2, multi-center trial to investigate the potential interactions of ciprofloxacin and BioThrax.

Inclusion Criteria:

• Be between 18 and 45 years of age, at the time of enrollment
• Be in good health as determined by the investigator from medical history and a physical examination.
• If a pre-menopausal female, must be using acceptable methods of birth control.
• Be willing and able to return for all follow-up visits and blood and urine collections for the duration of the trial
• Be willing and able to complete a web-enabled electronic diary and report concomitant medications, adverse events, and BioThrax reactogenicity events during the trial
• Be able to understand and communicate in English.

Exclusion Criteria:

• Prior immunization with anthrax vaccine or known exposure to anthrax organisms
• Intend to enlist in the military during the study.
• Have a known allergy to aluminum hydroxide, formaldehyde, benzethonium chloride, or latex.
• Plan to receive experimental products 30 days prior to study entry or at any time during the study
• Have received a live vaccine in the 30 days before study entry
• Plan to receive a live vaccine at any time during the study.
• Have ongoing drug abuse/dependence (including alcohol) issues and/or test positive in a urine drug screen for amphetamines, barbiturates, cocaine or opiates
• Have received immunosuppressive therapy (including systemic steroids) within 30 days prior to trial entry
• Have any other condition known to produce or be associated with immunosuppression
• Have received cytotoxic therapy in the previous 5 years
• A chronic condition that, in the opinion of the Investigator, would render vaccination unsafe or would interfere with trial evaluations or completion of the study.

Intent to treat population: all subjects who were randomized.

Arm 1: enrollment, Days 0-5, 20, 34, 39-44, 48, or the early withdrawal visit (EWV) for a max of 16 visits. Arm 2: enrollment, Days 1, 5, 20, 34, 48, or EWV for a max of 6 visits. Arm 3: enrollment, Days 1, 15, 29, 43, or EWV for a max of 5 visits.

Subjects in the safety (treated) population were asked about adverse event (AEs) at each visit. Severe (Grade 3) injection site and systemic reactions recorded in subject diaries were also recorded as AEs in the eCRF. Abnormal lab results, vital signs, and physical examination findings considered clinically significant were also recorded as AEs.