Four antibiotics are FDA-approved for use for PEP following exposure to aerosolized spores of B. anthracis: doxycycline, ciprofloxacin, levofloxacin, and parenteral procaine penicillin G.1 Levofloxacin was approved for PEP for anthrax in 2004 for adults and in 2008 for children (FDA, 2004, 2008a). Controlled human efficacy studies involving anthrax are not possible, so FDA approval of the inhalational anthrax PEP indications was based on animal efficacy studies and the large safety database for these antibiotics in humans (FDA, 2000b, 2002, 2008b, 2009).2
For adults ages 18 to 65 who have potentially been exposed to aerosolized spores of B. anthracis, the Centers for Disease Control and Prevention (CDC) recommends 60 days of treatment with either ciprofloxacin or doxycycline plus a three-dose series of anthrax vaccine adsorbed (AVA) starting as soon as possible after exposure (CDC, 2010; Stern et al., 2008).3 CDC recommends that levofloxacin be reserved as a second-line agent, as safety data on its use in treatment for longer than 28 days are limited (Stern et al., 2008). Levofloxacin should be used only when treatment with first-line therapies is hampered by patient drug tolerance issues or antimicrobial resistance patterns (Stern et al., 2008). For children, ciprofloxacin or doxycycline also is used for first-line antimicrobial PEP. Because of the potential for serious adverse events, however, CDC recommends off-label use of amoxicillin as the preferred PEP agent if the anthrax strain is proven to be susceptible to that drug (CDC, 2005, 2010). Additional challenges of administering anthrax PEP to children include limited data on appropriate dosing and palatability of drug formulations. There is currently no recommendation for use of AVA in children; however, its use for those under age 18 is currently being considered (CDC, 2010).4
1Note that no oral penicillin-class of antibiotic is currently FDA-approved for postexposure prophylaxis (PEP) for anthrax. Current drug information, including PEP dosing for adults and children, is available on the FDA website at http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm063485.htm. For certain patient groups, including children and pregnant women, the Centers for Disease Control and Prevention (CDC) recommends off-label use of amoxicillin if susceptibility testing proves that the anthrax strain is susceptible (CDC, 2005).
2See Meyerhoff and Murphy (2002) for a detailed presentation of the antibiotics that were approved by the Food and Drug Administration for anthrax postexposure prophylaxis as of 2001.
3See CDC (2010), Table 1, for a summary of the current CDC recommendations for PEP with antimicrobial agents and AVA, available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5906a1.htm.
4On July 7, 2011, the National Biodefense Science Board (NBSB), at the written request of the Department of Health and Human Services’ Assistant Secretary for Preparedness and Response (ASPR), convened an initial meeting to discuss vaccine to protect children from anthrax. The NBSB reported to the ASPR in October 2011. See http://www.phe.gov/Preparedness/Legal/boards/nbsb/recommendations/Documents/avwgrpt1103.pdf.