Principle of antimicrobial management of infections after accidental or hostile exposure to iradiation

Radiation sickness (acute radiation syndrome, or ARS) occurs when the body is exposed to a high dose of penetrating radiation within a short period of time. The first symptoms of ARS typically are fatigue, hair loss, nausea, vomiting and diarrhea, as well as skin changes such as swelling, redness, itching and radiation burns. Symptoms may present within a few minutes to days after the exposure, and may come and go. This seriously ill stage may last from a few hours up to several months. Systemic infection is one of the complications of ARS.

 Treatment of ARS includes both general supportive care and specific actions and medications. ( Reeves GI. Medical implications of enhanced radiation weapons. Mil Med. 2010 ;175:964 ) The administration of proper antimicrobial therapy is essential for the prevention and treatment of systemic infection from endogenous and exogenous organisms that can occur following exposure to ionizing radiation. ( Brook et al. Management of postirradiation infection: lessons learned from animal models. Mil Med 2004;169:194) The management of these patients includes also the use of specific and non-specific biological response modifiers or immunomodulators. Care must be taken of any conventional injuries, and affected organ systems.

 ARS is usually caused by radiation exposure, not internal contamination. Ionizing radiation suppresses the host defenses and increases it’s susceptibility to local and systemic infection caused by endogenous or exogenous organisms. 

Exposure of rodents to ionizing ⁶⁰Co-gamma radiation caused changes in the number of bacteria within the gut. There is a dose-related decease in the number of both aerobic and anaerobic bacteria from 10^10-12 to 10^4-6 /gram of stool within four days. The number of anaerobic bacteria stays low, but the quantities of Enterobacteriaceae per gram of stool increases significantly up to 10⁹ by the 12^th day after exposure to irradiation. This increase is associated with bacterial translocation of these microorganisms and lethal bacteremia. The administration of flouroquinolones to irradiated animals was successful in controlling systemic endogenous Gram-negative infection that develops after irradiation. The supplementation of flouroquinolone therapy with penicillin prevented treatment failures due to infection with Streptococcus spp. and increased the survival of the animals. Flouroquinolones administered for 21 days also were effective in the treatment of systemic exogenous infections due to orally ingested aerobic Gram negative bacilli (i.e. Klebsiella pneumoniae and Pseudomonas aeruginosa). The effectiveness of flouroquinolones may be due to their ability to inhibit the growth of exogenous organisms inside the gut lumen, while preserving the anaerobic gastrointestinal flora as well as their systemic antibacterial efficacy. Based on these findings the antimicrobials recommended for the therapy of infection the emerge after exposure to ionizing irradiation are: ciprofloxacin, levofloxacin, ceftriaxone, cefepime, gentamicin +/- amoxicillin or vancomycin.