Management of Postirradiation Sepsis

Ionizing radiation depresses the immune defenses and enhances susceptibility to local and systemic infection due to endogenous or exogenous microorganisms. Exposure to a lethal dose of ionizing cobalt-60 gamma radiation induces a dose-related reduction in the number of both aerobic and anaerobic bacteria from 10(10-12) to 10(4-6) per gram of stool within 4 days. Whereas the number of anaerobic bacteria stays low, the number of Enterobacteriaceae per gram of stool increases significantly--up to 10(9) by the 12th day following irradiation. This increase is associated with bacterial translocation of these organisms and fatal bacteremia. The use of quinolones was effective in controlling systemic endogenous Gram-negative infection following irradiation. Supplementation with penicillin prevented treatment failures due to Streptococci and increased survival. Quinolones given for 21 days were also effective in the management of systemic exogenous infections due to orally ingested Klebsiella pneumoniae and Pseudomonas aeruginosa. Quinolones may be effective because they inhibit growth of the exogenous organism within the gut lumen while preserving the anaerobic gut flora and their systemic antibacterial activity. Coadministration of antimicrobials effective against anaerobes may be required for the management of polymicrobial infections. The availability of both oral and parenteral routes of administration, the advantage of achieving selective inhibition of potential pathogens in the gut, and the ability to treat systemic infection make the quinolones promising agents for the therapy of endogenous and exogenous infections after irradiation.