Selective decontamination of the digestive tract and its role in antimicrobial prophylaxis

Selective decontamination of the digestive tract (SDD) is an established form of infection prevention which relies upon local antibiotic action to afford suppression of potential pathogens while preserving 'colonization resistance' (CR). However, CR has never been shown conclusively to play a decisive role in either achieving or maintaining effective prophylaxis in patients and by employing absorbable antimicrobials or parenteral antibiotics, prophylaxis is actually achieved by both local and systemic action. The role of prophylaxis in neutropenic patients is also far from clear since morbidity and mortality remain the same whether or not prophylactic antibacterials are given and most patients still require empirical therapy for fever. In addition, the Gram-positive cocci, rather than Gram-negative bacilli presently predominate as pathogens. There is also an increasing trend towards including fungal and viral infection as targets for prophylaxis. Moreover, current anti-infective strategies are more akin to 'pre-emptive therapy' (PET) since the antimicrobials are available systemically and given at optimum therapeutic doses and there is little to distinguish treatment given to prevent colonization from progressing to infection from that used to arrest incipient infection or effect a cure of established infection. In contrast, SDD as originally conceived may well prove cost-effective for the prevention of infection in intensive care although neither the optimum regimen nor the patient group who would gain most benefit have been defined. None the less, by affording protection against Gram-negative sepsis, both SDD and PET would reduce the pressure on the clinicians to treat empirically and shift the emphasis once more on appropriate investigations which would involve the microbiologist more directly and immediately in patient care. Any savings from lowering the drug usage could then be diverted to improving diagnosis and providing the regular monitoring that is essential to the success of both PET and SDD.