Antimicrobial prophylaxis in the neutropenic host: lessons of the past and perspectives for the future.

Most attempts at preventing infection in neutropenic hosts have involved isolation of the patient from potential disease-causing microbes and the use of prophylatic antibiotics. Laminar airflow units were an expensive approach and the principal benefit may well have come from simultaneously administered regimens that suppressed the gut flora. The relationship between colonization of the gut by organisms that can subsequently cause systemic disease and gram-negative bacteremia has been supported by many observations, but the role of the normal anaerobic gastrointestinal flora in limiting overgrowth by potentially virulent gram-negative bacilli remains controversial. Cotrimoxazole has been a popular agent for prophylaxis but has serious deficiencies including lack of activity against Pseudomonas aeruginosa. Emergence of bacterial resistance to cotrimoxazole is an increasing problem. At present, the new fluoroquinolones offer promise as active agents against most gram-negative and some gram-positive pathogens but these agents lack anti-pneumocystis activity. It is widely perceived that improvements in clinical study design are needed in order to critically evaluate new developments in the field of antibiotic prophylaxis.