The majority of infections occurring in neutropenic patients are caused by gram-negative bacilli. Most infectious disease specialists recommend the combination of a β-lactam antibiotic plus an aminoglycoside antibiotic as initial therapy for presumed infection in these patients. Several investigators have reported data suggesting that the use of two antibiotics that interact synergistically increases the likelihood of a favorable outcome.1,2 This potential for synergistic interaction has supported the selection of a β-lactam-aminoglycoside combination as the most appropriate regimen for these patients. However, the availability of new broad-spectrum penicillins and cephalosporins, sulfamethoxazole and trimethoprim, thienamycins, monolactams, and quinolones requires a reassessment of this concept.
Numerous in vitro studies have shown that β-lactams and aminoglycosides interact synergistically against gram-negative bacilli.3,4 Precise definitions of synergism do not exist and different methodologies ("checkerboard" vs killing curve methods) may produce different results.5 As a general rule, two antibiotics are unlikely to interact synergistically
Bodey GP. Synergy: Should It Determine Antibiotic Selection in Neutropenic Patients? Arch Intern Med. 1985;145(11):1964–1966. doi:10.1001/archinte.1985.00360110034008
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