INFLUENCE OF CYTOSTATIC TREATMENT ON THE EFFICACY OF ERYTHROMYCIN AND ROXITHROMYCIN IN A STAPHYLOCOCCAL INFECTION IN MICE

Mice made monocytopenic with etoposide or both granulocytopenic and monocytopenic with cyclophosphamide were infected in a thigh muscle with 3×106 CFU of Staphylococcus aureus; 1 h later erythromycin or roxithromycin was administered, and 4 h after that the number of CFU per thigh was determined. In vitro as well as in vivo, the maximal effect of both antibiotics was only bacteriostatic. Monocytopenia did not diminish the efficacy of either erythromycin or roxithromycin in vivo, whereas the combination of granulocytopenia and monocytopenia markedly decreased the efficacy of both drugs: a 4-fold dose increase was necessary to obtain the same final number of CFU at the site of infection as in the controls. It is concluded that granulocytes contributed substantially to antibiotic efficacy against S. aureus in this short-term infection model. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.