Synergic activity of imipenem/cilastatin combined with cefotiam against methicillin-resistant Staphylococcus aureus.

The synergic activity of imipenem/cilastatin combined with cefotiam was studied in a mouse bacteraemia model. Combinations of imipenem plus cefotiam in ratios from 1:5 to 1:160 were more effective than either imipenem alone or cefotiam alone (P < 0.05). Synergy was observed against both beta-lactamase producing and beta-lactamase non-producing MRSA. Staggered combinations of imipenem with cefotiam (each drug was administered at a different time) were studied in an in-vitro pharmacokinetic system to clarify relationships between killing kinetics and pharmacodynamics of the combinations. In the in-vitro system, cefotiam (1 g over 30 min) administered 2 h after imipenem administration (250 mg over 30 min) reduced viable cell counts to an undetectable level and maintained this for 4 h, while the simultaneous administration of imipenem and cefotiam maintained an undetectable cell count for only 2 h. Furthermore, imipenem administered after cefotiam showed no synergy. These results indicate that the timing of dosing of each antibiotic influences synergy, and administration of cefotiam 2 h after imipenem is more effective than the other regimens.