In vitro testing of daptomycin plus rifampin against methicillin-resistant Staphylococcus aureus resistant to rifampin.
OBJECTIVE
To test for synergy between daptomycin (DAP) and rifampin (RIF) against RIF-resistant methicillin-resistant Staphylococcus aureus (MRSA) isolates.


METHODS
Synergy testing using time-kill assay (TKA) was performed on 6 clinically, and genetically unique RIF-resistant MRSA isolates. The isolates were identified out of 489 (1.2%) samples collected during April 2003 to August 2006, from patients at the Ochsner Medical Center in New Orleans, Louisiana, United States of America.


RESULTS
Synergy testing of DAP plus RIF by TKA showed that 5 isolates were indifferent, but one isolate was antagonistic.


CONCLUSIONS
Our in vitro study failed to demonstrate synergy between DAP plus RIF, against our RIF-resistant MRSA isolates. Clinical failure of this combination should prompt the clinician to consider antagonism, as one of the potential causes.
Khasawneh
Faisal A
FA
Department of Internal Medicine, King Hussein Cancer Center, Amman, Jordan, and formerly of Tulane Health Sciences Center, New Orleans, Louisiana, United States of America.
Ashcraft
Deborah S
DS
Pankey
George A
GA
D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D017576:Daptomycin / Q000008:administration & dosage*; D004359:Drug Therapy, Combination; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus; D012293:Rifampin / Q000008:administration & dosage*; D013203:Staphylococcal Infections / Q000188:drug therapy*
D000900:Anti-Bacterial Agents; D017576:Daptomycin; D012293:Rifampin