Drug Interactions between Bethkis and daptomycin

Coadministration of daptomycin and tobramycin may alter the plasma concentrations of both drugs. The mechanism of interaction is unknown. In six healthy adult volunteers given a single 2 mg/kg IV dose of daptomycin and a 1 mg/kg IV dose of tobramycin, the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of daptomycin increased by 12.7% and 8.7%, respectively, compared to administration of the drug alone. Tobramycin Cmax and AUC decreased by 10.7% and 6.6%, respectively, during coadministration with daptomycin relative to administration alone. These differences were not statistically significant. However, the interaction between tobramycin and a clinical dose of daptomycin (4 mg/kg) has not been studied. Daptomycin package labeling recommends caution during coadministration with tobramycin.