Decreased Linezolid Serum Concentrations in Three Critically Ill Patients: Clinical Case Studies of a Potential Drug Interaction between Linezolid and Rifampicin.

Linezolid is a valuable treatment option for treating infections caused by multi-resistant gram-positive pathogens. Lack of effective linezolid levels due to the co-administration of rifampicin has been described in healthy subjects. However, the clinical significance of this potential drug interaction (DI) for critically ill patients is still unclear. This was a retrospective analysis of 3 critically ill patients with the combination therapy of linezolid and rifampicin or rifampicin pre-treatment. Despite increasing the dose of linezolid, the majority of observed linezolid trough concentrations in all 3 patients were below 2 mg/l. Furthermore, linezolid trough concentrations remained below 2 mg/l after discontinuation of rifampicin. This potential DI between linezolid and rifampicin could lead to treatment failure. Therefore, we strongly recommend that linezolid serum concentrations be monitored in patients with rifampicin co-administration or rifampicin pretreatment.