A possible interaction between linezolid and digoxin: A case report of therapeutic drug monitoring.

Drug-drug interactions lead to altered clinical effects, including adverse reactions. Therapeutic drug monitoring of digoxin is necessary due to its narrow therapeutic range. Linezolid can cause variable exposures in patients hospitalized in the intensive care unit owing to its possibility of drug-drug interactions. We present a patient with pneumonia and heart failure who experienced a possible drug interaction between linezolid and digoxin, resulting in high serum concentrations of both drugs. Also, the patient developed thrombocytopenia likely related to linezolid. The linezolid dose required to maintain sufficient levels had to reduce to 50% of the usual linezolid dose. A quarter dose of the standard digoxin dose was needed. Although the underlying mechanism of the drug interaction is unclear, we recommend conducting therapeutic drug monitoring when linezolid and digoxin are administered concurrently.