Hyponatremia Associated with QuinupristinDalfopristin

TO THE EDITOR: Quinupristindalfopristin has recently been released for treatment of infection with gram-positive organisms, such as vancomycin-resistant Enterococcus faecium. We report the development of marked hyponatremia associated with this drug. A 67-year-old woman with peripheral neuropathy, IgM paraproteinemia, and tobacco-related chronic obstructive pulmonary disease was hospitalized with dyspnea and hyponatremia. Chest radiography showed collapse of the right middle and lower lobes. Bronchoscopy revealed small-cell carcinoma occluding the bronchus intermedius. The patient received three cycles of chemotherapy with etoposide, cyclophosphamide, and adriamycin. Her hospital course was notable for three episodes of nadir sepsis, prolonged ventilator dependence, and depression (treated with sertraline). On hospital day 95, she developed neutropenia-related fever and hypotension. Ceftazidime and vancomycin were started along with intravenous fluids and norepinephrine. On hospital day 103, therapy with quinupristindalfopristin, 7.5 mg/kg of body weight every 8 hours, was begun because a blood culture grew vancomycin-resistant E. faecium. During quinupristindalfopristin administration, the serum sodium level decreased (Figure). On hospital day 110, the serum osmolarity was 268 mosm/L and the urine osmolarity was 426 mosm/L. Quinupristindalfopristin therapy was discontinued on hospital day 111, and the sodium level gradually returned to baseline value. Repeated blood cultures were negative for bacterial growth. Figure. Serum sodium level before, during, and after quinupristin dalfopristin treatment. The hyponatremia was probably secondary to inappropriate secretion of antidiuretic hormone. Small-cell carcinoma has been associated with hyponatremia. Our patient had responded to chemotherapy, however, and repeated bronchoscopy showed disappearance of the original mass. Hyponatremia did not develop during earlier cyclophosphamide treatment. Sertraline has been associated with hyponatremia (1), but in this case the hyponatremia worsened after this drug was withdrawn and it continued to improve after reinstitution of the drug. The increasing incidence of vancomycin-resistant E. faecium infections in hospitalized patients and the limited options for treatment suggest that use of quinupristindalfopristin in this population will increase. Development of hyponatremia in this setting should alert the physician to a possible adverse effect related to this drug.