Purpose: A possible case of moxifloxacin-induced syndrome of inappropriate antidiuretic hormone (SIADH) is reported.
Summary: A 66-year-old Caucasian woman with stage II chronic obstructive pulmonary disease (COPD) arrived at the emergency department from an outpatient clinic complaining of worsening shortness of breath, headache, body aches, and dizziness. Five days before her arrival at the hospital, the patient was seen in an outpatient clinic with symptoms of COPD exacerbation and was given a corticosteroid taper of prednisone 40 mg daily and moxifloxacin 400 mg daily. The patient was hospitalized, and her serum sodium concentration was 110 meq/L. Moxifloxacin was continued on admission, and the patient was admitted to the intensive care unit for frequent neurologic examination, serial serum sodium measurements, and fluid restriction. Her laboratory test results were consistent with SIADH. Fluid restriction at 1 L/day initially corrected her serum sodium concentration to 119 meq/L, but increases in serum sodium plateaued by day 2 of admission (119-122 meq/L). Moxifloxacin was discontinued on hospital day 3. At discharge, on hospital day 5, her serum sodium concentration had increased to 131 meq/L. She was restarted on her home medications and followed up in an outpatient clinic one week later. After multiple etiologies were ruled out, drug-induced SIADH associated with moxifloxacin was the most likely diagnosis for this patient. Clinicians should be aware of this potential adverse drug effect when assessing patients with hyponatremia or SIADH.
Conclusion: A 66-year-old woman developed severe hyponatremia after receiving moxifloxacin for five days for treatment of COPD exacerbation.