An 82-year-old woman presented to the emergency department with altered mental status thought to be due to complicated
cystitis and was treated with
TMP-SMX 160 mg/800 mg orally twice daily for 7 days. Her basic metabolic panel prior to initiation of
TMP-SMX was within normal limits, with the exception of her serum
sodium of 132 mmol/L (range 133-145 mmol/L). The day after completing her 7-day course of
TMP-SMX therapy the patient was evaluated by her primary care provider and another basic metabolic panel revealed a reduction in the serum
sodium to 121 mmol/L. The patient's serum
sodium concentrations increased to baseline 7 days after completion of the
TMP-SMX therapy, and remained normal until she was treated in the emergency department several months later for another presumed
urinary tract infection. She was again started on
TMP-SMX therapy empirically, and within several days her serum
sodium concentrations decreased from 138 mmol/L to a low of 129 mmol/L. The
TMP-SMX therapy was discontinued upon negative urine culture results and her serum
sodium increased to 134 mmol/L upon discharge. Based upon the Naranjo probability scale score of 9,
TMP-SMX was the probable cause of the patient's
hyponatremia.
CONCLUSION: