SHM Converge Scientific Abstract ePoster Gallery-From One Pickle to Another: Trimethoprim-Sulfamethoxazole Induced Hyponatremia

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This case describes an 87-year-old woman who developed symptomatic hyponatremia three days after starting trimethoprim-sulfamethoxazole (TMP-SMX) for a urinary tract infection. On presentation, she had malaise and laboratory findings consistent with hypotonic hyponatremia: sodium 120 mmol/L, serum osmolality 253 mOsm/kg, urine sodium 34 mmol/L, urine osmolality 201 mOsm/kg, and low bicarbonate at 18 mmol/L. Because TMP-SMX can cause renal salt wasting, the drug was stopped and she received 500 mL of normal saline. Her sodium improved to 128 mmol/L within 29 hours and her symptoms resolved.<br /><br />The discussion explains that trimethoprim acts similarly to potassium-sparing diuretics such as amiloride and triamterene by blocking the epithelial sodium channel (ENaC) in the collecting duct. This leads to natriuresis, volume depletion, and hyponatremia from salt wasting. It can also reduce potassium secretion, causing hyperkalemia, and may contribute to metabolic acidosis through impaired ammoniagenesis.<br /><br />TMP-SMX–induced salt wasting can look very similar to syndrome of inappropriate antidiuretic hormone secretion (SIADH), since both may present with high urine sodium and concentrated urine. However, the two conditions require opposite treatment: salt wasting needs saline-containing fluids, while SIADH is treated with fluid restriction. Recognizing the difference is essential, because giving fluid restriction to a salt-wasting patient can worsen hyponatremia, while giving saline to SIADH may be ineffective.

Asset Subtitle

Alexander A. Mc Daid

Meta Tag

Author List Aaron Stern, Alexander A. Mc Daid, Eduardo Ribas, Franklin Liu, Juan Luis Quintana Ruiz, Shakthi Raman, Surbhi Agrawal

Category Clinical Vignettes

Concept Trimethoprim-sulfamethoxazole

Concept Hyponatremia

Concept Renal Salt Wasting

Concept Salt Wasting Nephropathy

Concept ENaC

Distinguished Non-Finalist

Presenter Organization Department of Medicine, NYC Health + Hospitals / Elmhurst, Icahn School of Medicine at Mount Sinai

Presenting Author Alexander A. Mc Daid

Track Adult

Keywords

trimethoprim-sulfamethoxazole

hyponatremia

renal salt wasting

epithelial sodium channel

ENaC blockade

urinary tract infection

hypotonic hyponatremia

SIADH

hyperkalemia

metabolic acidosis

Trimethoprim-sulfamethoxazole

Hyponatremia

Renal Salt Wasting

Salt Wasting Nephropathy

ENaC