Trimethoprim-sulfamethoxazole-induced hyponatremia in an elderly lady with Achromobacter xylosoxidans pneumonia: Case report and insights into mechanism

Severe hyponatremia due to trimethoprim-sulfamethoxazole-induced SIADH

Hyponatremia, a serum sodium level of <135 mEq/L, is the most common electrolyte abnormality occurring in 5%–35% of hospitalized patients. It is a predictor of increased morbidity and mortality. Diuretics, psychotropic, and antiepileptic drugs are commonly implicated in drug-induced hyponatremia. Trimethoprim-sulfamethoxazole and spironolactone are two commonly prescribed drugs; unfortunately, most providers are unfamiliar with these two drugs causing hyponatremia. Simultaneous use of trimethoprim-sulfamethoxazole and spironolactone can cause serious drug interactions that increase the risk of hyponatremia, hyperkalemia, and overall mortality. Despite recommendations to avoid using these two drugs concurrently, many healthcare providers continue to prescribe them together. We report a case of an elderly female with severe hyponatremia caused by trimethoprim-sulfamethoxazole superimposed on a chronic but stable mild hyponatremia.

Analysis of the Clinical Characteristics of Hyponatremia Induced by Trimethoprim/Sulfamethoxazole

BACKGROUND

Trimethoprim-sulfamethoxazole (TMP/SMX) causes hyperkalemia, and hyponatremia caused by TMP/SMX is a challenge for clinicians. We described the clinical features of hyponatremia induced by TMP/SMX after collecting cases.

SUMMARY

The median age of the 24 patients (10 males and 14 females) was 67 years (range: 28-90 years). Hyponatremia induced by TMP/SMX manifested as nausea (41.7%) and vomiting (29.2%) or asymptomatic hyponatremia (20.8%). The median duration of hyponatremia was 5 days (range: 3-10 days). The median serum sodium concentration was 118 mmol/L (range: 101-128.1 mmol/L). The serum sodium levels gradually returned to the normal range at 4 days (median; range: 2-14 days) after withdrawing TMP/SMX.

KEY MESSAGES

TMP/SMX-induced hyponatremia is a rare and serious adverse reaction. Clinicians should be aware of electrolyte disturbances caused by TMP/SMX and should always consider electrolyte monitoring.