# Severe Hyponatremia Secondary to Ciprofloxacin-Induced Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): A Case Report

## TL;DR

An elderly man developed severe low sodium levels due to a rare side effect of ciprofloxacin, highlighting the need for careful medication review.

## Contribution

This case report identifies ciprofloxacin as a rare but serious cause of SIADH-induced hyponatremia.

## Key findings

- Ciprofloxacin was linked to severe hyponatremia via SIADH in an 84-year-old patient.
- Discontinuation of ciprofloxacin and treatment with hypertonic saline normalized sodium levels.
- A Naranjo score of 7 confirmed a probable adverse drug reaction to ciprofloxacin.

## Abstract

Hyponatremia is a common electrolyte disturbance characterized by reduced serum sodium levels, which, when severe, can lead to life-threatening complications. Severe hyponatremia requires prompt treatment and thorough investigation in order to identify the underlying cause and correct the precipitating factor. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a cause of euvolemic hyponatremia, involving excessive release of antidiuretic hormone, which promotes renal water reabsorption. Ciprofloxacin, a fluoroquinolone antibiotic, is a rare cause of SIADH through the activation of central nervous system receptors involved in the antidiuretic hormone secretion. The authors report a case of an 84-year-old male with advanced dementia who presented to the emergency department with severe hyponatremia (serum sodium of 103 mmol/L). Diagnostic criteria for SIADH were fulfilled, and after exclusion of other causes of hyponatremia, recent ciprofloxacin exposure was recognized as the cause. Ciprofloxacin was discontinued, and treatment with hypertonic saline and fluid restriction resulted in gradual normalization of serum sodium levels without recurrence. A Naranjo score of 7 supported a probable adverse drug reaction to ciprofloxacin. This case highlights the importance of a systematic medication review in patients with severe hyponatremia and emphasizes that ciprofloxacin, despite being widely prescribed, can rarely induce life-threatening SIADH, warranting increased clinical awareness and prompt drug discontinuation.