Abstract
Background: One common selective serotonin reuptake inhibitor (SSRI) used to treat depression and other mood disorders is fluoxetine. Hyponatremia, or low serum sodium levels, is one of the side effects of fluoxetine and other selective serotonin reuptake inhibitors (SSRIs), despite their effectiveness in reducing depressed symptoms. Regular monitoring of serum sodium levels is essential to prevent and manage these side effects.

Aim and Objectives: The objective of this study was to evaluate and compare the changes in serum sodium levels in patients with depression taking fluoxetine in different age groups (18–45, 46–70 years) and to evaluate the adverse effects between the two age groups.

Materials and Methods: This prospective observational study involved 110 depressed patients who were divided into two age groups, 18–45 and 46–70 years old, and who attended a psychiatric outpatient department at a tertiary care hospital. Before starting fluoxetine therapy as well as in the first and third weeks afterward, serum sodium levels were tested, and adverse effects were noted. Between the two age groups, serum sodium level changes and other side effects were compared.

Results: The serum sodium levels in the 46–70-year-old age group significantly dropped at the first and third weeks following therapy, whereas in the 18–45 year-old age group, the decrease in serum sodium levels occurred only after the 3rd week of therapy (P = 0.0005). At the 3rd week of therapy, 46–70-year-old serum sodium levels were substantially lower than those of 18–45-year-old patients (136.6 vs. 140.5, P = 0.0005), and only older patients had hyponatremia after the 1st and 3rd weeks of therapy. The P value is highly statistically significant (< 0.01).

Conclusions: Fluoxetine can lower serum sodium levels, which are more common and clinically evident in the 46–70-year age group than in the 18–45-year age group. In the first few weeks of fluoxetine medication, monitoring serum sodium levels is advised, especially for patients in the 46–70 age group.

Key words: Elderly; Fluoxetine; Electrolyte Imbalance; Syndrome of Inappropriate Antidiuretic Hormone