Older Adults May Have Low Blood Sodium Levels When Using the Antidepressant Venlafaxine (EFFEXOR)

This side effect has also been found with other drugs in the SSRI antidepressant family such as fluoxetine (PROZAC) or paroxetine (PAXIL).

Elderly patients should have sodium levels in their blood checked promptly and regularly if they are taking the antidepressant venlafaxine (EFFEXOR), according to a prominent Australian medical journal. 

In a May 2007 article, Australian researchers describe their study of 58 consecutive patients over the age of 65 in one doctor’s practice. The study was meant to determine how often patients using venlafaxine experienced low blood sodium (hyponatremia). Of the 58 patients, 10 (17.2 percent) developed hyponatremia. Of these 10 patients, five were excluded from prolonged (six-month) observation because of severe medical illness, other side effects from the antidepressant or being lost to follow-up.

Typically, low blood sodium developed within the first few days of starting treatment with venlafaxine. Patients were able to return their sodium levels to normal by restricting daily fluid intake. Patients who experienced this side effect and then restricted fluid intake remained well during the six-month follow-up period after their diagnosis of low sodium and were able to continue their medication during this time under close observation.

The authors of the study concluded that:

Patients [older than] 65 years of age should have their electrolytes [chemicals in the blood including sodium] measured 3-5 days after starting venlafaxine therapy. If hyponatremia develops, it can be managed with modest fluid restriction without discontinuing drug treatment, subject to close continued clinical observation and biochemical monitoring.

Common symptoms of low blood sodium include appetite loss, nausea, vomiting, headache, restlessness, fatigue, irritability, abnormal mental status (such as coma, hallucinations, confusion and decreased consciousness), convulsions, muscle weakness and muscle spasms or cramps. Low sodium and these same symptoms can also be caused by other antidepressants in the Selective Serotonin Reuptake Inhibitor family, such as fluoxetine (PROZAC) and paroxetine (PAXIL).

What You Can Do
Patients over the age of 65 taking or considering taking venlafaxine should ask their provider to check for low blood sodium levels within three to five days after treatment is started.

Patients taking venlafaxine who are experiencing the symptoms of low blood sodium levels listed above should contact the prescriber as soon as possible.

Patients should not discontinue taking venlafaxine without first consulting with their prescribing health care provider.