Drug Interaction Between Citalopram and Sertraline

Mechanism of Interaction

The American Academy of Child and Adolescent Psychiatry recommends that citalopram and sertraline should not be used concurrently due to the risk of serotonin syndrome, a potentially life-threatening condition 1, 2
Combining two serotonergic medications, such as citalopram and sertraline, significantly increases the risk of serotonin syndrome due to excessive serotonin accumulation in the central nervous system 1, 2

Serotonin syndrome typically develops within 24-48 hours of combining serotonergic medications and presents with mental status changes, such as confusion, agitation, and anxiety 1
The syndrome also presents with neuromuscular hyperactivity, including tremors, clonus, hyperreflexia, and muscle rigidity 1
Autonomic hyperactivity, including hypertension, tachycardia, arrhythmias, tachypnea, diaphoresis, shivering, vomiting, and diarrhea, is also a symptom of serotonin syndrome 1
Advanced symptoms of serotonin syndrome include fever, seizures, arrhythmias, and unconsciousness, which can be potentially fatal 1, 2

Citalopram has less effect on CYP450 isoenzymes compared to other SSRIs, but this does not mitigate the serotonergic effects when combined with sertraline 1
The primary concern with combining citalopram and sertraline is not the metabolic interaction, but the additive serotonergic effects 1, 2

The American Academy of Child and Adolescent Psychiatry recommends that citalopram and sertraline should never be combined due to the high risk of serotonin syndrome 1, 2
When switching between these medications, a washout period based on the half-life of the medication being discontinued should be allowed, with sertraline requiring approximately 1-2 weeks washout 2
If serotonin syndrome occurs, treatment includes immediate discontinuation of all serotonergic agents and hospital-based supportive care with continuous cardiac monitoring 1
Patients on either citalopram or sertraline should be cautioned against taking over-the-counter medications containing serotonergic compounds, such as St. John's wort or dextromethorphan 1

Even when switching from one SSRI to another, there is a risk of interaction if adequate washout time is not observed, as recommended by the American Academy of Child and Adolescent Psychiatry 2