Overdoses with SSRIs alone cause sedation and usually have a good outcome with supportive care.
Serious toxicity and death can occur when SSRIs are taken in combination with MAOIs or tricyclic antidepressants (see Serotonin Toxicity).
Seizures have been reported and are significantly more common with SNRI overdosage.
In most cases CNS depression will predominate.
Treatment is supportive.
Serotonin Toxicity
May occur with combinations of drugs such as MAOIs with SSRIs, SNRIs, clomipramine, other tricyclic antidepressants, lithium, pethidine, tramadol.
The Hunter Serotonin Toxicity Criteria are used to diagnose serotonin toxicity. Diagnosis requires a combination of the above drugs, or the increase in dosage of serotonergic drug plus any three of the following clinical signs - agitation, diaphoresis, diarrhoea, fever, hyper-reflexia, mental status changes, myoclonus, shivering, tremor, incoordination - in the absence of any recent addition or increase in dosage of a neuroleptic agent (see TOXINZ for criteria).
Serotonin toxicity is usually mild and transient. Treatment is supportive. Diazepam is first line for agitation.
Hyperthermia above 38.5ºC indicates serious toxicity and may herald the onset of multiorgan failure. Treatment for hyperthermia needs to be aggressive and will usually involve active cooling, intubation and paralysis.
Seizures can occur with citalopram and escitalopram. Dose dependent QT prolongation can occur. Torsades de pointes (TdP) has been reported in rare cases. Those at higher risk of arrhythmia are patients taking a large overdose (>600 mg), or those with congenital QT prolongation, pre-existing heart conditions or >60 years old. Cardiac monitoring may be required. Consult a Specialist for advice if a patient has risk factors for serious toxicity. Use the QT nomogram to assess risk.