Antidepressant Poisoning

Basics

Antidepressants are the most commonly prescribed psychiatric medications in U.S.
Patients who overdose on antidepressants may be on various antidepressants, divided into SSRIs, SNRIs, and atypical. Concomitant usage of atypical antipsychotics and mood-stabilizing medications, some of which are FDA approved for the treatment of depressive disorders, is common
Antidepressants may be prescribed for multiple other indications, including chronic pain syndromes, anxiety, eating disorders, substance abuse, and sleep disorders
Tricyclic antidepressants (TCAs) are covered in a separate chapter

Mechanism

SSRIs:
- Increase serotonin at the synapse by preventing the reuptake of serotonin by the presynaptic neuron
- SSRIs include paroxetine, fluoxetine, sertraline, citalopram, and escitalopram
SNRIs:
- Similar to SSRIs, but also inhibit reuptake of norepinephrine
- Developed because said to have fewer side effects than SSRIs at therapeutic dose, although not true for toxicity
- SNRIs include venlafaxine, desvenlafaxine, and duloxetine
Atypical antidepressants:
- Have variable effects on serotonin, norepinephrine, and dopamine
- Include mirtazapine, trazodone, and bupropion
Atypical antipsychotics:
- Most antipsychotics have activity at dopamine receptors, although variable agonism/antagonism depending on medication and dopamine receptor
- Additional activity at serotonin, α-adrenergic, histamine, and muscarinic receptors
Psychiatric medications also have variable potassium and sodium channel blockade, leading to cardiotoxicity (QT and QRS prolongation, respectively)

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