A 52-year-old man presents with depressed mood for 8 months. He reports passive death wishes but no active suicidal plan. His appetite is decreased and he has lost 4 kg. He denies any prior manic or hypomanic episodes. His PHQ-9 score is 19. His thyroid-stimulating hormone is 9.2 mIU/L (normal 0.4–4.0). Levothyroxine is initiated. After 6 weeks of adequate thyroid replacement, depressive symptoms persist. Which antidepressant class should be avoided due to its potential to worsen hypothyroidism-associated cardiac conduction?

• A Selective serotonin reuptake inhibitors (SSRIs)
• B Serotonin-norepinephrine reuptake inhibitors (SNRIs)
• C Tricyclic antidepressants (TCAs) ✓
• D Mirtazapine

Explanation

Tricyclic antidepressants prolong the QTc interval and can worsen pre-existing conduction abnormalities, which are more prevalent in hypothyroidism due to bradycardia and conduction slowing. SSRIs and SNRIs are the preferred first-line agents in this context. Mirtazapine is generally well tolerated. TCAs also lower the seizure threshold and carry significant anticholinergic burden, further limiting their use in medically complex patients.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.