A young man on a tricyclic antidepressant develops hot, red skin and urinary retention. This is best explained by which pharmacologic effect of TCAs?

A young man on a tricyclic antidepressant develops hot, red skin and urinary retention. This is best explained by which pharmacologic effect of TCAs?

• A. Anticholinergic effects
• B. Serotonin reuptake inhibition
• C. GABA receptor antagonism
• D. NMDA receptor antagonism

Answer: (A)

Muscarinic receptor blockade by TCAs causes anticholinergic toxicity, which best explains these findings. Blocking muscarinic receptors reduces sweating, so heat cannot dissipate efficiently, leading to hot, flushed skin. It also relaxes the detrusor muscle in the bladder, producing urinary retention. Serotonin reuptake inhibition would mainly affect mood and central serotonin-related effects, not produce urinary retention and heat intolerance. GABA receptor antagonism and NMDA receptor antagonism are not typical actions of TCAs and wouldn’t account for these specific signs.

Muscarinic receptor blockade by TCAs causes anticholinergic toxicity, which best explains these findings. Blocking muscarinic receptors reduces sweating, so heat cannot dissipate efficiently, leading to hot, flushed skin. It also relaxes the detrusor muscle in the bladder, producing urinary retention. Serotonin reuptake inhibition would mainly affect mood and central serotonin-related effects, not produce urinary retention and heat intolerance. GABA receptor antagonism and NMDA receptor antagonism are not typical actions of TCAs and wouldn’t account for these specific signs.