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Canadian Pharmacist Qualifying Exam Practice · Question

A 35-year-old female is started on an antidepressant that selectively inhibits the reuptake of serotonin in the brain. Her doctor informs her that it will take approximately 2-4 weeks to experience the full therapeutic effect. This delay is primarily due to:

While steady-state concentrations are usually reached within 4-5 half-lives, the full therapeutic effect of SSRIs typically takes longer (2-4 weeks). This delay

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Question: A 35-year-old female is started on an antidepressant that selectively inhibits the reuptake of serotonin in the brain. Her doctor informs her that it will take approximately 2-4 weeks to experience the full therapeutic effect. This delay is primarily due to:

Answer options:

  • Slow absorption of the drug from the gastrointestinal tract. ✅ The time required for down-regulation or desensitization of postsynaptic serotonin receptors.
  • The need for the drug to reach steady-state plasma concentrations.
  • Its extensive first-pass metabolism in the liver.

Correct answer: The time required for down-regulation or desensitization of postsynaptic serotonin receptors.

Explanation: While steady-state concentrations are usually reached within 4-5 half-lives, the full therapeutic effect of SSRIs typically takes longer (2-4 weeks). This delay is thought to be due to adaptive changes in receptor sensitivity and intracellular signaling pathways, specifically the desensitization of autoreceptors and increased postsynaptic receptor activity.

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