A 46-year-old female accountant is referred to the outpatient psychiatry clinic due to an … — USMLE Step 2 CK

A 46-year-old female accountant is referred to the outpatient psychiatry clinic due to an 8-month history of excessive, uncontrollable worry regarding her finances, job security, and health. She describes feeling constantly "on edge," suffers from severe muscle tension in her neck and shoulders, and struggles with initial insomnia. These symptoms began shortly after she underwent a lumpectomy and localized radiation for estrogen receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. She is currently taking tamoxifen and frequently complains of bothersome, spontaneous hot flashes occurring both during the day and at night. Vital signs are within normal limits. Which of the following is the most appropriate pharmacotherapy for this patient's psychiatric condition?

VenlafaxineAnswer
B
Paroxetine
C
Fluoxetine
D
Bupropion
E
Duloxetine

Answer

The correct answer is Venlafaxine.

This patient meets the DSM-5 criteria for Generalized Anxiety Disorder (GAD), presenting with more than 6 months of excessive worry associated with feeling "on edge," muscle tension, and insomnia. Furthermore, she is experiencing tamoxifen-induced vasomotor symptoms (hot flashes). Venlafaxine, a serotonin-norepinephrine reuptake inhibitor (SNRI), is the ideal choice. It is a first-line pharmacotherapy for GAD and is highly efficacious in reducing both the frequency and severity of vasomotor symptoms. Most importantly, venlafaxine exerts minimal to no inhibitory effect on the cytochrome P450 2D6 (CYP2D6) enzyme. Tamoxifen is a prodrug that requires activation by CYP2D6 to form its highly active metabolite, endoxifen. Therefore, venlafaxine safely treats both her GAD and hot flashes without compromising the efficacy of her breast cancer adjuvant therapy.

Step-by-Step Solution

Diagnose the primary psychiatric condition based on the clinical presentation.

The patient has Generalized Anxiety Disorder (GAD), characterized by >6 months of excessive worry and at least 3 somatic symptoms (feeling on edge, muscle tension, insomnia).

Establishing the diagnosis determines the appropriate class of psychiatric medications (SSRIs or SNRIs).

Identify concurrent medical conditions and active pharmacological treatments.

The patient has a history of ER-positive breast cancer, is actively taking tamoxifen, and suffers from severe vasomotor symptoms (hot flashes).

Psychiatric medication selection must account for drug-drug interactions and aim to treat comorbid symptoms if possible.

Analyze the metabolic pathway of tamoxifen and the interaction profiles of potential psychotropics.

Tamoxifen is a prodrug requiring activation by the hepatic enzyme CYP2D6 to its active metabolite, endoxifen. Strong CYP2D6 inhibitors must be avoided.

Inhibiting CYP2D6 reduces the oncologic efficacy of tamoxifen, significantly increasing the risk of cancer recurrence.

Select the optimal agent that treats GAD, alleviates hot flashes, and lacks CYP2D6 inhibition.

Venlafaxine is selected because it is first-line for GAD, highly effective for vasomotor symptoms, and has minimal to no CYP2D6 inhibitory effects.

This single agent safely addresses both her psychiatric and somatic complaints without compromising her breast cancer treatment.

Key Concept

In patients taking tamoxifen, the management of Generalized Anxiety Disorder (GAD) and vasomotor symptoms requires the selection of an SSRI/SNRI with minimal CYP2D6 inhibition (e.g., venlafaxine, escitalopram) to avoid blocking the conversion of tamoxifen into its active metabolite, endoxifen.

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