7.1 Major Depressive Disorder & Anxiety Disorders

Major Depressive Disorder & Anxiety Disorders

Executive Summary: Major Depressive Disorder (MDD) and Generalized Anxiety Disorder (GAD) are ubiquitous, highly disabling psychiatric conditions managed extensively within ambulatory care practice. For the Board Certified Ambulatory Care Pharmacist (BCACP), mastering psychiatric pharmacotherapy requires precise application of validated diagnostic scoring instruments (PHQ-9, GAD-7), nuanced selection among first-line selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), tailored deployment of atypical antidepressants (bupropion, mirtazapine) based on patient-specific comorbidity phenotypes, execution of evidence-based switching and augmentation protocols for treatment-resistant depression, and rigorous stewardship of benzodiazepines to prevent dependence and withdrawal toxicity.

1. DSM-5-TR Diagnostic Criteria & PHQ-9 Staging for MDD

Under the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR), a formal diagnosis of Major Depressive Disorder requires the presence of at least 5 of the following 9 symptoms during the same 2-week period, representing a clear change from previous functioning. At least one of the symptoms must be either (1) Depressed mood or (2) Loss of interest or pleasure (Anhedonia).

The SIGECAPS Diagnostic Mnemonic

Exclusionary Rule: Symptoms must cause clinically significant distress or functional impairment and must not be attributable to the direct physiological effects of a substance (e.g., drug abuse, medication) or another medical condition (e.g., severe hypothyroidism, systemic lupus erythematosus). In addition, there must never have been a manic or hypomanic episode (which would redefine the diagnosis as Bipolar Disorder).

The Patient Health Questionnaire-9 (PHQ-9)

The PHQ-9 is a 9-item self-report questionnaire that scores each DSM-5-TR symptom from 0 (not at all) to 3 (nearly every day), yielding a total score between 0 and 27 points.

• Suicide Risk Item (Item 9): Question 9 specifically assesses thoughts of self-harm or being better off dead. Any positive score (1, 2, or 3) mandates an immediate, comprehensive suicide risk assessment (e.g., Columbia-Suicide Severity Rating Scale [C-SSRS]), evaluating intent, plan, lethality, and access to lethal means.
• Treatment Response & Remission Metrics:
  • Clinical Response: Defined as a ≥50% reduction in baseline PHQ-9 score.
  • Clinical Remission: Defined as achieving a PHQ-9 score < 5 points.

2. Selective Serotonin Reuptake Inhibitors (SSRIs): Comparative Clinical Pharmacology

SSRIs selectively block the presynaptic serotonin transporter (SERT / SLC6A4), increasing synaptic 5-HT concentrations in the somatodendritic and axon terminal regions of serotonergic neurons. They represent the universal first-line pharmacotherapy for MDD, GAD, Panic Disorder, OCD, and PTSD.

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|                                 SSRI COMPARATIVE PHARMACOTHERAPY MATRIX                                 |
+------------------+-----------------------+------------------------+-------------------------------------+
| Drug & Daily Dose| Primary Indications   | Half-Life & Kinetics   | Key Safety Nuances & Clinical Pearls|
+------------------+-----------------------+------------------------+-------------------------------------+
| **Sertraline**   | MDD, GAD, OCD, PTSD,  | Parent: ~26 hours      | **Cardiovascular Gold Standard:**   |
| (Zoloft)         | Panic, PMDD, SAD      | Active Metabolite:     | Drug of choice post-MI and in heart |
| 50–200 mg/day    |                       | N-desmethyl (~66 hours)| failure (SADHART trial). Frequent GI|
|                  |                       |                        | upset (take with meals/breakfast).  |
+------------------+-----------------------+------------------------+-------------------------------------+
| **Escitalopram** | MDD, GAD              | ~27–32 hours           | **Pure S-Enantiomer:** Highly       |
| (Lexapro)        |                       | Linear kinetics        | selective SERT inhibitor; minimal   |
| 10–20 mg/day     |                       |                        | CYP interactions; very well         |
|                  |                       |                        | tolerated. Max 10 mg/day in elderly.|
+------------------+-----------------------+------------------------+-------------------------------------+
| **Citalopram**   | MDD                   | ~35 hours              | **Strict FDA QTc Boxed Warning:**   |
| (Celexa)         |                       | Racemic (R/S) mixture  | Max 40 mg/day in adults; **Max 20   |
| 20–40 mg/day     |                       |                        | mg/day** if age >60, hepatic impair,|
|                  |                       |                        | CYP2C19 poor metabolizers, or with  |
|                  |                       |                        | CYP2C19 inhibitors (cimetidine).    |
+------------------+-----------------------+------------------------+-------------------------------------+
| **Fluoxetine**   | MDD, OCD, Panic,      | Fluoxetine: 1–3 days   | **Activating & Self-Tapering:**     |
| (Prozac)         | Bulimia, PMDD, Bipolar| Norfluoxetine: 7–15    | Longest half-life; lowest risk of   |
| 20–80 mg/day     | depression (with OFC) | days (CYP2D6 inhibitor)| discontinuation syndrome. Requires  |
|                  |                       |                        | **5-week washout** before MAOIs.    |
+------------------+-----------------------+------------------------+-------------------------------------+
| **Paroxetine**   | MDD, GAD, OCD, PTSD,  | ~21 hours              | **Anticholinergic & Teratogenic:**  |
| (Paxil, Pexeva)  | Panic, SAD, VMS       | Potent CYP2D6 inhibitor| Most sedating, anticholinergic, and |
| 20–50 mg/day     | (Brisdelle 7.5 mg)    | Non-linear kinetics    | weight-gain prone. Highest risk of  |
|                  |                       |                        | withdrawal; avoid in pregnancy (VSD)|
+------------------+-----------------------+------------------------+-------------------------------------+

Critical Class Adverse Effects & Safety Management

• Gastrointestinal Effects: Nausea, vomiting, diarrhea (mediated by stimulation of peripheral 5-HT3 and 5-HT4 receptors). Typically resolves within 1–2 weeks; counsel patients to take doses with food.
• Sexual Dysfunction: Decreased libido, erectile dysfunction, delayed ejaculation, and anorgasmia (mediated by 5-HT2A stimulation). Persists throughout therapy; manage by dose reduction, switching to bupropion or mirtazapine, or augmenting with sildenafil/tadalafil or bupropion.
• Hyponatremia / SIADH: Syndrome of Inappropriate Antidiuretic Hormone secretion occurs disproportionately in elderly patients, those on thiazide diuretics, or with low baseline volume. Monitor serum sodium within 2–4 weeks of initiation.
• Bleeding Risk: Platelets depend on SERT to take up serotonin necessary for platelet aggregation. SERT blockade increases the risk of upper GI bleeding, especially when co-prescribed with NSAIDs, aspirin, or oral anticoagulants (consider gastroprotection with a PPI).
• Bone Mineral Density Loss: Long-term SSRI use is associated with increased osteoporotic fracture risk.
• Antidepressant Discontinuation Syndrome (FINISH Mnemonic): Flu-like symptoms, Insomnia, Nausea, Imbalance (dizziness, vertigo), Sensory disturbances ("brain zaps", electric shock sensations), and Hyperarousal (anxiety, agitation). Most pronounced with short half-life agents lacking active metabolites (paroxetine, venlafaxine); least common with fluoxetine. Always taper gradually over 2–4+ weeks.

3. SNRIs, Bupropion, Mirtazapine, TCAs & MAOIs

Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

SNRIs inhibit both SERT and the norepinephrine transporter (NET / SLC6A2), elevating central 5-HT and NE. They are especially beneficial in patients with comorbid chronic pain, diabetic neuropathy, or fibromyalgia.

• Venlafaxine (Effexor XR: 75–225 mg/day):
  • Dose-Dependent Receptor Affinity: At low doses (<150 mg/day), venlafaxine acts almost exclusively as an SSRI. At doses ≥150 mg/day, NET inhibition becomes clinically significant.
  • Hemodynamic Impact: Dose-dependent increases in blood pressure (average 2–5 mmHg diastolic elevation) and heart rate. Baseline BP must be controlled prior to initiation, and blood pressure monitored regularly.
• Duloxetine (Cymbalta: 30–60 mg once daily, max 120 mg/day):
  • Balanced Dual Reuptake Inhibition: Potent SERT and NET inhibition across its full therapeutic dosing range.
  • Multispecialty FDA Indications: MDD, GAD, Diabetic Peripheral Neuropathic Pain (DPNP), Fibromyalgia, and Chronic Musculoskeletal Pain (low back pain, osteoarthritis).
  • Hepatic & Renal Restrictions: Strictly avoid in patients with substantial alcohol use, evidence of chronic liver disease, or severe renal impairment (CrCl < 30 mL/min).
• Desvenlafaxine (Pristiq: 50 mg once daily, max 100 mg/day): Active major metabolite of venlafaxine; eliminates reliance on CYP2D6 polymorphisms, providing consistent pharmacokinetics.

Norepinephrine-Dopamine Reuptake Inhibitor (NDRI): Bupropion

Bupropion inhibits the reuptake of norepinephrine (NET) and dopamine (DAT) without direct serotonergic activity.

• Clinical Advantages: Highly activating (energizing), promotes cognitive focus, weight neutral or promotes modest weight loss, and carries zero incidence of sexual dysfunction (frequently used as an antidote to SSRI-induced sexual dysfunction). Also FDA approved for smoking cessation under the trade name Zyban.
• Strict Boxed Warning & Contraindications — Seizure Risk:
  • Bupropion lowers the seizure threshold in a dose-dependent manner (incidence ~0.1% at ≤300 mg XL, rising to 0.4% at 450 mg XL).
  • Absolute Contraindications: (1) Active seizure disorder or history of seizures, (2) Current or prior diagnosis of Bulimia Nervosa or Anorexia Nervosa (high incidence of severe grand mal seizures due to electrolyte instability), (3) Abrupt discontinuation of alcohol, benzodiazepines, barbiturates, or antiepileptic drugs, (4) Co-administration with MAOIs (requires 14-day washout).
  • Maximum single dose for IR is 150 mg; maximum daily dose for XL is 450 mg/day.

Noradrenergic & Specific Serotonergic Antidepressant (NaSSA): Mirtazapine

Mirtazapine (Remeron: 15–45 mg once daily at bedtime) is an antagonist at central presynaptic alpha-2 adrenergic auto- and hetero-receptors, increasing noradrenergic and serotonergic transmission, while simultaneously blocking postsynaptic 5-HT2A, 5-HT2C, 5-HT3, and H1 histaminergic receptors.

• Inverse Dosing / Receptor Affinity Paradox:
  • Low Doses (7.5–15 mg/day): Potent H1-histamine receptor and 5-HT2C receptor antagonism dominate, producing intense sedation, increased appetite, and significant weight gain (highly advantageous for frail, underweight elderly patients with severe insomnia and cachexia).
  • Higher Doses (30–45 mg/day): Increased central noradrenergic transmission offsets H1 sedation, resulting in a more activating antidepressant profile with less somnolence.
• Safety Profile: Virtually zero sexual dysfunction (due to 5-HT2A blockade) and antiemetic properties (due to 5-HT3 blockade).

Tricyclic Antidepressants (TCAs) & Monoamine Oxidase Inhibitors (MAOIs)

Absolute Practice Rule — MAOI Washout Periods: Co-administration of MAOIs with serotonergic agents (SSRIs, SNRIs, TCAs, meperidine, tramadol, dextromethorphan, linezolid) precipitates fatal Serotonin Syndrome. A mandatory 14-day (2-week) washout is required when switching between an MAOI and other antidepressants. When switching from Fluoxetine to an MAOI, a 5-week (35-day) washout is mandatory due to the prolonged elimination half-life of fluoxetine and its active metabolite norfluoxetine.

4. Generalized Anxiety Disorder (GAD) & Benzodiazepine Stewardship

Generalized Anxiety Disorder (GAD) is characterized by excessive, uncontrollable worry and anxiety occurring more days than not for at least 6 months, accompanied by somatic symptoms (muscle tension, restlessness, fatigue, impaired concentration, irritability, sleep disturbance). Severity is tracked using the GAD-7 scale (0–4 minimal, 5–9 mild, 10–14 moderate, 15–21 severe).

First-Line Maintenance Pharmacotherapy for GAD

• SSRIs (Escitalopram, Sertraline, Paroxetine) & SNRIs (Duloxetine, Venlafaxine XR): Established first-line therapies providing long-term symptom control and preventing relapse without abuse liability.
  • Clinical Initiation Rule ("Start Low, Go Slow"): Patients with anxiety are hyper-sensitive to initial activating/jitteriness adverse effects. Initiate at half the standard starting dose for depression (e.g., escitalopram 5 mg daily, sertraline 25 mg daily, duloxetine 30 mg daily) for 1–2 weeks before titrating to full therapeutic target doses.
• Buspirone (BuSpar: 7.5 mg BID, titrate to 15–30 mg BID; max 60 mg/day):
  • Mechanism: High-affinity 5-HT1A presynaptic and postsynaptic partial agonist, providing anxiolysis without sedation, muscle relaxation, or anticonvulsant activity.
  • Zero Abuse Liability: Not a controlled substance; no physical dependence, tolerance, or withdrawal syndrome.
  • Pharmacokinetic Pearls: Must be taken consistently either with food or without food (food increases bioavailability 2-fold). Delayed onset of action (2 to 4 weeks); buspirone is completely ineffective as an acute as-needed (PRN) anxiolytic.

Benzodiazepines: Acute Crisis Bridging & Deprescribing Protocols

Benzodiazepines (lorazepam, clonazepam, alprazolam, diazepam) act as positive allosteric modulators of the GABAA receptor, increasing chloride channel opening frequency to produce immediate central nervous system depression.

+---------------------------------------------------------------------------------------+
|                      BENZODIAZEPINE AMBULATORY STEWARDSHIP RULES                      |
+------------------------------------+--------------------------------------------------+
| Clinical Domain                    | Mandatory Ambulatory Practice Rule               |
+------------------------------------+--------------------------------------------------+
| Role in GAD / Panic Therapy        | Strictly restricted to **short-term acute crisis  |
|                                    | management (1 to 2 weeks)** or as a brief bridge |
|                                    | while initiating an SSRI/SNRI.                   |
+------------------------------------+--------------------------------------------------+
| Geriatric Safety (Beers Criteria)  | **Avoid in older adults (Age >= 65)** due to high|
|                                    | risk of cognitive impairment, delirium, motor    |
|                                    | incoordination, falls, and hip fractures.        |
+------------------------------------+--------------------------------------------------+
| FDA Boxed Warning with Opioids     | Co-prescribing opioids and benzodiazepines       |
|                                    | produces profound sedation, respiratory          |
|                                    | depression, coma, and fatal overdose.            |
+------------------------------------+--------------------------------------------------+
| Withdrawal Seizure Risk            | Abrupt cessation of chronic benzodiazepines      |
|                                    | triggers severe autonomic hyperactivity, rebound |
|                                    | anxiety, delirium tremens, and status epilepticus|
+------------------------------------+--------------------------------------------------+
| Guideline Deprescribing Taper      | **Slow Stepwise Taper:** Reduce total daily dose |
|                                    | by **10% to 25% every 1 to 2 weeks** over several|
|                                    | months. Convert short-acting agents (alprazolam) |
|                                    | to long-acting agents (clonazepam, diazepam)     |
|                                    | if withdrawal symptoms emerge during tapering.   |
+------------------------------------+--------------------------------------------------+