Treatment Algorithms, Augmentation, and Treatment-Resistant Depression

Module 8 — Chapter 17: Antidepressant Drugs

Augmentation Strategies — Mechanism, Best-Fit Residual Symptom, and Key Caution
Agent Mechanism Rationale Best-Fit Residual Symptom Key Caution
Aripiprazole, Brexpiprazole Dopamine D2 partial agonism restores prefrontal dopaminergic tone; serotonin-1A partial agonism adds anxiolytic effect Anhedonia, low motivation, cognitive slowing, fatigue Weight gain (less than quetiapine); akathisia (more with aripiprazole); long-term tardive dyskinesia risk
Quetiapine (low dose) Serotonin-2A antagonism improves sleep; histamine H1 blockade adds sedation; dopamine blockade minimal at low doses Insomnia, residual anxiety, nighttime rumination Most weight gain of the atypical antipsychotic options; daytime sedation
Bupropion Adds norepinephrine and dopamine transporter inhibition to the selective serotonin reuptake inhibitor's serotonergic mechanism — addresses the catecholaminergic deficit Fatigue, hypersomnia, low motivation, anhedonia, sexual dysfunction Potent cytochrome P450 2D6 inhibitor — raises levels of co-administered selective serotonin reuptake inhibitors; lowers seizure threshold
Lithium Enhances serotonin synthesis and release; sensitizes postsynaptic serotonin-1A receptors; longest historical evidence base for augmentation Inadequate overall antidepressant response; no dominant residual symptom pattern Narrow therapeutic index; requires renal and thyroid monitoring; hydration-sensitive; drug interactions (lithium levels raised by thiazides, nonsteroidal anti-inflammatory drugs)
Buspirone Serotonin-1A partial agonism accelerates autoreceptor desensitization; anxiolytic without sedation or dependence Residual anxiety as dominant feature of partial response No dependence; no respiratory depression; onset delayed one to two weeks; may not add benefit in patients already on serotonin-1A-active agents
Triiodothyronine (T3) Thyroid hormone regulates central noradrenergic and serotonergic receptor sensitivity; subclinical hypothyroidism blunts antidepressant response Inadequate response in patients at low-normal thyroid function; fatigue-predominant presentation Monitor for hyperthyroid symptoms; preferred over thyroxine (T4) — no peripheral conversion required
Maintenance Therapy
Duration by Episode Count
  • First episode: Continue 6 to 12 months after remission, then gradual taper. Relapse risk ~50% if stopped early.
  • Second episode: Continue 2 years after remission before considering discontinuation. Recurrence risk ~70%.
  • Three or more episodes: Consider indefinite maintenance. Recurrence risk ~90% without maintenance.
  • Any severe or suicidal episode: Strong indication for indefinite maintenance regardless of episode count
  • Key rule: Same dose that produced remission — do not reduce during continuation phase
  • All tapering: Gradual, with follow-up within 4 to 8 weeks of dose reduction
Treatment-Resistant Depression
Rule Out Pseudo-Resistance First
  • Definition: Failure after two or more adequate trials of different classes at therapeutic doses
  • Confirm adequate dose and full trial duration for each prior antidepressant
  • Confirm adherence (plasma concentration measurement if available)
  • Assess for hypothyroidism, sleep apnea, substance use, chronic pain
  • Screen for bipolar disorder — antidepressant monotherapy may worsen bipolar depression
  • Somatic options once true treatment-resistant depression confirmed: esketamine; electroconvulsive therapy (most effective, 50 to 70 percent remission); transcranial magnetic stimulation (Food and Drug Administration-cleared after one failed trial)
STAR*D — The Core Message

Only one-third of patients achieve remission on the first antidepressant (Step 1: 37 percent; Step 2: 31 percent; Step 3: 14 percent; Step 4: 13 percent). This is the expected pharmacological reality. The response is a systematic sequential treatment strategy — with optimization at each step before switching — not reactive prescribing driven by frustration. Cumulative remission across all steps reached 67 percent.