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psych.serotonin-syndrome.v1PRODUCTION
psych.serotonin-syndrome.v1

Serotonin syndrome — toxidrome from serotonergic exposure (Hunter 2003 PMID 12925718; Boyer NEJM 2005 PMID 15784664); STOP serotonergic + benzo + cyproheptadine + cooling; severe → ICU + intubation + paralysis (rocuronium); AVOID bromocriptine + succinylcholine

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12/12 authored

Canonical 12-phase frame with authored status for this dossier.

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Detailed

Serotonin syndrome = drug-induced toxidrome from excess 5-HT2A agonism via serotonergic monotherapy or polypharmacy (SSRI/SNRI/MAOI/linezolid/methylene blue/tramadol/triptan/fentanyl/DXM/MDMA/St John's wort/5-HTP/lithium augmentation). Triad = autonomic instability + neuromuscular hyperactivity (clonus dominant) + AMS. Diagnosis via Hunter Serotonin Toxicity Criteria 2003 (sens 84% spec 97%) preferred over Sternbach 1991. Pharmacology pivot: STOP all serotonergic agents IMMEDIATELY; BENZODIAZEPINE FIRST for sympatholysis + neuromuscular control + sedation; cyproheptadine (5-HT2A antagonist) for moderate-severe disease; cooling for hyperthermia; AVOID bromocriptine (pro-serotonergic, reserved for NMS), succinylcholine (rhabdo hyperK), droperidol / haloperidol (QTc + dopaminergic worsening), routine dantrolene (limited SS evidence) (Boyer NEJM 2005 PMID 15784664).

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SS diagnosis confirmed by Hunter criteria + serotonergic exposure documented (Dunkley QJM 2003 PMID 12925718)

Patient inputs (19)

Geriatric + serotonergic polypharmacy = highest SS risk (tramadol + SSRI common in elderly); paediatric out-of-scope (peds.serotonin-syndrome.v1 future)

Pregnancy on SSRI presenting with SS — STOP SSRI + supportive + reproductive psychiatry consult; sertraline preferred per APA 2023 if continuation post-recovery needed

Full medication reconciliation incl. OTC (dextromethorphan, St John's wort), supplements (5-HTP, L-tryptophan), illicit (MDMA, cocaine), recently discontinued (MAOI 14-d washout; fluoxetine 5-wk washout), and intraoperative (methylene blue) — mandatory for diagnosis (Hunter criteria gate; Boyer NEJM 2005)

Hunter criterion 1 cornerstone — spontaneous clonus = SS; inducible clonus + agitation/diaphoresis = SS; ocular clonus + agitation/diaphoresis = SS (Dunkley QJM 2003 PMID 12925718)

Hyperreflexia (lower > upper extremity), tremor, rigidity (severe) — distinguish from NMS (lead-pipe rigidity + hyporeflexia) (Boyer NEJM 2005)

Agitation / confusion / coma in severe SS — discriminator from NMS (stupor / mutism / catatonic) (Boyer NEJM 2005)

Diaphoresis + mydriasis + diarrhoea + hyperactive bowel sounds — distinguish from NMS (normal pupils + no diarrhoea) (Boyer NEJM 2005)

QTc baseline before any benzo / antiemetic / sedative; QTc prolongation risk from serotonergic + antiemetic combinations; baseline for droperidol AVOID decision

Rhabdomyolysis common in severe SS (neuromuscular hyperactivity + hyperthermia); CK > 5000 → aggressive IV fluids + alkalinization

Rhabdomyolysis-AKI risk; drives fluid + dose adjustment for renal-cleared agents; eGFR baseline

Electrolyte derangement (hyperK in rhabdo-AKI, hyperNa from diaphoresis dehydration) + acid-base (lactic acidosis if severe)

Baseline + leukocytosis common in severe SS; rule out infection differential

Urine drug screen mandatory — illicit serotonergic co-ingestants (MDMA / cocaine / DXM) common in young-adult presentations; informs trigger drug identification

T > 38°C with ocular / inducible clonus = Hunter criterion 5 (severe); T > 41°C = life-threatening — ICU + intubation + paralysis + aggressive cooling (Boyer NEJM 2005)

Sinus tachycardia universal in moderate-severe SS; > 120 with HTN drives benzo escalation (Boyer NEJM 2005)

Hypertension common in moderate-severe SS from sympathetic surge; SBP > 180 + serotonergic exposure → routes to cardio.hypertensive-emergency.serotonin-syndrome-related.v1 sister dossier

Component of MAP; DBP > 120 supports crisis criterion + autonomic severity

Hepatic clearance baseline; serotonergic agents are CYP-metabolised; rule out hepatic encephalopathy differential

Hyperthermia + neuromuscular activity → lactate elevation; tracks severity + response to cooling / paralysis

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (10)

10 need judgement
  • informationallife_threateningsevere_serotonin_syndrome_with_hyperthermia
    Severe SS with hyperthermia > 41°C + rigidity + rhabdomyolysis + multi-organ involvement OR refractory autonomic instability — life-threatening; ICU + intubation + paralysis (rocuronium, AVOID succinylcholine) + active cooling + benzo infusion + cyproheptadine NG (Boyer NEJM 2005 PMID 15784664)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningnms_overlap_differential
    NMS (Neuroleptic Malignant Syndrome) converging differential — antipsychotic exposure within 1-2 weeks + lead-pipe rigidity (NOT clonus) + hyporeflexia + stupor / mutism (NOT agitation) + hyperthermia + autonomic instability + ↑↑ CK (often > 10× normal) + days-weeks onset (Strawn AJP 2007; Caroff + Mann 1993). Treatment DIFFERS critically — bromocriptine 2.5 mg PO/NG TID + dantrolene 1-2.5 mg/kg IV q 6 h for NMS, NOT for SS (bromocriptine is pro-serotonergic and WORSENS SS) — the key NMS-vs-SS pharmacological pivot
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveremoderate_serotonin_syndrome
    Moderate SS — T 38-40°C + clonus + agitation + persistent autonomic features after initial benzo; treatment: discontinue all offending agents + benzo IV + cyproheptadine 12 mg PO load → 2 mg PO q 2 h + monitor (Boyer NEJM 2005 PMID 15784664; Gillman Pharmacother 2010 PMID 20429837)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverehunter_criteria_positive
    Hunter Serotonin Toxicity Criteria positive (Dunkley QJM 2003 PMID 12925718; sens 84%, spec 97%) — serotonergic agent exposure + ONE of: spontaneous clonus / inducible clonus + agitation OR diaphoresis / ocular clonus + agitation OR diaphoresis / tremor + hyperreflexia / hypertonia + T > 38°C + ocular OR inducible clonus — diagnostic gate
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverepolypharmacy_serotonergic_combinations
    Patient on multiple serotonergic agents simultaneously — most commonly SSRI + tramadol (Werneke Pharmacopsychiatry 2016 — single most-reported trigger combination); SSRI + linezolid (FDA 2011 boxed warning); SSRI + MAOI (phenelzine / selegiline); SSRI + triptan (FDA 2006 boxed warning); SSRI + methylene blue intraoperative (FDA 2011); SSRI + DXM / MDMA / cocaine / St John's wort / 5-HTP / lithium augmentation
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereavoid_succinylcholine_rhabdomyolysis
    Severe SS requiring intubation + paralysis — use rocuronium (non-depolarising); AVOID succinylcholine (depolarising) due to precipitation of hyperkalaemia from rhabdomyolysis (Boyer NEJM 2005 PMID 15784664)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereavoid_bromocriptine_in_serotonin
    Active serotonin syndrome — AVOID bromocriptine; the agent is pro-serotonergic (D2 agonist + indirect 5-HT release) and WORSENS serotonin syndrome; reserved for NMS rescue (the key NMS-vs-SS pharmacological pivot per Boyer NEJM 2005 PMID 15784664)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverelinezolid_with_ssri_combination
    Patient on SSRI / SNRI requiring linezolid (gram-positive antibiotic) — Linezolid is a reversible MAOI per FDA 2011 boxed warning; SS risk; alternative antibiotic preferred (vancomycin, daptomycin, ceftaroline) OR 2-week SSRI washout (5-week for fluoxetine due to norfluoxetine metabolite) before linezolid initiation
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatedepression_with_history_of_serotonin_syndrome
    Patient with prior SS episode requiring ongoing antidepressant management — review meds + chart-flag + alternative regimen counselling + slow titration if re-initiation needed (Boyer NEJM 2005; APA MDD 2023)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderaterecurrence_after_re_initiation
    Patient with prior SS episode developing recurrent features after re-initiation of any serotonergic agent — STOP + ED for acute management; clear chart-flag awareness gap + slow titration + alternative agent if possible going forward (Boyer NEJM 2005)
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Serotonin syndrome treatment ladder — STOP serotonergic + benzo + IV fluids + cooling → cyproheptadine for moderate-severe → ICU + intubation + paralysis (rocuronium) for severe; AVOID bromocriptine + succinylcholine + droperidol (Boyer NEJM 2005 PMID 15784664; Gillman Pharmacother 2010 PMID 20429837)
axis: serotonin_syndrome_treatment_ladderstep 1 - Step 1 — STOP all serotonergic agents + benzodiazepine IV + IV crystalloid + cooling (Boyer NEJM 2005 PMID 15784664 mandatory first step)
Selected step "Step 1 — STOP all serotonergic agents + benzodiazepine IV + IV crystalloid + cooling (Boyer NEJM 2005 PMID 15784664 mandatory first step)" — Any patient with Hunter criteria positive + serotonergic exposure within 24-72 h (Dunkley QJM 2003 PMID 12925718)
  • STOP all serotonergic agents
    first line
    discontinuation_action
    discontinue immediately • NA • immediate
    triggers: serotonin_syndrome_diagnosis_hunter_positive
    Boyer NEJM 2005 PMID 15784664 — mandatory first step; resolution within 24-48 h in 70% (Mason Medicine Baltimore 2000); without discontinuation, syndrome persists
  • lorazepam
    first line
    benzodiazepine
    1-2 mg IV q 5-10 min PRN (max 8 mg in 1 h) • IV • PRN titrated to sedation + neuromuscular control (max: 8 mg in 1 h initial; infusion if persistent)
    triggers: serotonin_syndrome_with_agitation_or_HTN_or_clonus, sympatholysis_required
    Boyer NEJM 2005 first-line — benzodiazepine for sympatholysis + neuromuscular control + sedation; titrate to symptom control + sedation level; lorazepam preferred for predictable hepatic metabolism (no active metabolite)
    rxcui 6470
  • diazepam
    first line
    benzodiazepine
    5-10 mg IV q 5-10 min PRN • IV • PRN (max: 60 mg in 1 h)
    triggers: serotonin_syndrome_with_severe_clonus, persistent_autonomic_features
    Boyer NEJM 2005 — alternative to lorazepam; longer half-life advantageous for sustained neuromuscular control; active metabolite (desmethyldiazepam) prolongs effect
    rxcui 3322
  • IV crystalloid (NS or LR)
    first line
    fluid_resuscitation
    500-1000 mL bolus then maintenance 100-150 mL/h • IV • continuous
    triggers: rhabdomyolysis_prophylaxis, volume_depletion_from_diaphoresis
    Boyer NEJM 2005 — volume + rhabdo prophylaxis; UOP target > 1 mL/kg/h; isotonic crystalloid first-line (NS or LR)
  • passive + active cooling (cooling blankets, ice packs, evaporative)
    first line
    cooling_supportive
    NA — supportive • NA • continuous until T < 38.5°C
    triggers: temperature_above_38.5C, severe_hyperthermia_above_41C_requires_aggressive_cooling_plus_paralysis
    Boyer NEJM 2005 — temperature control foundational; passive cooling (remove blankets, fans) for T > 38.5°C; aggressive cooling (ice packs, evaporative, surface cooling) + intubation + paralysis (rocuronium) for T > 41°C; mortality correlates with peak temperature

outpatient playbook — drug actions (5)

  1. 1. IF antidepressant required → bupropion 150-300 mg/day (NDRI) preferred; mirtazapine acceptable; AVOID re-initiation of trigger SSRI without 14-d MAOI washout (5-wk fluoxetine washout)
    rxcui 42347
    150 mg PO daily XL; titrate to 300 mg/day • PO • once daily
    trigger: Patient with depression history + SS recurrence prevention (APA MDD 2023)
    APA MDD 2023 — bupropion is NDRI with no serotonergic activity; SS-safe; activating; CONTRAINDICATED in seizure / eating disorder
  2. 2. IF migraine prophylaxis required → gepant (rimegepant 75 mg PO ODT PRN OR ubrogepant 50-100 mg PO PRN) preferred; AVOID triptans in SSRI-on-board (FDA 2006 boxed warning)
    rxcui 2282307
    rimegepant 75 mg PO ODT PRN; max 75 mg/day • PO ODT • PRN migraine
    trigger: Patient with migraine on SSRI requiring acute treatment (FDA 2006)
    CGRP antagonist no serotonergic activity; SS-safe alternative to triptan
  3. 3. IF analgesia required → acetaminophen + NSAID + non-tramadol opioid (oxycodone, morphine) preferred; AVOID tramadol in SS history
    rxcui 161
    acetaminophen 650-1000 mg PO q 6 h PRN; max 4 g/day • PO • q 6 h PRN
    trigger: Patient with chronic pain on tramadol pre-SS (Werneke 2016)
    Non-serotonergic analgesic options; tramadol is most-reported SS trigger in modern series
  4. 4. IF antibiotic with gram-positive cover required → AVOID linezolid in SSRI / SNRI patient (FDA 2011); alternative: vancomycin, daptomycin, ceftaroline
    per organism + clinical context • IV / PO • per regimen
    trigger: Patient on SSRI/SNRI needing gram-positive antibiotic (FDA 2011)
    Linezolid is reversible MAOI per FDA 2011 boxed warning; alternative gram-positive coverage
  5. 5. IF surgery requires methylene blue → reschedule surgery to allow SSRI washout (14 d; 5 wk fluoxetine); alternative: indocyanine green for perfusion mapping; AVOID methylene blue + SSRI intraoperatively (FDA 2011)
    NA — surgical planning • NA • pre-operative
    trigger: Patient on SSRI/SNRI scheduled for parathyroidectomy / NIRS perfusion mapping (FDA 2011)
    Methylene blue is potent MAOI per FDA 2011 surgical warning; SS risk if SSRI on board

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: Serotonergic agent (SSRI / SNRI / MAOI / linezolid / methylene blue / tramadol / triptan / fentanyl / DXM / MDMA / St John's wort / 5-HTP / lithium augmentation) initiated, dose-escalated, or added to existing regimen within 24-72 h (Boyer NEJM 2005 PMID 15784664); Triad of autonomic instability (tachycardia + diaphoresis + mydriasis + hyperthermia) + neuromuscular hyperactivity (clonus + hyperreflexia + tremor — lower-extremity dominant) + altered mental status (agitation / confusion) (Boyer NEJM 2005); Spontaneous clonus OR inducible clonus + agitation / diaphoresis (Hunter criteria; Dunkley QJM 2003 PMID 12925718).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Serotonin syndrome — toxidrome from serotonergic exposure (Hunter 2003 PMID 12925718; Boyer NEJM 2005 PMID 15784664); STOP serotonergic + benzo + cyproheptadine + cooling; severe → ICU + intubation + paralysis (rocuronium); AVOID bromocriptine + succinylcholine** (psych.serotonin-syndrome.v1).
Phenotype framing: SS vs NMS (AP exposure + lead-pipe rigidity + hyporeflexia + stupor + ↑↑ CK + days-weeks onset) vs anticholinergic toxidrome (mydriasis + dry skin + urinary retention + delirium WITHOUT clonus) vs sympathomimetic (MDMA / cocaine / methamphetamine — mydriasis + tachy + HTN + agitation WITHOUT clonus dominant) vs malignant hyperthermia (volatile anaesthetic exposure + masseter rigidity + ↑↑↑ CK + ↑↑↑ EtCO2) vs sepsis-driven encephalopathy (procalcitonin + culture + lactate) vs heat stroke (environmental + exertional history) vs thyroid storm (panel.thyroid TSH suppressed + Burch-Wartofsky) (Boyer NEJM 2005; Iqbal 2012)
Scope: Serotonin syndrome = drug-induced toxidrome from excess 5-HT2A agonism via serotonergic monotherapy or polypharmacy (SSRI/SNRI/MAOI/linezolid/methylene blue/tramadol/triptan/fentanyl/DXM/MDMA/St John's wort/5-HTP/lithium augmentation). Triad = autonomic instability + neuromuscular hyperactivity (clonus dominant) + AMS. Diagnosis via Hunter Serotonin Toxicity Criteria 2003 (sens 84% spec 97%) preferred over Sternbach 1991. Pharmacology pivot: STOP all serotonergic agents IMMEDIATELY; BENZODIAZEPINE FIRST for sympatholysis + neuromuscular control + sedation; cyproheptadine (5-HT2A antagonist) for moderate-severe disease; cooling for hyperthermia; AVOID bromocriptine (pro-serotonergic, reserved for NMS), succinylcholine (rhabdo hyperK), droperidol / haloperidol (QTc + dopaminergic worsening), routine dantrolene (limited SS evidence) (Boyer NEJM 2005 PMID 15784664).

No severity triggers fired against current inputs.

Plan

Regimen axis: **Serotonin syndrome treatment ladder — STOP serotonergic + benzo + IV fluids + cooling → cyproheptadine for moderate-severe → ICU + intubation + paralysis (rocuronium) for severe; AVOID bromocriptine + succinylcholine + droperidol (Boyer NEJM 2005 PMID 15784664; Gillman Pharmacother 2010 PMID 20429837)** — step "Step 1 — STOP all serotonergic agents + benzodiazepine IV + IV crystalloid + cooling (Boyer NEJM 2005 PMID 15784664 mandatory first step)".
1. STOP all serotonergic agents discontinue immediately NA immediate (discontinuation_action, first line) — Boyer NEJM 2005 PMID 15784664 — mandatory first step; resolution within 24-48 h in 70% (Mason Medicine Baltimore 2000); without discontinuation, syndrome persists
2. lorazepam 1-2 mg IV q 5-10 min PRN (max 8 mg in 1 h) IV PRN titrated to sedation + neuromuscular control (benzodiazepine, first line) — Boyer NEJM 2005 first-line — benzodiazepine for sympatholysis + neuromuscular control + sedation; titrate to symptom control + sedation level; lorazepam preferred for predictable hepatic metabolism (no active metabolite)
3. diazepam 5-10 mg IV q 5-10 min PRN IV PRN (benzodiazepine, first line) — Boyer NEJM 2005 — alternative to lorazepam; longer half-life advantageous for sustained neuromuscular control; active metabolite (desmethyldiazepam) prolongs effect
4. IV crystalloid (NS or LR) 500-1000 mL bolus then maintenance 100-150 mL/h IV continuous (fluid_resuscitation, first line) — Boyer NEJM 2005 — volume + rhabdo prophylaxis; UOP target > 1 mL/kg/h; isotonic crystalloid first-line (NS or LR)
5. passive + active cooling (cooling blankets, ice packs, evaporative) NA — supportive NA continuous until T < 38.5°C (cooling_supportive, first line) — Boyer NEJM 2005 — temperature control foundational; passive cooling (remove blankets, fans) for T > 38.5°C; aggressive cooling (ice packs, evaporative, surface cooling) + intubation + paralysis (rocuronium) for T > 41°C; mortality correlates with peak temperature

Setting playbook (outpatient) — Prevent recurrence — chart-flag in EHR allergy/ADR list, medication review at every visit, alternative regimen counselling, slow titration if re-initiation needed, patient + caregiver education on SS recognition + 24-h ED return precaution (Boyer NEJM 2005; APA MDD 2023)
6. IF antidepressant required → bupropion 150-300 mg/day (NDRI) preferred; mirtazapine acceptable; AVOID re-initiation of trigger SSRI without 14-d MAOI washout (5-wk fluoxetine washout) 150 mg PO daily XL; titrate to 300 mg/day PO once daily — Patient with depression history + SS recurrence prevention (APA MDD 2023) (APA MDD 2023 — bupropion is NDRI with no serotonergic activity; SS-safe; activating; CONTRAINDICATED in seizure / eating disorder)
7. IF migraine prophylaxis required → gepant (rimegepant 75 mg PO ODT PRN OR ubrogepant 50-100 mg PO PRN) preferred; AVOID triptans in SSRI-on-board (FDA 2006 boxed warning) rimegepant 75 mg PO ODT PRN; max 75 mg/day PO ODT PRN migraine — Patient with migraine on SSRI requiring acute treatment (FDA 2006) (CGRP antagonist no serotonergic activity; SS-safe alternative to triptan)
8. IF analgesia required → acetaminophen + NSAID + non-tramadol opioid (oxycodone, morphine) preferred; AVOID tramadol in SS history acetaminophen 650-1000 mg PO q 6 h PRN; max 4 g/day PO q 6 h PRN — Patient with chronic pain on tramadol pre-SS (Werneke 2016) (Non-serotonergic analgesic options; tramadol is most-reported SS trigger in modern series)
9. IF antibiotic with gram-positive cover required → AVOID linezolid in SSRI / SNRI patient (FDA 2011); alternative: vancomycin, daptomycin, ceftaroline per organism + clinical context IV / PO per regimen — Patient on SSRI/SNRI needing gram-positive antibiotic (FDA 2011) (Linezolid is reversible MAOI per FDA 2011 boxed warning; alternative gram-positive coverage)
10. IF surgery requires methylene blue → reschedule surgery to allow SSRI washout (14 d; 5 wk fluoxetine); alternative: indocyanine green for perfusion mapping; AVOID methylene blue + SSRI intraoperatively (FDA 2011) NA — surgical planning NA pre-operative — Patient on SSRI/SNRI scheduled for parathyroidectomy / NIRS perfusion mapping (FDA 2011) (Methylene blue is potent MAOI per FDA 2011 surgical warning; SS risk if SSRI on board)

Non-pharmacologic actions:
- Chart-flag in EHR — SS in allergy/ADR list permanent at every visit (Boyer NEJM 2005)
- Patient + caregiver education on SS recognition (tremor, clonus, agitation, hyperthermia, autonomic) + 24-h ED return precaution (Boyer NEJM 2005)
- Medication review at every visit — verify no inadvertent re-initiation of trigger drug or new serotonergic combination (Boyer NEJM 2005)
- Alternative regimen counselling for any prescription change involving serotonergic agent (Boyer NEJM 2005)
- Pharmacist MTM annually for SS-prevention review (Boyer NEJM 2005)
- Pain medicine consult if chronic pain requires non-tramadol regimen (Werneke 2016)
- Psychiatry consult if depression / SI requires continued SSRI / SNRI — slow titration if re-initiation; alternative agent preferred (APA MDD 2023)
- Family / caregiver re-education annually on SS recognition (Boyer NEJM 2005)
- Verify washout periods on all new prescriptions: 14 d MAOI; 5 wk fluoxetine (FDA; Boyer NEJM 2005)

AVOID / contraindication checks:
- AVOID_bromocriptine_in_serotonin_syndrome (Boyer NEJM 2005 PMID 15784664) — pro serotonergic, reserved for NMS; the key NMS vs SS pivot
- AVOID_succinylcholine_in_severe_SS_with_rhabdomyolysis (Boyer NEJM 2005) — use rocuronium
- AVOID_droperidol_haloperidol_for_SS_agitation (Boyer NEJM 2005) — QTc + dopaminergic worsening; benzo first line
- AVOID_routine_dantrolene_in_SS (Boyer NEJM 2005) — limited evidence; reserved for malignant hyperthermia / NMS
- STOP_all_serotonergic_agents_mandatory_first_step (Boyer NEJM 2005)
- MAOI_washout_14_days_before_re_initiation_5_weeks_for_fluoxetine (FDA; Boyer NEJM 2005)
- Linezolid_with_SSRI_high_SS_risk_alternative_antibiotic_or_2_week_SSRI_washout (FDA 2011 boxed warning; Iqbal Ochsner J 2012)
- Methylene_blue_with_SSRI_intraoperative_reschedule_surgery (FDA 2011 boxed warning)
- SSRI_with_triptan_FDA_2006_boxed_warning_consider_gepant_alternative (FDA 2006)
- SSRI_with_tramadol_high_SS_risk_alternative_analgesic_preferred (Werneke Pharmacopsychiatry 2016)
- Cyproheptadine_PO_NG_only_no_IV_formulation_crush_and_NG_if_intubated (Gillman Pharmacother 2010)
- Rocuronium_preferred_paralytic_in_severe_SS_avoid_succinylcholine (Boyer NEJM 2005)
- Chart_flag_in_EHR_allergy_ADR_list_after_SS_episode_for_recurrence_prevention (Boyer NEJM 2005)

Monitoring

Regimen monitoring:
- Hunter criteria re rate q 1 2h until resolution (Dunkley QJM 2003)
- Temperature q 15 30 min until T below 38C (Boyer NEJM 2005)
- Vital signs HR BP RR SpO2 q 15 30 min until stable (Boyer NEJM 2005)
- CK q 6h until trending down (rhabdo monitoring)
- Cr BMP q 6 12h until AKI excluded or resolving (rhabdo-AKI monitoring)
- UOP target above 1 mL per kg per h if rhabdo (Boyer NEJM 2005)
- Mental status q 1 2h until AMS resolved (Boyer NEJM 2005)
- ECG QTc baseline then q 24h during treatment (Boyer NEJM 2005)
- Sedation level continuous if benzo infusion (Boyer NEJM 2005)
- Respiratory rate SpO2 continuous if benzo infusion or intubated (Boyer NEJM 2005)
- Cyproheptadine effect at 2h post load then q 2h during titration (Gillman 2010)
- C SSRS at every clinical encounter in patient with underlying depression on SSRI (Posner 2011)
- Chart flag in EHR allergy ADR list at discharge to prevent recurrence (Boyer NEJM 2005)

Setting (outpatient) monitoring:
- Medication adherence + side effects at every visit (APA MDD 2023)
- PHQ-9 + GAD-7 q 1-3 months if longitudinal psych care (Kroenke 2001; Spitzer 2006)
- C-SSRS at every visit if SSRI / SNRI continued (Posner 2011)
- Drug interaction screen at every new prescription (Boyer NEJM 2005)
- Chart-flag review at every visit (Boyer NEJM 2005)

Follow-up plan: Comprehensive medication review at discharge + alternative regimens (e.g., switch tramadol to non-serotonergic analgesic — paracetamol / NSAID / non-tramadol opioid; switch SSRI to bupropion if depression amenable to NDRI; switch sumatriptan to gepant — rimegepant / ubrogepant — for migraine; switch linezolid to alternative gram-positive coverage if SSRI required); psychiatry consult if depression / SI driver; pharmacy MTM for SS-prevention education; document SS in EHR allergy/ADR list + chart-flag; pain medicine consult if chronic pain driving tramadol use; if MAOI was on board, mandatory 14-d washout before reintroducing serotonergic agent (5-wk for fluoxetine due to norfluoxetine metabolite); outpatient PCP / psychiatry follow-up at 1 week + 1 month; patient + caregiver education on SS recognition + 24-h ED return precaution (Boyer NEJM 2005; APA MDD 2023)
- Close-out criterion: Medication regimen revised + ADR documented + chart-flag in EHR + follow-up booked + patient/caregiver education completed (Boyer NEJM 2005)

Monitoring phase: Continuous ECG + telemetry; q 15-30 min BP + temp until stable; serial neuromuscular exam q 2-4 h (clonus + hyperreflexia resolution); CK q 6 h if rhabdo; UOP target > 1 mL/kg/h if rhabdo; mental status reassessment q 1 h initially; cyproheptadine effect at 2 h post-load; sedation level + airway protection assessment q 2 h if intubated. Resolution criteria: T < 38°C + clonus resolved + autonomic features resolved + AMS resolved (Boyer NEJM 2005)

Disposition

Current setting: outpatient — Prevent recurrence — chart-flag in EHR allergy/ADR list, medication review at every visit, alternative regimen counselling, slow titration if re-initiation needed, patient + caregiver education on SS recognition + 24-h ED return precaution (Boyer NEJM 2005; APA MDD 2023)

Disposition criteria:
- Continue outpatient indefinitely with chart-flag in EHR + annual SS-prevention review + pharmacist MTM (Boyer NEJM 2005)
- Step to community PCP if stable + on non-serotonergic regimen + no psych comorbidity needing specialty (APA MDD 2023)
- Refer to psychiatry if depression / anxiety requires SSRI / SNRI re-initiation with slow titration + close monitoring (APA MDD 2023)
- Refer to pain medicine if chronic pain requires non-tramadol opioid regimen (Werneke 2016)

Escalation triggers (move to higher acuity):
- Recurrence of SS features (tremor, clonus, autonomic, AMS) after re-initiation of any serotonergic agent → STOP + ED for acute management (Boyer NEJM 2005; severity_trigger:recurrence_after_re_initiation)
- Active SI on C-SSRS → ED + possible psych admission (Posner 2011; route to psych.suicidality.ed.core.v1)
- Worsening depression on bupropion / alternative regimen → reconsider SSRI re-initiation with slow titration + close monitoring + chart-flag awareness (APA MDD 2023)
- New SSRI / SNRI / MAOI / linezolid / tramadol / triptan prescription identified at pharmacy or specialty clinic → review with patient + alternative consideration (Boyer NEJM 2005)

Patient Action Plan

**Serotonin syndrome action plan — recurrence prevention + early warning signs (Boyer NEJM 2005; APA MDD 2023)**
Personalised values: prior_serotonin_syndrome_episode_features, current_antidepressant_regimen, current_analgesic_regimen, identified_supports, crisis_line_numbers, allergy_ADR_chart_flag_status, pharmacist_contact, PCP_psychiatrist_contact.

**Doing well — on non-serotonergic alternative regimen OR on SSRI with no symptoms; chart-flag in EHR active (Boyer NEJM 2005)** (green):
Triggers:
- No tremor, clonus, agitation, hyperthermia (Boyer NEJM 2005)
- No new serotonergic agent prescribed at any visit (Boyer NEJM 2005)
- Chart-flag in EHR active and reviewed at every visit (Boyer NEJM 2005)
- Stable mood + sleep + energy on alternative regimen (APA MDD 2023)
- Patient + caregiver know SS warning signs (Boyer NEJM 2005)
Actions:
- Take antidepressant / analgesic / migraine medication as prescribed (APA MDD 2023)
- Verify SS chart-flag at every clinical visit (Boyer NEJM 2005)
- Show your current med list to every new provider + pharmacist (Boyer NEJM 2005)
- Avoid new OTC cold medications, supplements (St John's wort, 5-HTP) without checking with pharmacist (Boyer NEJM 2005)
- Keep crisis line numbers available (988 US) (APA MDD 2023)

**Caution — new prescription started OR mild tremor / restlessness / sweating (Boyer NEJM 2005)** (yellow):
Triggers:
- New SSRI / SNRI / tramadol / triptan / linezolid / DXM prescription (Boyer NEJM 2005)
- Mild tremor or jitteriness (Boyer NEJM 2005)
- Mild diaphoresis or feeling warm without fever (Boyer NEJM 2005)
- Mild restlessness or agitation (Boyer NEJM 2005)
- Started new herbal supplement (St John's wort, 5-HTP) (Boyer NEJM 2005)
- Used recreational MDMA / cocaine / DXM (Boyer NEJM 2005)
Actions:
- Call your prescriber or pharmacist within 24 h to review new medication (Boyer NEJM 2005)
- Do not start new herbal supplement without checking (Boyer NEJM 2005)
- Stop recreational drug use immediately (Boyer NEJM 2005)
- Take your temperature q 4 h while symptoms present (Boyer NEJM 2005)
- Use coping strategies + contact support person (APA MDD 2023)
Contact provider when:
- New symptom persists > 24 h (Boyer NEJM 2005)
- Temperature rises above 38°C (Boyer NEJM 2005)
- Tremor worsening or hyperreflexia developing (Boyer NEJM 2005)
- Agitation worsening (Boyer NEJM 2005)

**Medical alert — frank serotonin syndrome features (Boyer NEJM 2005)** (red):
Triggers:
- Temperature > 38°C with rigid muscles or clonus (Boyer NEJM 2005)
- Severe tremor or jerking movements (clonus) (Boyer NEJM 2005)
- Severe agitation, confusion, or seeing things (Boyer NEJM 2005)
- Rapid heart rate + sweating + high blood pressure (Boyer NEJM 2005)
- Diarrhoea + nausea + flushing in setting of serotonergic exposure (Boyer NEJM 2005)
- Difficulty staying awake or breathing (Boyer NEJM 2005)
Actions:
- Call 911 (US) / your local emergency services NOW (Boyer NEJM 2005)
- Go to the nearest emergency department — do not be alone (Boyer NEJM 2005)
- Tell the ED you have a history of serotonin syndrome — bring your med list (Boyer NEJM 2005)
- Tell someone you trust what is happening immediately (Boyer NEJM 2005)
- Do not take more of any medication (Boyer NEJM 2005)
- Do not use any substances (Boyer NEJM 2005)
Contact provider when:
- Any red zone trigger — emergency department immediately (Boyer NEJM 2005)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Severe SS with hyperthermia > 41°C + rigidity + rhabdomyolysis + multi-organ involvement OR refractory autonomic instability — life-threatening; ICU + intubation + paralysis (rocuronium, AVOID succinylcholine) + active cooling + benzo infusion + cyproheptadine NG (Boyer NEJM 2005 PMID 15784664)
- [LIFE_THREATENING] NMS (Neuroleptic Malignant Syndrome) converging differential — antipsychotic exposure within 1-2 weeks + lead-pipe rigidity (NOT clonus) + hyporeflexia + stupor / mutism (NOT agitation) + hyperthermia + autonomic instability + ↑↑ CK (often > 10× normal) + days-weeks onset (Strawn AJP 2007; Caroff + Mann 1993). Treatment DIFFERS critically — bromocriptine 2.5 mg PO/NG TID + dantrolene 1-2.5 mg/kg IV q 6 h for NMS, NOT for SS (bromocriptine is pro-serotonergic and WORSENS SS) — the key NMS-vs-SS pharmacological pivot
- [SEVERE] Moderate SS — T 38-40°C + clonus + agitation + persistent autonomic features after initial benzo; treatment: discontinue all offending agents + benzo IV + cyproheptadine 12 mg PO load → 2 mg PO q 2 h + monitor (Boyer NEJM 2005 PMID 15784664; Gillman Pharmacother 2010 PMID 20429837)

Citations

- Boyer + Shannon NEJM 2005 PMID 15784664 (canonical review + management algorithm) + Dunkley QJM 2003 PMID 12925718 (Hunter Serotonin Toxicity Criteria — sens 84% spec 97%) + Gillman Pharmacother 2010 PMID 20429837 (cyproheptadine mechanism + evidence base) + FDA 2011 linezolid + methylene blue boxed warnings + FDA 2006 SSRI + triptan boxed warning + APA MDD 2023 [PMID:15784664](https://pubmed.ncbi.nlm.nih.gov/15784664/)
- Cited evidence (PMID 12925718) [PMID:12925718](https://pubmed.ncbi.nlm.nih.gov/12925718/)
- Cited evidence (PMID 20429837) [PMID:20429837](https://pubmed.ncbi.nlm.nih.gov/20429837/)
- Cited evidence (PMID 23230406) [PMID:23230406](https://pubmed.ncbi.nlm.nih.gov/23230406/)

Last reconciled with current guidelines: 2026-05-15.
References
  • Boyer + Shannon NEJM 2005 PMID 15784664 (canonical review + management algorithm) + Dunkley QJM 2003 PMID 12925718 (Hunter Serotonin Toxicity Criteria — sens 84% spec 97%) + Gillman Pharmacother 2010 PMID 20429837 (cyproheptadine mechanism + evidence base) + FDA 2011 linezolid + methylene blue boxed warnings + FDA 2006 SSRI + triptan boxed warning + APA MDD 2023 — PMID:15784664
  • Cited evidence (PMID 12925718) — PMID:12925718
  • Cited evidence (PMID 20429837) — PMID:20429837
  • Cited evidence (PMID 23230406) — PMID:23230406