Serotonin syndrome: Difference between revisions

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==Background==
==Background==
*Can be produced by any serotonergic medication
*Drug-induced excess serotonergic activity in CNS and peripheral nervous system
*1 in 6 U.S. adults take at least one psychoactive medication<ref>Moore TJ and Mattison DR. Adult Utilization of Psychiatric Drugs and Differences by Sex, Age, and Race. JAMA Intern Med. Published online December 12, 2016. doi:10.1001/jamainternmed.2016.7507.</ref>
*Usually results from combination of serotonergic agents or dose increase of a single agent
*Majority of cases occur within therapeutic drug dosages
*Onset typically within 6-24 hours (usually within 6 hours of medication change)
*Most common cause is ingestion of foods high in L-Tryptophan while taking an MAOI. Second most common is ingestion of both SSRI and MAOI<ref>Stork CM. Serotonin Reuptake Inhibitors and Atypical Antidepressants. In: Flomenbaum N, Goldfrank L, Hoffman R, Howland MA, et al, eds. Goldfrank’s Toxicologic Emergencies. 8th Ed. New York, NY: McGraw-Hill; 2006: 1070-1082</ref>
*Mild cases are common; '''severe cases can be life-threatening'''
*Most common cause of death is severe hyperthermia
*Mortality ~2-12% in severe cases


===Causative Agents<ref>Brown CH. Drug-induced Serotonin Syndrome. US Pharm. 2010;35(11):HS-16-HS-21.</ref>===
===Common Causative Agents===
====Antidepressants====
*SSRIs: fluoxetine, sertraline, paroxetine, citalopram, escitalopram
*[[SSRIs]]
*SNRIs: venlafaxine, duloxetine
*[[SNRIs]]
*MAOIs: phenelzine, tranylcypromine, selegiline, linezolid, methylene blue
*[[Bupropion]]<ref>Thorpe EL, Pizon AF, Lynch MJ, Boyer J. Bupropion induced serotonin syndrome: a case report. J Med Toxicol. 2010;6(2):168-171. doi:10.1007/s13181-010-0021-x</ref>
*TCAs: amitriptyline, clomipramine
*[[Buspirone]]
*Opioids: tramadol, meperidine (Demerol), fentanyl, methadone
*[[TCAs]]
*Triptans: sumatriptan (controversial, risk likely low)
*[[Lithium]]
*Other: dextromethorphan, [[lithium]], MDMA ("ecstasy"), cocaine, ondansetron (rare)
*[[Mirtazapine]]
*Most dangerous combination: MAOI + serotonergic agent
*[[Trazodone]]
*[[Valproic acid]]
*MAOIs (should have washout period of 2+ weeks prior to starting a SSRI)
**Phenelzine
**Selegiline
**Tranylcypromine


====Drugs of Abuse====
==Clinical Features==
*[[Cocaine]]
*Rapid onset (hours) — distinguishes from [[neuroleptic malignant syndrome]] (days)
*[[Ecstasy (MDMA)]]
*Hunter Serotonin Toxicity Criteria<ref>Dunkley EJ, et al. The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules. ''QJM''. 2003;96(9):635-642. PMID 12925718</ref> (most sensitive/specific):
*[[Methamphetamine]]
**In setting of serotonergic agent + any ONE of:
*[[LSD]]
***Spontaneous clonus (most important finding)
***Inducible clonus + agitation or diaphoresis
***Ocular clonus + agitation or diaphoresis
***Tremor + hyperreflexia
***Hypertonia + temperature >38°C + ocular or inducible clonus


====Analgesics====
===Clinical Triad===
*[[Fentanyl]]
*Neuromuscular excitation: clonus (spontaneous, inducible, or ocular), hyperreflexia, tremor, myoclonus, rigidity (severe)
*[[Meperidine]] (Demerol)
*Autonomic dysfunction: diaphoresis, [[tachycardia]], [[hyperthermia]], hypertension, mydriasis, hyperactive bowel sounds, diarrhea
*[[Methadone]]
*'''Altered mental status''': agitation, anxiety, confusion, delirium
*[[Tramadol]]


====[[Antiemetics]]====
===Severity Spectrum===
*[[Metoclopramide]]
*Mild: tremor, hyperreflexia, tachycardia, diaphoresis
*[[Ondansetron]]
*Moderate: agitation, clonus, mydriasis, hyperthermia (≤40°C)
*Severe: hyperthermia >40°C, rigidity, seizures, [[rhabdomyolysis]], [[DIC]], cardiovascular collapse


====Over the counter Medications====
==Differential Diagnosis==
*[[Dextromethorphan]]
{| class="wikitable"
*Oral decongestants ([[Pseudoephedrine]])
|-
! Feature !! '''Serotonin Syndrome''' !! '''[[Neuroleptic malignant syndrome]]''' !! '''[[Anticholinergic toxicity]]''' !! '''[[Malignant hyperthermia]]'''
|-
| Onset || '''Hours''' || Days || Hours || Minutes (OR)
|-
| Key finding || '''Clonus/hyperreflexia''' || Lead-pipe rigidity || Mydriasis, dry || Generalized rigidity
|-
| Bowel sounds || '''Hyperactive''' || Normal/decreased || '''Absent''' || Normal
|-
| Skin || Diaphoresis || Diaphoresis || '''Dry, flushed''' || Mottled
|-
| Pupils || Mydriasis || Normal || Mydriasis || Normal
|-
| CK || Mildly elevated || >1000 || Normal || Markedly elevated
|}


====Herbal products====
==Evaluation==
*St John’s Wort, Ginseng, Nutmeg, Yohimbe
*Clinical diagnosis based on Hunter criteria — no confirmatory lab test
*CK: mildly elevated (markedly elevated if severe → [[rhabdomyolysis]])
*BMP: electrolytes, creatinine (renal injury), bicarbonate (acidosis)
*CBC, LFTs
*Lactate
*Coagulation studies (DIC in severe cases)
*Core temperature
*Medication reconciliation is essential — identify all serotonergic agents


====Other Medications====
==Management==
*Triptans
===Immediate===
*Ergot alkaloids
*Discontinue ALL serotonergic agents
*Bromocriptine
*Most mild cases resolve within 24-72 hours after drug cessation
*[[Linezolid]]
*[[Carbamazepine]]
*[[Cyclobenzaprine]]
*L-tryptophan, 5-hydroxytryptophan
*[[Methylene blue]]


==Clinical Features==
===Mild (Tremor, Hyperreflexia)===
*[[Altered mental status]]: Agitated delirium.  Patients generally hyperactive.
*Observation, IV fluids, benzodiazepines PRN for agitation
*Autonomic Instability: Hyperthermia, tachycardia, hypertension, diaphoresis, gastrointestinal illness <ref>Boyer, E. W. and Shannon, M. (2005) ‘The Serotonin Syndrome’, New England Journal of Medicine, 352(11), pp. 1112–1120. doi: 10.1056/nejmra041867</ref>
*Supportive care
**Often labile blood pressure, HR
*Neuromuscular Abnormalities: Clonus, ocular clonus, myoclonus, rigidity, hyperreflexia, tremor, seizures
**More pronounced in the lower extremities
**Clonus (inducible or spontaneous): most common finding<ref>Farkas, J. Serotonin Syndrome. The Internet Book of Critical Care. https://emcrit.org/ibcc/serotonin/. Published June 13th, 2019. Accessed December 31st, 2020.</ref>
***Important to identify because it does not occur in other conditions that mimic serotonin syndrome
**Hyperactivity as opposed to rigidity in [[neuroleptic malignant syndrome]]


==Differential Diagnosis==
===Moderate (Agitation, Clonus, Hyperthermia <40°C)===
{{Movement disorder DDX}}
*Benzodiazepines for agitation and autonomic instability:
{{AMS and fever DDX}}
**Lorazepam 2-4 mg IV q5-10min, or midazolam
*Active cooling for hyperthermia (evaporative cooling, ice packs)
*IV fluid resuscitation


==Evaluation==
===Severe (Hyperthermia >40°C, Rigidity, Seizures)===
===Hunter Toxicity Criteria Decision Rules===
*Cyproheptadine (serotonin antagonist):
Serotonergic agent plus 1 of the following<ref>Dunkley EJ, Isbister GK, Sibbritt D, Dawson AH, Whyte IM. The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules for serotonin toxicity. QJM 2003;96:635-642</ref>:
**12 mg PO/NG initial dose, then 2 mg q2h until clinical improvement
*Spontaneous clonus
**Maintenance: 8 mg PO q6h
*Inducible clonus AND (agitation or diaphoresis)
**Only available PO/NG — '''crush and give via NG if intubated'''
*Ocular Clonus AND (agitation or diaphoresis)
*'''Intubation with neuromuscular blockade''' for severe rigidity/hyperthermia
*Tremor AND hyperreflexia
**Use non-depolarizing agent (avoid succinylcholine if hyperkalemia/rhabdomyolysis risk)
*Hypertonia AND temperature >38 AND (ocular clonus or inducible clonus)
*Aggressive cooling
*Benzodiazepines for seizures


''84% Sn, 97% Sp''
===What to Avoid===
 
*NO antipyretics (not effective — hyperthermia is from muscle activity, not altered setpoint)
{{Serotonin syndrome vs neuroleptic malignant syndrome}}
*NO bromocriptine (for NMS, not SS)
 
*NO dantrolene (limited role; rigidity in SS is different from NMS)
==Management==
*Avoid restraints alone without chemical sedation (isometric muscle contraction worsens hyperthermia)
*Discontinue all serotonergic drugs
*Aggressive supportive care
**If pressors required, direct acting (e.g. norepinephrine, epi) preferred, MAO inhibition causes erratic response to dopamine
*[[Benzos]]
**Goal is to eliminate agitation, neuromuscular abnormalities, elevations in HR/BP
**In severe cases, large doses are required (diazepam IV 10-20 mg, titrated with 10 mg increments)
*[[Cyproheptadine]]<ref>Graudins, A., Stearman, A. and Chan, B. (1998) ‘Treatment of the serotonin syndrome with cyproheptadine’, The Journal of Emergency Medicine, 16(4), pp. 615–619. doi: 10.1016/s0736-4679(98)00057-2</ref>
**Give if benzodiazepines and supportive care fail to improve agitation and abnormal vitals
**Serotonin antagonist
***Also has antihistamine and anticholinergic properties that may exacerbate other mixed toxicology picture
**Give 12mg PO/NG; repeat with 2mg q2hr until clinical response is seen (max 32mg/d)
**Give 4mg q6hr x48hr if patient is responsive to initial dose
*[[Chlorpromazine]]<ref>Gillman PK. The serotonin syndrome and its treatment. J Psychopharmacol 1999;13:100-109</ref>
**Phenothiazine with antiserotonergic effects
**50mg to 100mg IM
**Avoid in:
***Hemodynamically unstable patients as can cause serious hypotension<ref>Frank C. Recognition and treatment of serotonin syndrome. Can Fam Physician. 2008 Jul; 54(7): 988–992.</ref>
***Cases in which NMS may still be on the differential
*[[Dexmedetomidine]]<ref>Rushton WF, Charlton NP. Dexmedetomidine in the treatment of serotonin syndrome. Ann Pharmacother. 2014; 48(12):1651-1654.</ref><ref>Duggal HS, Fetchko J. Serotonin syndrome and atypical antipsychotics. Am J Psychiatry. 2002;159(4):672–3.</ref>
**Small case series found this helpful in adolescent cases refractory to benzos
*Dantrolene generally not recommended as it can worsen serotonin toxicity<ref>Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005 Mar 17; 352(11):1112-20.</ref>
*Treat hyperthermia
**Hyperthermia due to increase in muscular activity, not change in set point
**[[Intubate]] and paralyze if temperature > 41.1
**Standard [[cooling measures]]
***Fans, water sprays, ice packs, cooled crystalloids, cooling blankets


==Disposition==
==Disposition==
*Severe cases may require [[intubation]] and [[ventilation]] in ICU
*Mild: observe 6-12 hours; discharge if improving after drug cessation
*24hr admission for [[altered mental status]] or abnormal [[vital signs]] requiring further supportive care
*Moderate: admit to monitored bed
*Discharge mild cases with minimal intervention required after 6 hrs of observation
*Severe: ICU admission
 
*Symptoms typically resolve within 24-72 hours (longer for fluoxetine/MAOIs — longer half-life)
*Before restarting serotonergic medications: allow washout period (5 half-lives)
**Fluoxetine: 5 weeks; MAOIs: 2 weeks


<div style="display:none">
<!-- SMW MedicationDose annotations for serotonin syndrome medications -->
{{MedicationDose|drug=Diazepam|dose=10-20 mg IV, titrate with 10 mg increments|route=IV|context=Benzodiazepine for agitation/neuromuscular abnormalities|indication=Serotonin syndrome|notes=Goal: eliminate agitation, neuromuscular abnormalities, HR/BP elevations}}
{{MedicationDose|drug=Cyproheptadine|dose=12 mg PO/NG initial, then 2 mg q2h until response (max 32 mg/day); then 4 mg q6h x48h|route=PO/NG|context=Serotonin antagonist (if benzos and supportive care fail)|indication=Serotonin syndrome|max_dose=32 mg/day|notes=Also has antihistamine and anticholinergic properties}}
</div>
==See Also==
==See Also==
*[[Toxidromes]]
*[[Neuroleptic malignant syndrome]]
*[[Anticholinergic toxicity]]
*[[Malignant hyperthermia]]
*[[Toxicology]]
*[[MAOI toxicity]]


==References==
==References==
<references/>
<references/>
*Boyer EW, Shannon M. The serotonin syndrome. ''N Engl J Med''. 2005;352(11):1112-1120. PMID 15784664
*Isbister GK, et al. Serotonin toxicity: a practical approach to diagnosis and treatment. ''Med J Aust''. 2007;187(6):361-365. PMID 17874986
*Ables AZ, Nagubilli R. Prevention, recognition, and management of serotonin syndrome. ''Am Fam Physician''. 2010;81(9):1139-1142. PMID 20433130


[[Category:Toxicology]]
[[Category:Toxicology]]
[[Category:Psychiatry]]

Latest revision as of 09:30, 22 March 2026

Background

  • Drug-induced excess serotonergic activity in CNS and peripheral nervous system
  • Usually results from combination of serotonergic agents or dose increase of a single agent
  • Onset typically within 6-24 hours (usually within 6 hours of medication change)
  • Mild cases are common; severe cases can be life-threatening
  • Mortality ~2-12% in severe cases

Common Causative Agents

  • SSRIs: fluoxetine, sertraline, paroxetine, citalopram, escitalopram
  • SNRIs: venlafaxine, duloxetine
  • MAOIs: phenelzine, tranylcypromine, selegiline, linezolid, methylene blue
  • TCAs: amitriptyline, clomipramine
  • Opioids: tramadol, meperidine (Demerol), fentanyl, methadone
  • Triptans: sumatriptan (controversial, risk likely low)
  • Other: dextromethorphan, lithium, MDMA ("ecstasy"), cocaine, ondansetron (rare)
  • Most dangerous combination: MAOI + serotonergic agent

Clinical Features

  • Rapid onset (hours) — distinguishes from neuroleptic malignant syndrome (days)
  • Hunter Serotonin Toxicity Criteria[1] (most sensitive/specific):
    • In setting of serotonergic agent + any ONE of:
      • Spontaneous clonus (most important finding)
      • Inducible clonus + agitation or diaphoresis
      • Ocular clonus + agitation or diaphoresis
      • Tremor + hyperreflexia
      • Hypertonia + temperature >38°C + ocular or inducible clonus

Clinical Triad

  • Neuromuscular excitation: clonus (spontaneous, inducible, or ocular), hyperreflexia, tremor, myoclonus, rigidity (severe)
  • Autonomic dysfunction: diaphoresis, tachycardia, hyperthermia, hypertension, mydriasis, hyperactive bowel sounds, diarrhea
  • Altered mental status: agitation, anxiety, confusion, delirium

Severity Spectrum

  • Mild: tremor, hyperreflexia, tachycardia, diaphoresis
  • Moderate: agitation, clonus, mydriasis, hyperthermia (≤40°C)
  • Severe: hyperthermia >40°C, rigidity, seizures, rhabdomyolysis, DIC, cardiovascular collapse

Differential Diagnosis

Feature Serotonin Syndrome Neuroleptic malignant syndrome Anticholinergic toxicity Malignant hyperthermia
Onset Hours Days Hours Minutes (OR)
Key finding Clonus/hyperreflexia Lead-pipe rigidity Mydriasis, dry Generalized rigidity
Bowel sounds Hyperactive Normal/decreased Absent Normal
Skin Diaphoresis Diaphoresis Dry, flushed Mottled
Pupils Mydriasis Normal Mydriasis Normal
CK Mildly elevated >1000 Normal Markedly elevated

Evaluation

  • Clinical diagnosis based on Hunter criteria — no confirmatory lab test
  • CK: mildly elevated (markedly elevated if severe → rhabdomyolysis)
  • BMP: electrolytes, creatinine (renal injury), bicarbonate (acidosis)
  • CBC, LFTs
  • Lactate
  • Coagulation studies (DIC in severe cases)
  • Core temperature
  • Medication reconciliation is essential — identify all serotonergic agents

Management

Immediate

  • Discontinue ALL serotonergic agents
  • Most mild cases resolve within 24-72 hours after drug cessation

Mild (Tremor, Hyperreflexia)

  • Observation, IV fluids, benzodiazepines PRN for agitation
  • Supportive care

Moderate (Agitation, Clonus, Hyperthermia <40°C)

  • Benzodiazepines for agitation and autonomic instability:
    • Lorazepam 2-4 mg IV q5-10min, or midazolam
  • Active cooling for hyperthermia (evaporative cooling, ice packs)
  • IV fluid resuscitation

Severe (Hyperthermia >40°C, Rigidity, Seizures)

  • Cyproheptadine (serotonin antagonist):
    • 12 mg PO/NG initial dose, then 2 mg q2h until clinical improvement
    • Maintenance: 8 mg PO q6h
    • Only available PO/NG — crush and give via NG if intubated
  • Intubation with neuromuscular blockade for severe rigidity/hyperthermia
    • Use non-depolarizing agent (avoid succinylcholine if hyperkalemia/rhabdomyolysis risk)
  • Aggressive cooling
  • Benzodiazepines for seizures

What to Avoid

  • NO antipyretics (not effective — hyperthermia is from muscle activity, not altered setpoint)
  • NO bromocriptine (for NMS, not SS)
  • NO dantrolene (limited role; rigidity in SS is different from NMS)
  • Avoid restraints alone without chemical sedation (isometric muscle contraction worsens hyperthermia)

Disposition

  • Mild: observe 6-12 hours; discharge if improving after drug cessation
  • Moderate: admit to monitored bed
  • Severe: ICU admission
  • Symptoms typically resolve within 24-72 hours (longer for fluoxetine/MAOIs — longer half-life)
  • Before restarting serotonergic medications: allow washout period (5 half-lives)
    • Fluoxetine: 5 weeks; MAOIs: 2 weeks

See Also

References

  1. ↑ Dunkley EJ, et al. The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules. QJM. 2003;96(9):635-642. PMID 12925718
  • Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005;352(11):1112-1120. PMID 15784664
  • Isbister GK, et al. Serotonin toxicity: a practical approach to diagnosis and treatment. Med J Aust. 2007;187(6):361-365. PMID 17874986
  • Ables AZ, Nagubilli R. Prevention, recognition, and management of serotonin syndrome. Am Fam Physician. 2010;81(9):1139-1142. PMID 20433130
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