Pharmacology · Year 2 · from Pharmacology
Case 2: Serotonin Syndrome - Drug Interaction Toxicity
Patient Demographics
- Age: 34 years
- Sex: Male
- Occupation: Software developer
Chief Complaint
"He's shaking uncontrollably and sweating through his clothes."
History of Present Illness
A 34-year-old man is brought to the emergency department by his wife after she found him at home confused, trembling, and drenched in sweat. He has a history of depression treated with sertraline 100 mg daily for 2 years. Three days ago, he saw a new primary care physician for back pain and was prescribed tramadol 50 mg every 6 hours. Today, he also took St. John's Wort (herbal supplement) that he purchased to "help with his mood" as he had been feeling more depressed. Within hours of taking the St. John's Wort, he developed tremor, agitation, and profuse sweating. His wife notes his symptoms have been rapidly worsening over the past 2 hours.
Medications and Supplements
- Sertraline 100 mg daily (SSRI - selective serotonin reuptake inhibitor)
- Tramadol 50 mg q6h (opioid with serotonin reuptake inhibition, started 3 days ago)
- St. John's Wort (herbal - induces serotonin release, taken today)
Physical Examination
- Vital Signs: T 39.2C (102.6F), HR 128 bpm, BP 162/98 mmHg, RR 24/min
- General: Diaphoretic, agitated, restless, cannot lie still
- HEENT: Pupils 6 mm bilaterally, reactive; dry mucous membranes
- Neurologic:
- Mental status: Agitated, confused, disoriented
- Tremor: Generalized, coarse
- Clonus: Inducible clonus at ankles bilaterally (>3 beats)
- Hyperreflexia: 3+ reflexes throughout
- Muscle rigidity: Increased tone, more prominent in lower extremities
- Skin: Flushed, profusely diaphoretic
- Abdomen: Hyperactive bowel sounds
Diagnosis
Serotonin Syndrome
Hunter Criteria for Serotonin Syndrome: In the presence of a serotonergic agent, ONE of the following:
- Spontaneous clonus
- Inducible clonus + agitation or diaphoresis
- Ocular clonus + agitation or diaphoresis
- Tremor + hyperreflexia
- Hypertonia + temperature >38C + ocular or inducible clonus
This Patient Meets Criteria:
- Serotonergic agents: Sertraline + Tramadol + St. John's Wort (triple hit)
- Has: Inducible clonus + diaphoresis + agitation
- Also has: Tremor + hyperreflexia
- Also has: Temperature 39.2C + inducible clonus
Pathophysiology of Serotonin Syndrome
Serotonin (5-HT) Excess in CNS and Periphery:
Serotonergic Drug Mechanisms:
| Mechanism | Examples |
|---|---|
| Increase serotonin synthesis | L-tryptophan |
| Increase serotonin release | St. John's Wort, amphetamines, MDMA |
| Inhibit serotonin reuptake | SSRIs (sertraline), SNRIs, tramadol, TCAs, meperidine |
| Inhibit serotonin metabolism | MAOIs, linezolid |
| Direct serotonin receptor agonism | Triptans, buspirone, LSD |
This Patient's Triple Combination:
- Sertraline: Blocks serotonin reuptake (SERT inhibitor)
- Tramadol: Blocks serotonin reuptake (in addition to opioid effect)
- St. John's Wort: Multiple mechanisms - induces serotonin release, weak MAOI
Clinical Features by System:
| System | Manifestations | Mechanism |
|---|---|---|
| Neuromuscular | Clonus, hyperreflexia, tremor, rigidity | 5-HT1A receptor activation in spinal cord |
| Autonomic | Hyperthermia, diaphoresis, tachycardia, hypertension, mydriasis, diarrhea | Peripheral 5-HT effects + hypothalamic dysregulation |
| Mental Status | Agitation, confusion, anxiety | CNS serotonin excess |
Distinguishing Serotonin Syndrome from Neuroleptic Malignant Syndrome
| Feature | Serotonin Syndrome | NMS |
|---|---|---|
| Onset | Rapid (hours) | Gradual (days) |
| Causative agent | Serotonergic drugs | Dopamine antagonists (antipsychotics) |
| Neuromuscular | Clonus, hyperreflexia | "Lead-pipe" rigidity, bradyreflexia |
| Tremor | Yes (often) | Less common |
| Clonus | Characteristic | Absent |
| Pupils | Dilated | Normal |
| Bowel sounds | Hyperactive | Decreased |
| Lab findings | Mild CK elevation | Markedly elevated CK |
| Resolution | Rapid (24-72h) | Days to weeks |
Key Differentiator: Clonus and hyperreflexia point to serotonin syndrome; "lead-pipe" rigidity and bradyreflexia point to NMS
Treatment
1. DISCONTINUE ALL SEROTONERGIC AGENTS:
- Stop sertraline, tramadol, St. John's Wort immediately
- Review medication list for any other serotonergic drugs
2. SUPPORTIVE CARE (Mainstay of Treatment):
- IV fluids for volume depletion from diaphoresis
- External cooling for hyperthermia (cooling blankets, ice packs)
- Avoid antipyretics (hyperthermia is from muscle activity, not hypothalamic setpoint)
- Benzodiazepines for agitation and to reduce muscle hyperactivity:
- Lorazepam 2 mg IV, repeat as needed
- Also helps control autonomic instability
3. SEROTONIN ANTAGONIST (for moderate-severe cases):
- Cyproheptadine:
- First-generation antihistamine with 5-HT2A antagonist activity
- Loading dose: 12 mg PO/NG
- Maintenance: 2 mg every 2 hours until symptoms improve, then 8 mg every 6 hours
- Only available in oral form
- Reserve for cases not responding to benzodiazepines and supportive care
4. AVOID:
- Physical restraints (can worsen hyperthermia from muscle activity)
- Antipyretics (ineffective for muscular hyperthermia)
- Succinylcholine if intubation needed (hyperkalemia risk from muscle rigidity)
5. SEVERE CASES:
- Intubation with non-depolarizing paralytic for refractory hyperthermia
- ICU admission
Clinical Course
- Sertraline, tramadol, St. John's Wort discontinued
- IV fluids administered
- Lorazepam 2 mg IV x 3 doses with improvement in agitation
- Cooling blankets applied; temperature decreased to 37.8C within 4 hours
- Cyproheptadine 12 mg given via NG tube
- Significant improvement within 12 hours
- Clonus resolved by 24 hours
- Transferred out of ICU on day 2
- Discharged day 3 with psychiatry follow-up for depression management
Prevention and Patient Education
Key Drug Interactions to Avoid:
- SSRI/SNRI + tramadol
- SSRI/SNRI + MAOIs (contraindicated; requires 2-week washout)
- SSRI + St. John's Wort
- SSRI + triptans (use with caution)
- SSRI + linezolid (linezolid is a weak MAOI)
- SSRI + meperidine
- Multiple serotonergic agents concurrently
Patient Counseling:
- Inform ALL providers about antidepressant use
- Check with pharmacist before starting any new medication or supplement
- St. John's Wort has real pharmacologic activity and drug interactions
- Know warning signs: confusion, tremor, sweating, muscle twitching
- Seek immediate care if symptoms develop
Clinical Pearl
Serotonin syndrome is a potentially life-threatening drug-induced condition caused by excess serotonergic activity. The hallmark clinical findings are clonus (spontaneous or inducible) and hyperreflexia, which differentiate it from neuroleptic malignant syndrome. Onset is rapid (usually within hours) and correlates with starting, increasing, or adding a serotonergic drug. Treatment is primarily supportive: discontinue offending agents, benzodiazepines for agitation and muscle hyperactivity, and cooling for hyperthermia. Cyproheptadine is a specific 5-HT2A antagonist used in moderate-severe cases. Most patients recover fully within 24-72 hours once offending drugs are stopped. This case highlights the importance of drug interaction awareness - tramadol is often overlooked as a serotonergic agent, and many patients don't disclose herbal supplement use.
Clinical Image
Illustration depicting drug interaction awareness. The combination of multiple serotonergic agents, including SSRIs, opioids with serotonin activity (tramadol), and herbal supplements (St. John's Wort), can precipitate life-threatening serotonin syndrome.
Image Source: Wikimedia Commons - "Drug interactions" License: CC BY-SA 4.0 URL: https://commons.wikimedia.org/wiki/File:Drug_interactions.jpg