# Clinical Cases: CNS Pharmacology

## Case 1: Acetaminophen Overdose

### Clinical Scenario
A 22-year-old female is brought to the emergency department by her roommate after ingesting an unknown quantity of acetaminophen tablets in a suicide attempt approximately 6 hours ago.

### Patient Demographics
- **Age:** 22 years
- **Sex:** Female
- **Weight:** 60 kg

### Chief Complaint
Intentional overdose of acetaminophen 6 hours prior

### History of Present Illness
The patient's roommate found an empty bottle of extra-strength acetaminophen (500 mg tablets, 100 count) and a suicide note. The patient admits to taking "the whole bottle" approximately 6 hours ago following a relationship breakup. She currently has mild nausea and vague abdominal discomfort but is otherwise asymptomatic. She has no other medical problems and takes no other medications.

### Physical Examination
- **Vital Signs:** BP 118/72 mmHg, HR 82 bpm, RR 16, T 36.8C
- **General:** Alert, tearful, cooperative
- **Abdominal:** Mild right upper quadrant tenderness, no guarding or rebound
- **Neurological:** Intact, no asterixis
- **Mental status:** Appropriate, remorseful

### Workup and Results
| Test | Result | Reference Range |
|------|--------|-----------------|
| Acetaminophen level (6 hours post) | 285 mcg/mL | <10 mcg/mL |
| AST | 42 U/L | 10-40 U/L |
| ALT | 38 U/L | 7-56 U/L |
| INR | 1.0 | 0.9-1.1 |
| Creatinine | 0.8 mg/dL | 0.6-1.2 mg/dL |
| Total bilirubin | 0.8 mg/dL | 0.1-1.2 mg/dL |

**Rumack-Matthew nomogram:** Level of 285 mcg/mL at 6 hours is well above the treatment line (150 mcg/mL at 4 hours)

### Diagnosis
**Acute acetaminophen overdose** - estimated ingestion of 50 g (833 mg/kg), high risk for hepatotoxicity

### CNS Pharmacology Principles Illustrated
1. **NAPQI formation:** Acetaminophen is metabolized by CYP2E1 to toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI).
2. **Glutathione depletion:** Normally, glutathione conjugates NAPQI. In overdose, glutathione is depleted, allowing NAPQI to bind cellular proteins.
3. **Zone 3 necrosis:** Centrilobular hepatocyte necrosis due to highest CYP450 concentration in zone 3.
4. **N-acetylcysteine mechanism:** NAC replenishes glutathione and provides alternative substrate for NAPQI detoxification.
5. **Timing critical:** NAC is nearly 100% hepatoprotective if given within 8 hours.

### Treatment
1. **N-acetylcysteine (NAC):** Start immediately - IV protocol:
   - Loading: 150 mg/kg in 200 mL D5W over 1 hour
   - Second infusion: 50 mg/kg in 500 mL D5W over 4 hours
   - Third infusion: 100 mg/kg in 1000 mL D5W over 16 hours
2. **Activated charcoal:** 50 g PO if within 4 hours (may still have benefit at 6 hours)
3. **Serial labs:** LFTs, INR, creatinine every 6-12 hours
4. **Monitor for hepatotoxicity:** Peak liver injury typically 72-96 hours post-ingestion
5. **Psychiatric consultation** once medically cleared
6. **Suicide precautions**

### Clinical Image

![Rumack-Matthew Nomogram](case_01_image.jpg)

*The Rumack-Matthew nomogram plots acetaminophen serum concentration against time since ingestion. Levels above the treatment line indicate risk of hepatotoxicity and need for N-acetylcysteine therapy.*

**Image Source:** Wikimedia Commons
**License:** Public Domain
**URL:** https://commons.wikimedia.org/wiki/File:Rumack-Matthew_nomogram.svg

---

## Case 2: Opioid Overdose

### Clinical Scenario
A 28-year-old male is found unresponsive by EMS in a parking lot with drug paraphernalia nearby.

### Patient Demographics
- **Age:** 28 years
- **Sex:** Male
- **Weight:** 70 kg (estimated)

### Chief Complaint
Found unresponsive

### History of Present Illness
EMS was called for an unresponsive male. Bystanders report the patient was seen injecting something into his arm before becoming unresponsive over approximately 5 minutes. A used syringe and small bags with white powder residue were found nearby. No medical history available.

### Physical Examination
- **Vital Signs:** BP 85/52 mmHg, HR 52 bpm, RR 4 (shallow), T 35.6C, SpO2 78% on RA
- **General:** Unresponsive, cyanotic
- **HEENT:** Miosis (1 mm bilaterally, "pinpoint pupils")
- **Respiratory:** Severely diminished breath sounds, no chest wall movement
- **Cardiovascular:** Bradycardic, weak pulses
- **Neurological:** GCS 3 (no eye opening, no verbal, no motor response)
- **Skin:** Cool, mottled, injection sites on bilateral antecubital fossae

### Prehospital Treatment
- Bag-mask ventilation initiated
- Intranasal naloxone 4 mg administered by EMS
- Patient began breathing spontaneously within 2 minutes

### Workup and Results
| Test | Result | Reference Range |
|------|--------|-----------------|
| Urine drug screen | Positive for opiates, fentanyl | Negative |
| Blood glucose | 95 mg/dL | 70-100 mg/dL |
| Arterial blood gas | pH 7.18, PaCO2 72, PaO2 58 | - |
| Lactate | 4.8 mmol/L | 0.5-2.0 mmol/L |

### Diagnosis
**Opioid overdose** - likely fentanyl/heroin mixture based on clinical presentation and drug screen

### CNS Pharmacology Principles Illustrated
1. **Mu receptor effects:** Opioids produce the classic triad of CNS depression, respiratory depression, and miosis through mu receptor activation.
2. **Respiratory depression mechanism:** Opioids reduce brainstem sensitivity to CO2, causing hypoventilation.
3. **Naloxone mechanism:** Competitive mu receptor antagonist that rapidly displaces opioids from receptors.
4. **Short duration of naloxone:** Half-life 30-90 minutes, much shorter than most opioids - risk of re-sedation.
5. **Fentanyl potency:** Synthetic opioid approximately 100x more potent than morphine, requiring higher naloxone doses.

### Treatment
1. **Airway management:** Bag-mask ventilation, consider intubation if no response to naloxone
2. **Naloxone:** 0.4-2 mg IV/IM/IN, repeat every 2-3 minutes as needed
   - Goal: Restore adequate respirations, not full consciousness
   - Titrate to avoid precipitating severe withdrawal
3. **Continuous monitoring:** High risk for re-sedation, especially with long-acting opioids or fentanyl analogs
4. **Naloxone infusion:** Consider 2/3 of reversal dose per hour if repeated doses needed
5. **Observation:** Minimum 4-6 hours; longer for extended-release opioids or methadone
6. **Addiction medicine consultation** and harm reduction education
7. **Prescribe take-home naloxone** upon discharge

### Clinical Image

![Opioid Pills](case_02_image.jpg)

*Various opioid medications. Opioid overdose has become a leading cause of death in young adults, with synthetic opioids like fentanyl increasingly implicated.*

**Image Source:** Wikimedia Commons
**License:** Public Domain
**URL:** https://commons.wikimedia.org/wiki/File:Opioids.jpg

---

## Case 3: Serotonin Syndrome

### Clinical Scenario
A 45-year-old female presents with agitation, tremor, and fever after her psychiatrist added tramadol to her existing sertraline regimen.

### Patient Demographics
- **Age:** 45 years
- **Sex:** Female
- **Weight:** 68 kg

### Chief Complaint
Confusion, shakiness, and feeling "overheated" for 8 hours

### History of Present Illness
The patient has major depressive disorder treated with sertraline 150 mg daily for 2 years. Three days ago, her psychiatrist added tramadol 50 mg three times daily for chronic low back pain. She began experiencing restlessness, profuse sweating, and muscle twitching yesterday, which have worsened today. Her husband notes she seems confused and has had diarrhea.

### Medications
- Sertraline 150 mg daily
- Tramadol 50 mg TID (started 3 days ago)

### Physical Examination
- **Vital Signs:** BP 165/95 mmHg, HR 118 bpm, RR 22, T 39.8C
- **General:** Agitated, diaphoretic, confused
- **HEENT:** Mydriasis (6 mm bilaterally), dry mucous membranes
- **Neurological:**
  - Hyperreflexia (3+ throughout)
  - Spontaneous clonus at ankles bilaterally
  - Muscle rigidity (legs > arms)
  - Tremor
  - Ocular clonus present
- **Abdominal:** Hyperactive bowel sounds, diarrhea
- **Skin:** Diaphoretic, flushed

### Workup and Results
| Test | Result | Reference Range |
|------|--------|-----------------|
| WBC | 14,500/mcL | 4,500-11,000/mcL |
| CK | 1,850 U/L | 30-170 U/L |
| Creatinine | 1.4 mg/dL | 0.6-1.2 mg/dL |
| TSH | 1.8 mIU/L | 0.4-4.0 mIU/L |
| Urine drug screen | Positive for amphetamines | - |

Note: Tramadol cross-reacts with amphetamine immunoassays

### Diagnosis
**Serotonin syndrome** - Hunter Criteria met (serotonergic agent + spontaneous clonus)

### CNS Pharmacology Principles Illustrated
1. **Serotonin excess:** Tramadol inhibits serotonin reuptake (like an SSRI) while sertraline does the same, causing excessive synaptic serotonin.
2. **Hunter Criteria:** More specific than older criteria; clonus is central to diagnosis.
3. **Neuromuscular excitation:** Hyperreflexia, clonus, tremor, and rigidity distinguish from other conditions.
4. **Drug combinations:** SSRI + tramadol, SSRI + MAOI, or SSRI + triptans are high-risk combinations.
5. **Rapid onset:** Typically develops within 24 hours of drug change.

### Treatment
1. **Discontinue all serotonergic agents** immediately
2. **Supportive care:**
   - Cooling measures for hyperthermia
   - IV fluids for dehydration
   - Benzodiazepines (lorazepam 2 mg IV) for agitation and muscle rigidity
3. **Cyproheptadine:** 12 mg PO initial dose, then 2 mg every 2 hours for ongoing symptoms (serotonin antagonist)
4. **Consider intubation** if severe hyperthermia or rigidity
5. **Avoid restraints** (can worsen hyperthermia)
6. **Monitor CK and renal function** for rhabdomyolysis
7. **Symptoms typically resolve within 24-72 hours** with supportive care

### Key Differential Diagnosis

| Feature | Serotonin Syndrome | Neuroleptic Malignant Syndrome |
|---------|-------------------|-------------------------------|
| Onset | Rapid (hours) | Gradual (days) |
| Reflexes | Hyperreflexia, clonus | Hyporeflexia |
| Rigidity | Legs > arms | Lead-pipe, generalized |
| Pupils | Mydriasis | Normal |
| Bowel sounds | Hyperactive | Decreased |
| Causative agent | Serotonergic drugs | Dopamine antagonists |