A 28-year-old man with schizophrenia on haloperidol develops high fever (40.2°C), severe muscle rigidity, altered mental status, and elevated CK (1200 U/L) over 3 days. Which drug is the first-line treatment for neuroleptic malignant syndrome in this patient?

Explanation

## Management of Neuroleptic Malignant Syndrome (NMS) **Key Point:** Dantrolene sodium is the first-line pharmacological agent for NMS. It is a skeletal muscle relaxant that acts on the sarcoplasmic reticulum to reduce intracellular calcium release, directly addressing the pathophysiology of NMS. ## Mechanism of NMS and Dantrolene Action NMS is caused by: - **Dopamine D~2~ receptor blockade** in the hypothalamus and basal ganglia - **Loss of thermoregulation** and **increased muscle tone** leading to uncontrolled heat production - **Rhabdomyolysis** from sustained muscle contraction Dantrolene works by: 1. Inhibiting calcium release from the sarcoplasmic reticulum via the ryanodine receptor 2. Reducing muscle contractility and heat generation 3. Preventing progression to fulminant rhabdomyolysis and acute kidney injury ## Dosing and Administration **High-Yield:** Standard NMS management regimen: - **Dantrolene:** 1 mg/kg IV bolus, repeated every 5–10 minutes up to 10 mg/kg total (or until symptom resolution) - **Maintenance:** 1 mg/kg IV every 4–6 hours for 24–48 hours after symptom resolution - **Oral continuation:** 1 mg/kg PO four times daily for 5–7 days ## Combination Therapy: Dantrolene + Bromocriptine | Agent | Mechanism | Role in NMS | |-------|-----------|-------------| | **Dantrolene** | Skeletal muscle relaxant (↓ Ca²⁺ release) | **First-line**: Acute muscle rigidity, hyperthermia, rhabdomyolysis | | **Bromocriptine** | D~2~ agonist (restores dopaminergic tone) | **Adjunctive**: Speeds recovery, reduces recurrence; started after dantrolene | **Clinical Pearl:** While bromocriptine (5–15 mg/day in divided doses) is often used **in combination** with dantrolene, **dantrolene alone is the single most critical agent** for acute NMS because it immediately halts the muscle hypermetabolism and prevents organ failure. ## Supportive Care (Essential) 1. **Immediate:** Discontinue all antipsychotics 2. **Cooling:** Ice packs, cooling blankets, cold IV fluids 3. **Hydration:** Aggressive IV fluids (target urine output 200–300 mL/hr) to prevent acute kidney injury from myoglobinuria 4. **Monitoring:** Hourly vitals, CK, creatinine, potassium, urine myoglobin 5. **Complications:** Treat hyperkalemia, acidosis, DIC as needed ## Differential: NMS vs. Serotonin Syndrome | Feature | NMS | Serotonin Syndrome | |---------|-----|--------------------| | **Onset** | Days to weeks | Hours to days | | **Causative agents** | Antipsychotics (D~2~ antagonists) | SSRIs, tramadol, MAOIs, linezolid | | **Specific treatment** | **Dantrolene** + bromocriptine | Cyproheptadine | | **Hyperreflexia** | May be absent or mild | Prominent | | **GI symptoms** | Rare | Common (diarrhea) | | **Mydriasis** | Absent | Often present | | **Muscle rigidity** | "Lead pipe" or "cogwheel" | Variable | **Warning:** Do NOT use cyproheptadine for NMS — it is ineffective because the problem is dopamine deficiency, not serotonin excess. ## Why Dantrolene Is First-Line 1. **Direct effect on muscle physiology** — stops the heat-generating mechanism immediately 2. **Prevents rhabdomyolysis progression** — reduces CK rise and kidney injury risk 3. **Rapid symptom resolution** — fever and rigidity improve within 24–48 hours 4. **Evidence-based** — multiple case series and guidelines support dantrolene monotherapy as effective 5. **Bromocriptine is adjunctive** — useful but not essential for acute management [cite:Harrison 21e Ch 459; KD Tripathi 8e Ch 12]