A 28-year-old man with schizophrenia on haloperidol develops fever, rigidity, altered mental status, and elevated creatine kinase (3500 U/L) over 3 days. Which is the most common causative antipsychotic agent for neuroleptic malignant syndrome?

Explanation

## Most Common Antipsychotic Causing Neuroleptic Malignant Syndrome **Key Point:** Haloperidol, a typical (first-generation) antipsychotic, is the most common antipsychotic agent associated with neuroleptic malignant syndrome (NMS) in clinical practice, despite the availability of newer atypical agents. ### Why Haloperidol is Most Common 1. **Potency of D2 blockade**: Haloperidol has the highest D2 receptor antagonism among all antipsychotics, which is the primary mechanism underlying NMS. 2. **Widespread use**: Despite the advent of atypical antipsychotics, haloperidol remains widely used in acute psychiatric settings, emergency departments, and resource-limited healthcare systems. 3. **Dose-dependent risk**: NMS risk increases with higher doses and rapid dose escalation—common in acute agitation management. 4. **Parenteral formulation**: Haloperidol is frequently administered intramuscularly in acute settings, where rapid onset increases NMS risk. ### Comparative Risk of Antipsychotics for NMS | Antipsychotic | Class | D2 Potency | NMS Risk | Frequency | |---|---|---|---|---| | **Haloperidol** | **Typical** | **Highest** | **Highest** | **Most common** | | Risperidone | Atypical | High | Moderate–High | Common | | Quetiapine | Atypical | Low | Low | Rare | | Aripiprazole | Atypical | Moderate | Low | Rare | **High-Yield:** The classic tetrad of NMS is: **fever + rigidity (lead-pipe) + altered mental status + autonomic instability**. This patient exhibits all four features, with elevated CK confirming muscle breakdown. **Mnemonic:** **FEVER** — **F**irst-generation antipsychotics, **E**levated CK, **V**ery high mortality if untreated, **E**xtra-pyramidal signs, **R**igidity. **Clinical Pearl:** Haloperidol-induced NMS can develop within hours to days of initiation or dose increase. The risk is highest in young males, those with prior NMS episodes, and in acute agitation settings where rapid parenteral dosing is used. **Warning:** ~~Atypical antipsychotics do not cause NMS~~ — while the risk is lower, atypical agents (especially risperidone and paliperidone) can still cause NMS, particularly at high doses or in vulnerable populations. However, haloperidol remains the most common culprit overall. ### Pathophysiology ```mermaid flowchart TD A[Dopamine D2 Blockade]:::action --> B[Disrupted Thermoregulation]:::outcome A --> C[Increased Muscle Tone]:::outcome A --> D[Autonomic Instability]:::outcome B --> E[Fever]:::urgent C --> F[Lead-Pipe Rigidity]:::urgent D --> G[Tachycardia, Hypertension]:::urgent E --> H[Rhabdomyolysis]:::urgent F --> H H --> I[Elevated CK]:::outcome I --> J[Acute Kidney Injury]:::urgent ``` ### Management 1. **Immediate**: Discontinue haloperidol and all antipsychotics. 2. **Supportive care**: Aggressive cooling, IV hydration, monitor urine output. 3. **Pharmacotherapy**: - Dantrolene (skeletal muscle relaxant): 2.5 mg/kg IV, repeat every 5–10 minutes up to 10 mg/kg. - Bromocriptine (dopamine agonist): 2.5–5 mg PO/NG three times daily. 4. **Monitoring**: Serial CK, electrolytes, renal function, coagulation profile. 5. **Rechallenge**: If antipsychotic is necessary, switch to an atypical agent (quetiapine preferred) only after full recovery and a washout period.