Is Thorazine (chlorpromazine) 12.5 mg intramuscularly (IM) safe for a 14-year-old's agitation?

Chlorpromazine 12.5 mg IM for Adolescent Agitation: Safety Assessment

Chlorpromazine 12.5 mg IM can be used safely in a 14-year-old for agitation, as this dose falls within FDA-approved pediatric dosing guidelines, though alternative agents with better safety profiles should be strongly considered first.

FDA-Approved Pediatric Dosing

The FDA label explicitly permits chlorpromazine use in pediatric patients 6 months to 12 years of age, with dosing extending to adolescents for severe behavioral problems 1:

• For severe behavioral problems (IM): 0.25 mg/lb (approximately 0.55 mg/kg) every 6-8 hours as needed 1
• Maximum IM dosage for 50-100 lbs: Not to exceed 75 mg/day except in unmanageable cases 1
• For a 14-year-old (typically >100 lbs): Higher doses may be used, with hospitalized patients receiving 25-50 mg IM initially, repeated in 1 hour if necessary 1

The 12.5 mg dose is well below the typical starting dose of 25 mg IM for acute agitation in adolescents and adults, making it a conservative choice from a dosing perspective 1.

Critical Safety Considerations

Cardiovascular Monitoring Required

• Hypotension risk: Chlorpromazine causes significant hypotension, particularly with IM administration 1, 2
• Keep patient lying down for at least 30 minutes post-injection 1
• QTc prolongation: All antipsychotics, including chlorpromazine, can cause quinidine-like QTc prolongation leading to torsades de pointes 3
• Obtain baseline ECG if possible, especially if patient has cardiac risk factors or is on other QT-prolonging medications 3

Drug-Drug Interactions

• 38% of chlorpromazine administrations in one pediatric study resulted in drug-drug interactions 4
• Check for concurrent medications that prolong QT interval (macrolides, antiemetics, other antipsychotics, antihistamines) 3
• Avoid in patients with anticholinergic drug intoxication (hallucinogens, anticholinergic delirium) 3

Neurological Adverse Effects

• Extrapyramidal symptoms (EPS): Dystonic reactions, akathisia, and parkinsonism are common 3, 2
• Have diphenhydramine 1-2 mg/kg IV/IM available for acute dystonic reactions 3
• Seizure risk: Chlorpromazine lowers seizure threshold; one case of status epilepticus reported in comparative trial 2
• Avoid in patients with history of seizure disorder or traumatic brain injury 5

Paradoxical Effects

• Chlorpromazine-induced psychosis and worsening agitation can occur, particularly in patients with organic brain disorders 5
• 14% of administrations were ineffective for managing agitation in one pediatric study 4
• 35% of administrations resulted in side effects possibly caused by chlorpromazine 4

Preferred Alternative Agents

Current pediatric emergency guidelines recommend other agents over chlorpromazine for acute agitation 3:

First-Line Combinations (Preferred)

• Haloperidol + diphenhydramine 3
• Risperidone + lorazepam or midazolam 3
• Risperidone + diphenhydramine 3

Why Alternatives Are Preferred

• Better side effect profile: Lower risk of hypotension and sedation compared to chlorpromazine 3, 6
• More predictable response: Higher-potency antipsychotics (haloperidol) or atypical antipsychotics (risperidone) have supplanted chlorpromazine for acute agitation 6
• Combination therapy more effective: Antipsychotic plus benzodiazepine may be more effective than either alone 3

Administration Protocol If Chlorpromazine Is Used

1. Pre-administration assessment:

   • Verify no contraindications (seizure history, TBI, anticholinergic toxicity) 5
   • Check medication list for QT-prolonging drugs 3
   • Obtain baseline vital signs and ECG if feasible 3

2. During administration:

   • Inject slowly, deep into upper outer quadrant of buttock 1
   • Never inject undiluted into vein 1
   • Consider diluting with saline or 2% procaine if irritation is a concern 1

3. Post-administration monitoring:

   • Keep patient supine for minimum 30 minutes 1
   • Monitor vital signs every 15 minutes for first hour 3
   • Continuous observation for respiratory depression, hypotension, and EPS 3
   • Have reversal agents available (diphenhydramine for dystonia) 3

4. Repeat dosing:

   • If needed, can repeat 12.5-25 mg in 1 hour if no hypotension occurs 1
   • Transition to oral dosing once patient controlled 1

Common Pitfalls to Avoid

• Do not use in outpatient/ambulatory settings - reserve for bedfast patients due to hypotension risk 1
• Do not combine with multiple sedating agents without careful monitoring - increases respiratory depression risk 3
• Do not use routinely - where better-evaluated alternatives are available, avoid chlorpromazine 2
• Do not ignore drug interactions - 38% incidence in real-world pediatric use 4
• Do not use in patients with developmental disabilities without extreme caution - higher risk of paradoxical agitation 3

Clinical Bottom Line

While 12.5 mg IM chlorpromazine is within safe dosing parameters for a 14-year-old and represents a conservative dose, modern evidence supports using alternative agents (haloperidol, risperidone) with or without benzodiazepines as first-line therapy for acute agitation 3, 6. If chlorpromazine must be used due to limited alternatives, strict adherence to monitoring protocols is essential, particularly for hypotension and cardiac effects 1, 2.