What is the maximum recommended one-time dose of intramuscular (IM) Thorazine (chlorpromazine)?

Maximum One-Time Dose of IM Thorazine (Chlorpromazine)

The maximum one-time intramuscular (IM) dose of Thorazine (chlorpromazine) is 50 mg for adults in most clinical scenarios, with the potential to increase to 400 mg every 4-6 hours in exceptionally severe cases of acute schizophrenia or mania in hospitalized patients. 1

Adult Dosing Guidelines

Standard Dosing

• Initial IM dose is typically 25 mg (1 mL) for most indications 1
• If necessary, an additional 25-50 mg can be administered after 1 hour if the initial dose is insufficient 1
• For nausea and vomiting, 25-50 mg can be given every 3-4 hours as needed, if no hypotension occurs 1

Maximum Dosing by Indication

• Acute Schizophrenic or Manic States (Hospitalized Patients):

  • Initial dose: 25 mg IM
  • Can increase subsequent IM doses gradually over several days
  • Maximum dose: Up to 400 mg every 4-6 hours in exceptionally severe cases 1

• Nausea and Vomiting:

  • 25-50 mg every 3-4 hours as needed 1

• Presurgical Apprehension:

  • 12.5-25 mg, 1-2 hours before operation 1

• Intractable Hiccups:

  • 25-50 mg IM 1

• Acute Intermittent Porphyria:

  • 25 mg three or four times daily 1

• Tetanus:

  • 25-50 mg three or four times daily 1

Pediatric Dosing Guidelines

• Children 6 months to 12 years:
  • 0.25 mg/lb body weight every 6-8 hours as needed 1
  • Maximum daily IM dosage:
    • Children up to 5 years (or 50 lbs): Not over 40 mg/day
    • Children 5-12 years (or 50-100 lbs): Not over 75 mg/day except in severe cases 1

Important Administration Considerations

• Inject slowly, deep into the upper outer quadrant of buttock 1
• Keep patient lying down for at least 30 minutes after injection due to possible hypotensive effects 1
• Reserve parenteral administration for bedfast patients or acute ambulatory cases 1
• If irritation occurs, dilution with saline or 2% procaine may help 1
• Avoid subcutaneous injection 1

Adverse Effects and Precautions

• Monitor for hypotension, especially in elderly patients who are more susceptible 1
• Watch for extrapyramidal symptoms, which can occur at higher doses 2
• Be alert for potential upper airway compromise due to laryngeal-pharyngeal dystonia, which is dose-dependent 3
• Rapid IV administration may precipitate seizures; IV route is only indicated for severe hiccups, surgery, and tetanus 1
• All doses may cause paradoxical excitement or agitation 4

Special Populations

• Elderly patients should be observed more closely for hypotension and neuromuscular reactions 1
• Dosage should be increased more gradually in elderly patients 1
• Chlorpromazine should generally not be used in pediatric patients under 6 months of age except in potentially life-saving situations 1

The FDA drug label provides the most authoritative guidance on maximum dosing, indicating that while 25-50 mg is the standard one-time IM dose for most indications, doses can be increased up to 400 mg every 4-6 hours in exceptionally severe cases of psychiatric disorders in hospitalized patients 1.