What is the starting intramuscular (IM) dose of Thorazine (chlorpromazine) for acute psychosis?

Starting IM Dose of Thorazine for Acute Psychosis

The starting intramuscular dose of chlorpromazine (Thorazine) for acute psychosis in adults is 25 mg, which may be repeated with an additional 25-50 mg in 1 hour if necessary. 1

Adult Dosing for Acute Psychotic States

For hospitalized patients experiencing acute schizophrenic or manic states, the FDA-approved dosing regimen is:

• Initial dose: 25 mg IM (1 mL) 1
• Repeat dosing: Additional 25-50 mg IM in 1 hour if necessary 1
• Dose escalation: Increase subsequent IM doses gradually over several days, up to 400 mg every 4-6 hours in exceptionally severe cases, until patient is controlled 1
• Expected response: Most patients become quiet and cooperative within 24-48 hours, at which point oral doses may be substituted 1

Alternative Prompt Control Regimen

For prompt control of severe symptoms in less acute presentations:

• Initial dose: 25 mg IM 1
• Repeat if necessary in 1 hour 1
• Transition: Subsequent doses should be oral, 25-50 mg three times daily 1

Critical Safety Considerations

Monitor for hypotension before increasing parenteral dosage—this is the primary dose-limiting factor. 1 Chlorpromazine can cause significant hypotension and dystonic reactions, particularly with repeated doses. 2

Important Precautions:

• Elderly patients require lower starting doses in the lower range of dosing recommendations, as they are more susceptible to hypotension and neuromuscular reactions 1
• Debilitated or emaciated patients require more gradual dose escalation 1
• QTc prolongation risk: Repeated doses can prolong the QT interval and precipitate torsades de pointes 2

Context Within Current Treatment Paradigms

While chlorpromazine remains FDA-approved for acute psychosis, contemporary emergency department guidelines favor alternative agents. Haloperidol has the strongest evidence base among conventional antipsychotics for acute agitation, typically dosed at 5 mg IM. 2 Atypical antipsychotics like ziprasidone 20 mg IM demonstrate superior tolerability with fewer movement disorders compared to conventional agents. 2

The historical practice of "rapid neuroleptization" with high-dose loading strategies has fallen out of favor due to increased side effects without improved efficacy. 3, 4 Hourly intramuscular injections of chlorpromazine can achieve tranquilization within 6 hours or less, but this approach carries higher risk of extrapyramidal symptoms. 5

Pediatric Dosing (6 months to 12 years)

For severe behavioral problems in hospitalized children:

• Dose: 0.25 mg/lb (0.55 mg/kg) body weight IM every 6-8 hours as needed 1
• Maximum daily IM dose: 40 mg/day for children up to 5 years or 50 lbs; 75 mg/day for children 5-12 years or 50-100 lbs, except in unmanageable cases 1
• Caution: All doses may cause paradoxical excitement or agitation in pediatric patients 6

Common Pitfalls to Avoid

• Do not increase dosage if hypotension has occurred—this is explicitly contraindicated 1
• Avoid in organic psychoses or anticholinergic toxicity, as chlorpromazine's anticholinergic properties can worsen agitation 2
• Do not use in hallucinogen-induced psychosis except as last resort 5
• Screen for organic brain syndrome (clouded sensorium, disorientation, poor recent memory) before administration 5