What is the peak action duration of haloperidol (antipsychotic medication)?

Peak Action and Duration of Haloperidol

Haloperidol achieves peak plasma concentrations within 20-40 minutes after intramuscular administration and within 2-6 hours after oral administration, with clinical effects typically evident within 30 minutes for IM dosing. 1

Intramuscular (IM) Administration

• IM haloperidol produces clinical sedation and behavioral control within 30 minutes in approximately 83% of agitated patients, making it highly effective for acute management of disruptive behavior 1
• Peak plasma concentrations occur within the first hour after IM injection, with maximal clinical effect typically achieved between 20-40 minutes 1
• The onset of action is 1-2 minutes when given intravenously, though this route carries higher risk of QTc prolongation and should be avoided when possible 2, 3

Oral Administration

• Oral haloperidol has a bioavailability of 60-65% due to first-pass metabolism 4
• Peak plasma levels occur 2-6 hours after oral dosing 4
• Clinical effects may be evident within 1-2 hours, though full therapeutic response develops more gradually than with parenteral administration 4

Duration of Action

• The elimination half-life of haloperidol ranges from 12-38 hours, with significant interindividual variability 4
• Clinical duration of effect for a single IM dose typically lasts 4-8 hours, though this varies based on dose and individual patient factors 1
• Steady-state plasma concentrations are achieved after approximately 4-7 days of regular dosing 4

Long-Acting Injectable (Haloperidol Decanoate)

• Haloperidol decanoate exhibits a "flip-flop" pharmacokinetic profile where absorption is slower than elimination 4
• Peak plasma concentrations occur 3-7 days after IM injection of the decanoate formulation 5, 4
• The elimination half-life is approximately 3 weeks (21 days), justifying monthly administration intervals 5, 6
• Steady-state is reached after approximately 3 months of monthly injections 5, 4

Important Clinical Considerations

• Haloperidol causes a mean QTc prolongation of 7 ms, with higher risk when administered intravenously 2, 3
• The American Academy of Pediatrics recommends preferring oral or intramuscular routes over intravenous administration to minimize cardiac risk 3
• Extrapyramidal symptoms (EPS) are common adverse effects that may occur within hours to days of initiation 2
• Patients should be monitored for at least 2 hours after administration for respiratory depression and cardiovascular effects, particularly when combined with other sedating medications 2

Dosing Conversion

• When transitioning from oral to decanoate formulation, the conversion ratio ranges from 10:1 to 15:1 (mean 14:1), meaning a patient on 10 mg/day oral would require approximately 140 mg decanoate monthly 7, 6
• Switch to oral haloperidol as soon as acute agitation resolves, typically after 24-48 hours of controlled behavior 8