Interconversion between haloperidol and reduced haloperidol in healthy volunteers.

Area of Science:

• Pharmacokinetics and Drug Metabolism
• Neuroscience and Pharmacology

Background:

• Haloperidol (HAL) is a widely used antipsychotic medication.
• Understanding the metabolic fate and interconversion of HAL and its reduced form, RHAL, is crucial for optimizing therapeutic outcomes.
• Previous studies suggest potential interconversion, but detailed pharmacokinetic analysis is needed.

Purpose of the Study:

• To investigate the in vivo interconversion between haloperidol (HAL) and reduced haloperidol (RHAL) after single oral administration.
• To quantify the direction and extent of this interconversion in healthy human volunteers.
• To compare the pharmacokinetic disposition of HAL and RHAL following separate administrations.

Main Methods:

• A crossover study design involving 15 healthy young male volunteers.
• Administration of low single oral doses (5 mg) of either HAL or RHAL.
• Ultrasensitive High-Performance Liquid Chromatography (HPLC) method for plasma concentration monitoring of both analytes over one week.
• Analysis of Area Under the Curve (AUC(0-t)) ratios to determine interconversion extent.

Main Results:

• Interconversion between HAL and RHAL was observed in nearly all volunteers, indicating significant metabolic linkage.
• The interconversion process predominantly favors the reduction of HAL to RHAL.
• Pharmacokinetic disposition of HAL administered as RHAL was formation-rate limited, while RHAL disposition after HAL administration was significantly slower than that of HAL itself.

Conclusions:

• Significant in vivo interconversion occurs between haloperidol and reduced haloperidol in humans.
• The metabolic pathway favors the reduction of haloperidol to its less active reduced form.
• Understanding this interconversion is vital for interpreting pharmacokinetic data and potential drug interactions involving haloperidol.