Instability of Efavirenz Metabolites Identified During Method Development and Validation

Area of Science:

• Pharmacokinetics
• Analytical Chemistry
• Clinical Chemistry

Background:

• Accurate quantification of efavirenz metabolites is essential for understanding efavirenz-related adverse events.
• Existing bioanalytical methods require validation for specific patient populations and sample types.

Purpose of the Study:

• To validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying efavirenz and its metabolites in human plasma.
• To assess the stability of efavirenz and its metabolites under various sample handling and storage conditions.

Main Methods:

• Supported liquid extraction and C18 column chromatography were used for sample preparation and separation.
• Method validation followed US Food and Drug Administration (FDA) bioanalytical guidelines.
• Stability was tested under conditions relevant to clinical sample processing and storage.

Main Results:

• Efavirenz and 8-hydroxyefavirenz demonstrated stability across all tested conditions.
• 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz showed significant degradation (46%-95% loss) under various storage and pre-treatment conditions, including heat.
• Concentrations of 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz were below quantification limits in patient samples pre-treated with heat, likely due to instability.

Conclusions:

• The validated LC-MS/MS method accurately quantifies efavirenz and 8-hydroxyefavirenz.
• 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz are unstable under common sample pre-treatment (heat) and storage conditions, impacting their quantification in patient samples.
• Alternative, non-heat-based sample preparation methods are necessary for accurate measurement of 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz in HIV/AIDS patients.