Influence of Sampling Procedure on Codeine Concentrations in Oral Fluid

Area of Science:

• Pharmacology
• Analytical Chemistry
• Forensic Toxicology

Background:

• Oral fluid (OF) drug analysis faces challenges due to variable OF pH, oral contamination, and sample volume.
• Accurate correlation between plasma and OF drug concentrations is crucial for therapeutic drug monitoring and forensic applications.

Purpose of the Study:

• To compare the oral fluid (OF) to plasma ratio and concentration variability of codeine using two collection systems: Saliva Collection System (SCS) and Quantisal.
• To evaluate the reliability of OF drug measurements for predicting plasma concentrations.

Main Methods:

• 12 volunteers ingested codeine phosphate (19.5 mg).
• Oral fluid (OF) and plasma samples were collected.
• OF was collected using either SCS or Quantisal devices.
• Codeine concentrations were analyzed using gas chromatography-mass spectrometry.

Main Results:

• Mean codeine concentration at 1 hour was 29.8 μg/L in plasma, 72.8 μg/L in SCS OF, and 85.3 μg/L in Quantisal OF.
• The OF/plasma ratio was 2.30 (SCS) and 2.69 (Quantisal).
• Pearson's correlation coefficient (R²) was significantly higher for SCS (0.745) than Quantisal (0.403).

Conclusions:

• The Saliva Collection System (SCS) shows a stronger correlation between oral fluid and plasma codeine concentrations compared to Quantisal.
• SCS appears to be a more reliable method for oral fluid drug concentration analysis, especially for codeine.
• The order of sample collection influenced Quantisal's variability, with reduced variability when used after SCS.