Interpretation of oxycodone concentrations in oral fluid

The purpose of this retrospective study was to compare oxycodone concentrations in saliva and whole blood with a view to propose therapeutic concentrations in oral fluid. Oral fluid is an easy specimen to collect with several advantages over urine, including ease of collection and difficulty of adulteration. As oral fluid is a reflection of free drug circulating in the blood, drug concentrations in saliva are more closely related to blood levels than urine concentrations. The number of testing laboratories offering the analysis of prescription pain medications in urine has increased significantly over the last few years, along with the overuse and abuse of pain killing drugs, specifically oxycodone. Hence, the utility of oral fluid analysis in this field was assessed.

Paired specimens of blood and oral fluid were retrospectively studied in an attempt to establish a range for oxycodone concentrations in oral fluid reflective of therapeutic intake. Twenty-three paired oral fluid-blood specimens were studied. Oral fluid samples had been collected with the Quantisal™ oral fluid device, stored cold and shipped overnight to the laboratory prior to testing. Blood specimens were collected simultaneously in gray top tubes.

From 23 pairs of samples, the median concentration in oral fluid was 524 μg/L and blood was 53 μg/L. The whole blood to plasma ratio for oxycodone was 1.3, so the median plasma concentration was 41 μg/L projecting a saliva to plasma ratio (S:P ratio) of 12. The comparison of oral fluid-blood concentrations allowed the projection of a S:P ratio for oxycodone and the development of a potential therapeutic range for oxycodone in oral fluid.

Saliva drug concentrations in pain management are more closely related to blood levels than urine so can be more easily interpreted. These data provide a foundation for interpretative advances; however, further research surrounding other pain medications and controlled studies are necessary.