The concentration of oxazepam and oxazepam glucuronide in oral fluid, blood and serum after controlled administration of 15 and 30 mg oxazepam

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Concentration–time profiles of drugs in oral fluid generally run parallel to those in blood. • In general, oral fluid contains more parent drug than metabolites. • For some benzodiazepines it has been shown that concentrations are lower in oral fluid than in blood. WHAT THIS STUDY ADDS • The concentration–time profile of oxazepam in oral fluid after a single dose of oxazepam runs parallel to blood and is dose dependent. • Concentration ratios (oral fluid/blood and oral fluid/serum) of oxazepam and oxazepam glucuronide after controlled intake of a single dose of oxazepam are presented. AIMS To measure and compare the concentration–time profiles of oxazepam and oxazepam glucuronide in blood, serum and oral fluid within the scope of roadside testing. METHODS Biological samples were collected from eight male subjects after ingestion of 15 or 30 mg oxazepam on separate dosing occasions with an interval of 7 days. The concentration–time profiles of oxazepam and oxazepam glucuronide were fitted by using a one‐compartment model. RESULTS For oxazepam and oxazepam glucuronide, the mean oral fluid/blood ratios were 0.05 (range 0.04–0.07) and 0.004 (range 0.002–0.006), respectively. The concentration–time profiles in oral fluid paralleled those in blood. CONCLUSION After oral administration of therapeutic doses of oxazepam, concentrations in oral fluid are very much lower than those in blood, and those of oxazepam glucuronide are much lower than those of the parent compound. Nevertheless, assay of oral fluid for oxazepam can be used to detect recent ingestion of the drug in drivers suspected of impaired driving performance.