Gamma-hydroxybutyrate (GHB) is a common drug of abuse with an elimination half-life of 20-45?min. However, there is some evidence that GHB might exhibit saturation kinetics after ingesting high recreational doses. The aim of this study was to investigate the elimination kinetics of GHB from blood in people apprehended by the police for impaired driving and secondary to describe concentrations in all GHB-positive drivers.
Two consecutive blood samples were taken about 30-40?min apart from N?=?16 apprehended drivers in Norway. GHB was determined in blood by an Ultra High-Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) method. The changes in GHB between the two consecutive blood samples allowed estimating GHB's elimination half-life, assuming first-order and zero-order elimination kinetics. GHB concentrations are also reported for N?=?1276 apprehended drivers with GHB in blood.
The median time interval between collecting the two blood samples was 36?min (range 20-56?min). The median concentration of GHB in the first blood sample was 56.5?mg/L (range 14.1-142?mg/L) compared with 47.8?mg/L in the second sample (range 9.75-113?mg/L). The median elimination half-life was 103?min (range 21-187?min), and GHB's median zero-order elimination rate constant was 21.0?mg/L/h (range 6.71-45.4?mg/L/h). Back-calculation to the time of driving resulted in GHB concentrations up to 820?mg/L assuming first-order kinetics and up to 242?mg/L assuming zero-order kinetics. In all drivers (N?=?1276), the median GHB concentration was 73.7?mg/L and highest was 484?mg/L.
The elimination half-life of GHB in blood samples from apprehended drivers was longer than expected compared with results of controlled dosing studies. Zero-order kinetics seems a more appropriate model for GHB when concentrations are back-calculated, and the median elimination rate was 21?mg/L/h.