Detection of the synthetic drug 4-fluoroamphetamine (4-FA) in serum and urine

4-Fluoroamphetamine (4-FA) was detected in the blood and urine of two individuals suspected for driving under the influence (DUI). The test for amphetamines in urine subjected to immunoassay screening using the CEDIA DAU assay proved positive. Further investigations revealed a 4-FA cross-reactivity of about 6% in the CEDIA amphetamine assay. 4-FA was qualitatively detected in a general unknown screening for drugs using GC/MS in full scan mode. No other drugs or fluorinated phenethylamines were detected. A validated GC/MS method was established in SIM mode for serum analysis of 4-FA with a limit of detection (LOD) of 1 ng/mL and a lower limit of quantification (LLOQ) of 5 ng/mL. Intra-assay precision was approx. 4% and inter-assay precision approx. 8%. Applying this method, the 4-FA serum concentrations of the two subjects were determined to be 350 ng/mL and 475 ng/mL, respectively. Given the pharmacological data of amphetamine, 4-FA psychoactive effects are to be expected at these serum levels. Both subjects exhibited sympathomimetic effects and psychostimulant-like impairment accordingly.