Evaluating the hip-flask defence in subjects with alcohol on board: An experimental study Christoffer Kronstrand a , Gunnel Nilsson a , Maria D. Chermà a , Johan Ahlner a,b , Fredrik C. Kugelberg a,b , Robert Kronstrand a,b, * a Department of Forensic Genetics and Forensic Toxicology, National Board of Forensic Medicine, Linköping, Sweden b Division of Drug Research, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden A R T I C L E I N F O Article history: Received 10 June 2018 Received in revised form 12 November 2018 Accepted 18 November 2018 Available online 26 November 2018 Keywords: Alcohol Ethanol Kinetics Hip-flask defence DUI Controlled dosing A B S T R A C T Driving under the influence of alcohol is a major problem for traffic-safety and a popular defence argument is alleged consumption after driving, commonly referred to as the hip-flask defence. Forensic toxicologists are often called as expert witnesses in drinking and driving cases where the suspect has claimed the hip-flask defence, to assess the credibility of the explanation. Several approaches to help the expert have been introduced but the scientific data used to support or challenge this is solely based on data from controlled single doses of ethanol administered during a short time and in abstinent subjects. In reality, we believe that even in drinking after driving cases, the subject many times has alcohol on board at time of the hip-flask drink. This questions the applicability of the data used as basis to investigate the hip-flask defence. To fill this knowledge gap, we aimed to investigate how blood and urine ethanol kinetics vary after an initial drinking session of beer and then a subsequent hip-flask drink of three different doses of whiskey. Fifteen subjects participated in the study and each provided 10 urine samples and 17 blood samples over 7 h. The initial drink was 0.51 g ethanol/kg and the second was either 0.25, 0.51, or 0.85 g/kg. Our data suggested that the difference between the ethanol concentrations in two consecutive urine samples is a more sensitive parameter than the ratio between urine and blood alcohol to detect a recent intake when ethanol from previous intakes are already present in the body. Twelve subjects presented results that fully supported a recent intake using the criteria developed from a single intake of ethanol. Three subjects showed unexpected results that did not fully support a recent intake. We conclude that data from one blood sample and two urine samples provide good evidence for investigating the hip-flask defence even if alcohol was on board at the time of the hip-flask drink. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Driving under the influence of alcohol (DUI) is a major problem for traffic-safety. Drunk drivers are over-represented in statistics of injuries and deaths on the road. Among alcohol-impaired drivers a popular defence argument is alleged consumption after driving, commonly referred to as the hip-flask defence [1,2]. In such cases the analysis and interpretation of a person’s blood-alcohol concentration (BAC) and urine alcohol concentration (UAC) are important tasks for forensic toxicologists. Therefore, knowledge about the pharmacokinetics of alcohol is important. There is a considerable variation in pharmacokinetics of ethanol both within and between subjects [3,4,5]. In one study, the variation in mean maximum ethanol concentration (Cmax) was 23% between subjects and 24% within subject when subjects were fasted. Corresponding figures for the mean area under the ethanol concentration-time curve (AUC) were 21 and 22%, respectively [5] . In addition, both the absorption and elimination are affected by a number of factors, e.g. type of beverage, nutritional state, age, sex, body weight and genetic factors [4] . The speed of absorption of ethanol from the gut, which has bearing on the peak concentration of alcohol, depends on e.g. the concentration of ethanol in the beverage and in particular the fed or fasting state of the individual [5,6]. In the above mentioned study [5], where 0.3 g ethanol/kg was given the Cmax in the fasting state was significantly greater than after a meal, 39.9 mg/ dL vs 21.3 mg/dL. The same applied to the mean AUC, 54.8 mg/dL h vs 33.6 mg/dL h. Ethanol is distributed into the total body water and hence differences in age, sex and bodyweight will affect the concentration-time profile of ethanol [7]. The enzymes mainly responsible for the metabolism of ethanol are under genetic * Corresponding author at: Department of Forensic Genetics and Forensic Toxicology, National Board of Forensic Medicine, Linköping, Sweden. E-mail address: robert.kronstrand@rmv.se (R. Kronstrand). https://doi.org/10.1016/j.forsciint.2018.11.014 0379-0738/© 2018 Elsevier B.V. All rights reserved. Forensic Science International 294 (2019) 189–195 Contents lists available at ScienceDirect Forensic Science International journal homepage: www.elsevier.com/locat e/f orsciint