Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework

Abstract

Reliable information about the elimination rate of alcohol (ethanol) from blood is often needed in forensic science and legal medicine when alcohol-related crimes, such as drunken driving or drug-related sexual assault are investigated. A blood sample for forensic analysis might not be taken until several hours after an offence was committed. The courts usually want to know the suspect's blood-alcohol concentration (BAC) at some earlier time, such as the time of driving. Making these back calculations or retrograde extrapolations of BAC in criminal cases has many proponents and critics. Ethanol is eliminated from the body mainly by oxidative metabolism in the liver by Class I isoenzymes of alcohol dehydrogenase (ADH). Ethanol is an example of a drug for which the Michaelis–Menten pharmacokinetic model applies and the Michaelis constant ( k m) for Class I ADH is at a BAC of 2–10 mg/100 mL. This means that the enzyme is saturated with substrate after the first few drinks and that zero-order kinetics is adequate to describe the declining phase of the BAC profile in most forensic situations (BAC > 20 mg/100 mL). After drinking on an empty stomach, the elimination rate of ethanol from blood falls within the range 10–15 mg/100 mL/h. In non-fasted subjects the rate of elimination tends to be in the range 15–20 mg/100 mL/h. In alcoholics during detoxification, because activity of microsomal enzyme (CYP2E1) is boosted, the ethanol elimination rate might be 25–35 mg/100 mL/h. The slope of the BAC declining phase is slightly steeper in women compared with men, which seems to be related to gender differences in liver weight in relation to lean body mass. The present evidence-based review suggests that the physiological range of ethanol elimination rates from blood is from 10 to 35 mg/100 mL/h. In moderate drinkers 15 mg/100 mL/h remains a good average value for the population, whereas in apprehended drivers 19 mg/100 mL/h is more appropriate, since many of these individuals are binge drinkers or alcoholics. In preparing this article, a large number of peer-reviewed publications were scrutinized. Only those meeting certain standards in experimental design, dose of alcohol and blood-sampling protocol were used. The results presented can hopefully serve as best-practice guidelines when questions arise in criminal and civil litigation about the elimination rate of ethanol from blood in humans.