Scientists agree that alcohol levels in blood or breath are the best way to measure how alcohol is affecting someone's ability to drive. To use and understand chemical tests for alcohol in traffic law enforcement and research on alcohol's impact on driving, it's important to know about the bodily and chemical factors that affect alcohol levels. Understanding the physiological and pharmacological factors that influence these alcohol concentrations is essential for the correct use and interpretation of chemical tests for alcohol. It is also important to recognize the complexity of the relationships between alcohol dosage, time, and pharmacological effects in both research and public education.
Most of the factors and considerations that affect the alcohol content of various body tissues and fluids and the relationships between dosage, time, and effect fall under the umbrella of pharmacokinetics, which involves the absorption, distribution, metabolism, and excretion of drugs. The relationship between alcohol concentrations in different body fluids and tissues, such as the blood-breath ratio of alcohol, is a complex and important factor in alcohol determination. In addition, when using chemical tests for alcohol in traffic law enforcement, a significant amount of time may pass between a significant event (e.g. a crash or alleged violation) and sample collection, resulting in a significant difference in the respective alcohol concentrations of blood or other specimens. As a result, the relationships between alcohol ingestion, distribution, storage, and elimination are critical for highway safety and the evidentiary use of chemical test results.
Pharmacokinetic parameters affect the validity and usefulness of alcohol determinations as indicators of driver impairment in several ways, such as the choice of sample materials and the probative value and interpretation of alcohol analysis results. A thorough understanding of alcohol pharmacokinetics is also necessary for the proper evaluation and assessment of the validity and significance of studies that examine the relationship between alcohol concentrations in body fluids and driver performance or impairment, as well as for understanding the differences between studies.
Several of these issues have become particularly significant with the widespread adoption of per se drinking-driving laws, also known as absolute or blood alcohol concentration offense laws. Alcohol concentrations in body fluids are a key element of these offenses and often serve as the primary evidence regardless of driver impairment. In these cases, the accuracy of alcohol analysis and the validity of blood or breath alcohol concentrations at the relevant time are of paramount importance, as they carry much greater weight than in the traditional use of alcohol analysis results to establish the presence of alcohol at a level consistent with observed driver impairment or to explain a crash or moving violation, or to establish a rebuttable presumption of the influence of alcohol to an unacceptable level.
Alcohol is unusual among drugs in several aspects of its pharmacokinetics. Of particular note are the significant intersubject variations in alcohol tolerance and elimination, the pattern of short-term fluctuations in blood and breath alcohol concentrations, and the partitioning of alcohol between blood and other body fluids and tissues at equilibrium. It is also noteworthy that alcohol is absorbed and distributed in its unaltered state and is not bound to proteins or complexed with other transport systems.
There are many factors that can impact the amount of alcohol in the body, such as the amount consumed, the rate of consumption, body size and weight, and the presence of food. These factors can make it difficult to predict exactly how alcohol will affect an individual, making it important to be cautious when drinking and driving.