Detection of a Single Drug Exposure in Hair

Abstract

The influence of drug incorporation on melanin affinity, lipophilicity and membrane permeability is of paramount importance. Despite their high lipophilicity levels, some drugs have quite low incorporation rates into hair, suggesting that the higher incorporation rates of basic drugs (cocaine, amphetamines, etc.) than neutral (steroids, benzodiazepines, cannabinoids, etc.) or acidic drugs are strongly related to the ability of the drug to penetrate the membrane based on the pH gradient between the blood and the acidic hair matrix. When using hair analysis as a matrix during investigative analysis (e.g. in workplace drug testing, doping, driving under the influence and drug-facilitated crime), it is important to know whether the analytical procedure is sensitive enough to identify traces of drugs or even single exposures. The concept of minimal detectable concentration in hair is of interest in order to document negative findings, but limited data are currently available in the scientific literature. Until laboratories have sensitive enough methodologies to detect a single use of a drug, care should be taken when comparing urine and hair findings.