Cyclopentobarbital (5)-HRP

Barbiturates are a class of around 12 compounds derivatised from barbituric acid. They are central nervous system (CNS) depressants and can be used as sedatives, hypnotics, anaesthetics and anti-epileptic drugs. Barbiturates can be divided into three main groups according to their duration of action. The ultra-short-acting barbiturates are used clinically as anaesthetics whilst the long-acting barbiturates have anti-convulsant properties. The short-acting compounds are typically used as hypnotics(1, 2). The short-acting barbiturates are extensively metabolised by the liver to more pharmacologically inactive hydroxylated compounds. Only a small proportion of parent compound (<0.2%) appears in the urine collected after 24 hours. However, with large doses, there is usually sufficient of the parent compound present to give an adequate response and some of the hydroxylated metabolites will also cross-react in immunoassays(1).