Barbiturates bind to the GABAA receptor at the beta subunit, which are binding sites distinct from GABA itself. When the barbiturate has binded to the receptor, the dissociation rate of GABA decreases and the duration of GABA activated opening of chloride channels increases which depresses RAS or the reticular activating system. RAS is a set of connected nuclei in the brains of vertebrates that is responsible for regulating arousal and sleep-wake transitions. When RAS is depressed, wakefulness is then decreased.
Barbiturates are classified as ultra-short, short, intermediate and long acting depending on how quickly they act and their duration of action. Ultra-short acting, such as thiopental, produces unconsciousness within about a minute of intravenous injection and is used to prepare patients for surgery. These drugs are found in hospital settings only and therefore assumed to have a low abuse potential. Longer acting drugs such as Phenobarbital and Mephobarbital are prescribed (rarely) for the treatment of insomnia, and when taken in the day can aid in anxiety and tension. Barbiturates are rarely prescribed any longer for the treatment of insomnia, anxiety, or tension due to their very high risk of physical dependence and fatal overdose. Due to the structural nature of barbiturates the duration of action does not always correlate well with the biological half life
Barbiturates are classified as ultra-short, short, intermediate and long acting depending on how quickly they act and their duration of action. Ultra-short acting, such as thiopental, produces unconsciousness within about a minute of intravenous injection and is used to prepare patients for surgery. These drugs are found in hospital settings only and therefore assumed to have a low abuse potential. Longer acting drugs such as Phenobarbital and Mephobarbital are prescribed (rarely) for the treatment of insomnia, and when taken in the day can aid in anxiety and tension. Barbiturates are rarely prescribed any longer for the treatment of insomnia, anxiety, or tension due to their very high risk of physical dependence and fatal overdose. Due to the structural nature of barbiturates the duration of action does not always correlate well with the biological half life