A very large group of drugs classified as
hypnosedatives. Of the over 2,500 barbiturates that have been catalogued,
roughly 15 are currently used, in a variety of conditions, including (most
commonly) as an aid for sleeping, as an anesthetic, and in the symptomatic
treatment of epilepsy. Generally, barbiturates depress the activity of all
excitable cells. Barbiturates can be divided into three classes, depending on
speed and duration of action. The long-acting include phenobarbital and
mephobarbital. These produce their effects slowly (approximately one hour after
ingestion) and last roughly 8-12 hours. The intermediate-acting (15-30 minute
onset time; 3-5 hour action) include pentobarbital, secobarbital and amobarbital.
The ultra-short-acting (1-2 seconds; 15-30 minutes) include thiopental and
methohexital. Those in this last group are used primarily as anesthetics and
administration is usually intravenous. With long-term use all the barbiturates
produce tolerance as well as both psychological and physiological drug
dependence.
