aDaytime sedative and anticonvulsant.
Phenobarbital, USP. Phenobarbital, 5-ethyl-5-phenyl-barbituric acid (Luminal), is a long-acting sedative and hypnotic. It is also a valuable anticonvulsant, especially in generalized tonic-clonic and partial seizures (see the discussion on anticonvulsants). Metabolism to the ^-hydroxylphenyl compound followed by glucuronidation accounts for about 90% of a dose.
BARBITURATES WITH AN INTERMEDIATE DURATION OF ACTION (3-6 HOURS)
Barbiturates with an intermediate duration of action are used principally as sedative-hypnotics. They include amobarbital, USP, 5-ethyl-5-isopentylbarbituric acid (Amytal), and its water-soluble sodium salt, amobarbital sodium, USP, 5-allyl-5-isopropylbarbituric acid (aprobarbital [Alurate]); butabarbital sodium, USP, the water-soluble sodium salt of 5-sec-butyl-5-ethylbarbituric acid (Butisol Sodium).
BARBITURATES WITH A SHORT DURATION OF ACTION (LESS THAN 3 HOURS)
Barbiturates that have substituents in the 5-position promoting more rapid metabolism (e.g., by increasing the lipophilicity) than the intermediate group include pentobar-bital-sodium, USP, sodium 5-ethyl-5-(1-methylbutyl)barbi-turate (Nembutal); secobarbital, USP, 5-allyl-5-(1-methyl-butyl)barbituric acid (Seconal); and the sodium salt sodium secobarbital. Barbiturates with an ultrashort duration of action are discussed under anesthetic agents.
A wide range of chemical structures (e.g., imides, amides, alcohols) can produce sedation and hypnosis resembling those produced by the barbiturates. Despite this apparent structural diversity, the compounds have generally similar structural characteristics and chemical properties: a nonpolar portion and a semipolar portion that can participate in
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