Barbituric acid, the precursor of barbiturates, was first produced
in 1864 by condensation of malonic acid and urea; it had no
central nervous system (CNS) effects. In 1903, diethyl barbituric
acid (barbital) was created as the first barbiturate with
CNS inhibitory effects. Barbiturates were commonly used as
sedative-hypnotics in the mid-twentieth century; meantime
they were abused by some people as sold on the street. Use of
barbiturates quickly dropped after introduction of benzodiazepines
as the safer sedative-hypnotics. However some of the
barbiturates are still used as anticonvulsants and some for
euthanasia.
A white or almost white, crystalline powder, hygroscopic.
Human
Pentobarbital as sodium salt has been used as a sedative and
hypnotic in the short-term management of insomnia. Pentobarbital
sodium has also been used for premedication in
anesthetic procedures. Pentobarbital is FDA-approved for the
emergency control of certain acute convulsive episodes, e.g.,
those associated with status epilepticus, cholera, eclampsia,
meningitis, tetanus, and toxic reactions to strychnine or local
anesthetics. The other indications for pentobarbital include
treatment of nonfatal submersion and traumatic/nontraumatic
raised intracranial pressure.
Animal
Intraperitoneal (IP) injection of pentobarbital is used in
experimental medicine as an anesthetic in small animals such
as rat and mouse. Pentobarbital is an important drug for
relieving convulsive seizures, especially when caused by
strychnine.
Sedative, hypnoyic.
Controlled substance (depressant).
ChEBI: Pentobarbital sodium is an organic molecular entity.
Sodium (9.6 parts) was dissolved in butanol (192 parts) and di-n-butyl ethyl 1-methyl-n-butylmalonate (62.8 parts) and urea (14.4 parts) were added to the warm solution with agitation. The mixture was then heated to reflux temperature in three quarters of an hour and maintained for 2 hours. The reaction mass was kept, water (150 parts) added, the aqueous portion separated, and the butanol layer extracted with water (3 x 50 parts). The combined aqueous extracts were then given 3 small extractions with benzene, the aqueous liquors separated, charcoaled, filtered and precipitated with concentrated hydrochloric acid (acid to congopaper). The solid was collected, washed with water, dissolved in N-sodium hydroxide and reprecipitated with carbon dioxide. On recrystallization, from aqueous alcohol, the pentobarbitone was obtained.
Crystalline granules or white powder. Used as an anesthetic and sedative.
Freely soluble in water. Aqueous solutions are unstable upon storage.
Poison by ingestion,
intraperitoneal, subcutaneous, intravenous,
intraduodenal, intramuscular, intracerebral,
parented, and rectal routes. An
experimental teratogen. Other experimental
reproductive effects. Human systemic
effects by ingestion: wakefulness, change in
motor activity, ataxia, and antipsychotic
effects. Mutation data reported. When
heated to decomposition it emits toxic
fumes of NOx and Na2O.
Routes and Pathways Relevant Physicochemicals Properties
Pentobarbital sodium, with a molecular weight of 248.3,
consists of white, crystalline granules or white powder with
a slight characteristic odor. The melting point equals 130 °C
and respective vapor pressure is 3.02 × 1010 mmHg at 25 °C.
Pentobarbital is very soluble in water (679 mg l1), freely
soluble in alcohol, and practically insoluble in ether. pH of
a 10% solution in water is between 9.8 and 11.0. Its dissociation
constant (pK) and octanol/water partition coefficient (log
Kow) are 7.88 and 2.10, respectively. Henry’s law constant is
8.5 108 Pa m3 mol1 at 25°C.
Environmental Persistency
Due to lack of hydrolyze-prone functional groups, pentobarbital
is not expected to undergo hydrolysis in the environment.
Also, pentobarbital does not contain chromophores to absorb
wavelengths higher than 290 nm and therefore is not susceptible
to direct photolysis by sunlight.
Environmental Degradation
Pentobarbital has been positively identified (not quantified) in
a ground-water sample collected from a well 300 m from
a landfill which received wastes between 1968 and 1969 and
re-sampling 21 years later (in 1991) revealed the presence of
pentobarbital at a concentration of 1 mg l-1 which shows
persistency of pentobarbital in the environment.
