Barbiturates
Now
largely obsolete as anxiolytic and are mainly used in anesthesia (thiopental)
and epilepsy (phenobarbital)
Taking
BARBs with other CNS depressants can be extremely dangerous and may even lethal
Examples
include: alcohol, tranquillizers, opioids (heroin, morphine, codeine or
methadone), and antihistamines (found in cold, cough, and allergy remedies)
Barbiturate
Mechanism of Action
Enhance GABAnergic Transmission
-increase
opening time of GABAnergic channels both in the presence or absence of GABA
-increase
receptor affinity for GABA
However,
they bind to a different site of the GABA A - receptor / chloride channel. At
high concentrations they may be GABA-mimetic
Barbiturates
are less selective than benzodiazepines, they also:
-depress
actions of excitatory neurotransmitters
-exert
nonsynaptic membrane effects
Disadvantages
of Barbiturates
-increase
toxicity compared to benzodiazepenes
-psychological
dependence
-physiological
tolerance: No tolerance to lethal action of drug
-strongly
induce hepatic CYP450 & conjugating enzymes > increase metabolism of
many other drugs
-flumazenil
not effective
-death
may occur by overdose (often choice to commit suicide)
In
low doses, have a tranquilizing effect. As dose increases, hypnotic or sleep
inducing effect. Even large doses actas anticonvulsants and anesthetics.
Barbiturates has small therapeutic index.
Sedation
> hypnosis > anesthesia > coma > death
Barbiturates
Adverse effects
-excessive
CNS depression
-hypersensitivity
reactions
-excitement
-respiratory
depression and hypotension
-coma
and death in overdose
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