Axiolytics and Sedatives Flashcards
The first class of anxiolytic drugs to be discovered were the —————- and all drugs in this class are notable for having potent sedative effects.
barbiturates
Tachyphylaxis
is a sudden-onset drug tolerance which is not dose dependant and is difficult to reverse.
Receptor sites for both barbiturates and benzodiazepines
are adjacent to but are not the same location as the GABA (gamma-aminobutyric acid) sites on the cell membrane of neurons in the CNS.
What happens to GABA receptors when barbiturate or benzodiazepine binds to it’s specific receptor site?
the GABA receptor site changes in configuration and the affinity of that site for holding on to the GABA neurotransmitter is increased.
GABAa receptors
are ligand-gated ion channels.
ionotropic
GABAb receptors
are G protein-coupled receptors
metabotropic
what is the effect of increased GABA binding affinity?
The increased affinity for GABA at its receptor sites results in more frequent and prolonged opening of the chloride ion channels on the neuron.
how are seizures affected by blocking or promoting GABA binding?
blocking GABA function can result in seizures and augmenting GABA function can afford protection against seizures
Barbiturates
first introduced for medical use in the early 1900s.
Barbiturates have also been used as anticonvulsants and as anesthetic agents.
Barbiturates general MOA
CNS depressants, Barbiturates produce a wide spectrum of central nervous system depression that ranges from mild sedation to coma depending on dose
• Barbiturates do not raise the pain threshold and have no analgesic properties.
They are generally classified as being ultra-short acting, short acting, intermediate acting or long-acting.
Ultra-short acting barbiturates
- The ultra-short acting barbiturates produce anesthesia within about one minute after intravenous administration.
- Ultra-short acting barbiturates in current medical use include:
- Methohexital/ Brevital
- Thiamyl/ Surital
- Thiopental/ Pentothal (induction phase of general anesthesia.)–truth serum!
Short acting barbiturates
- The short acting barbiturates are either taken orally or administered by IV. Oral doses may produce effects within approximately 15 to 30 minutes with a duration of 6 to 8 hours or longer. Short acting barbiturates include:
- Amobarbital/ Amytal
- Pentobarbital/ Nembutal (physician assisted suicide)
- Secobarbital/ Seconal
- Tuinal (Amobarbital/Secobarbital combination)
orally or administered by IV
all Schedule II drugs.
Intermediate-acting barbiturates
- After oral administration, the onset of action is from 20 to 40 minutes and the effects last up to six hours. Intermediate- acting barbiturates include:
- Butalbital/ Fiorinal (migraine med)
- Butabarbital/ Butisol
- Talbutal/ Lotusate
- Probarbital/ Alurate
used for insomnia and pre-operative sedation as well as being added to aspirin or acetaminophen as headache medications.
Long-acting barbiturates
- The full effects of these long-acting barbiturates are generally realized in ~1 hour and may last for ~ 12 hours.
- The long acting barbiturates are now used primarily in the treatment of seizure disorders.
- The long-acting barbiturates include:
- Phenobarbital/ Luminal
- Mephobarbital/ Mebaral
Phenobarbital / Luminal uses
• Phenobarbital is the most widely used anticonvulsant worldwide and the oldest medication for seizure control still commonly used.
• Phenobarbital also has sedative and hypnotic properties but as with other barbiturates, it has been superseded by the benzodiazepines for these indications.

issues with Barbiturates
As anxiolytics and sedatives, barbiturates have largely been replaced because of multiple potential problems which include:
• Drug tolerance
• Psychological and physical dependence
• Severe withdrawal symptoms (which can sometimes be fatal)
• Potential for coma and respiratory failure, particularly when alcohol is consumed.