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Physiology & Science: Psychiatry > Anxiolytic Drugs and Hypnotics > Flashcards

Anxiolytic Drugs and Hypnotics Flashcards

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1
Q

What are the differences between anxiolytics and hypnotics?

A
  • Anxiolytics are used to treat anxiety and its psychological and physical symptoms.
  • Hypnotics are used to treat insomnia (anxiety can cause insomnia)
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2
Q

What are the main types of anxiolytics?

A
  • Barbiturates
  • Benzodiazepines + Z drugs
  • 5-HT1A receptor agonists
  • B-adrenoreceptor antagonists
  • Antihistamines
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3
Q

What is the most common configuration for a GABAA receptor?

A
  • 2 alpha
  • 2 beta
  • 1 gamma

standard pentameric structure

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4
Q

What molecule terminates GABA activity at its receptor?

A

GAT transporter -> stimulates uptake of GABA

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5
Q

Where does GABA bind to on the GABAA receptor?

A

On the alpha subunits (GABA agonists or antagonists)

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6
Q

Where do benzodiazepines and barbiturates bind to on the GABAA receptor?

A
  • Benzodiazapine binding site is between two subunits (eg. between gamma and alpha)
  • Barbiturates act as allosteric modulators, bind somewhere inside channel but in extracellular space.
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7
Q

What is meant by allosteric?

A

An allosteric molecule will bind at a site distinct from the agonist binding site. Eg. GABAA has multiple allosteric binding sites.

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8
Q

Barbiturates are positive allosteric modulators. What is their action?

A
  • Bind to allosteric site on GABAa receptor
  • They are positive allosteric modulators
  • Increase time of chloride channel opening
  • Therefore increasing functional response (GABA efficacy)
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9
Q

Barbiturates have other actions at high doses too, so are classed as ‘dirty’ compounds. What are these actions?

A
  • Direct agonists at very high conc at GABAa receptors
  • Glycine receptor (inhibitory) - barbs do same thing here
  • Block nAChR + 5HT3 receptors
  • Block AMPA/Kainate receptors
  • Block Ca2+-dependent NT release

Also have high risk of OD and no antidote for the OD.

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10
Q

What conditions are barbiturates still used in?

A
  • Epilepsy
  • General anaesthesia
  • Euthanasia
  • Capital punishment
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11
Q

Benzodiazepines are also positive allosteric modulators. What is their action in comparison to barbiturates?

A
  • Bind to alpha-gamma interface (- but not to all GABAA receptors)
  • GABA binding site stabilsation, binding sites more readily exposed
  • Increase GABA affinity (so increase binding rather than functional response like barbs)
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12
Q

Why do benzodiazepines not bind to all GABAA receptors?

A
  • There are 6 subtypes of the alpha subunit (a1-a6)
  • Benzos only bind to receptors containing a1,2,3,5
  • This is because they contain a histadine residue in the BZD binding pocket
  • a4,6 contain arginine (so benzos can’t bind)
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13
Q

Name a benzodiazapine antagonist and what is it used for?

A

Rumenazil - a competitive antagonist, used in BZD overdose.

Actually a horrible drug so better to conservatively manage the patient (fluids etc).

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14
Q

Are short-acting benzodiazepines used as hypnotics or anxiolytics?

A

Hypnotics - so they can take it before bed for it to last the night and prevent sedative actions throughout the day.

Eg. Zolpidem, Temazepam, Lorazepam

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15
Q

How do Z-drugs work and how are they similar and different to benzodiazepines?

A
  • Act at benzo site on GABAa receptor
  • Increase affinity
  • They are quite subtly structually different, which means they only act as hypnotics and don’t produce anxiolytic effects.

Eg. Zolpidem

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16
Q

How does barbiturates and benzodiazepine withdrawal result in seizures?

A
  • Symptomatic - more glutamate than GABA activity
    • Barbiturates/BZDs -> more GABA activity
  • In tolerance -> body tries to counteract by adding more glutamate receptors, so more imbalance occurs
  • So need to give even more medication to increase GABA activity to counteract the neuroplasticity taking place
  • If you go cold turkey/take them away, you have even more excitation (seizures) than you had at the beginning so patients need to be carefully titrated off.
17
Q

Why are barbiturates less favoured over Benzodiazepines/Z-drugs?

A
  • Increased chance of overdosing
  • Lack of antidote to overdosing
  • High risk of tolerance induction / addiction
18
Q

Why are benzodiazepines used in alcohol addiction?

A
  • Alcohol increases GABA receptor firing (inc inhibition)
  • Tolerant to alcohol - upregulate glutamate population to balance out
  • Take away alcohol suddenly - too much excitation happening than in original state so seizures can be induced.
  • BZDs can be used to restore status quo and weane the patient off by titrating it to much lower level than alcohol was doing so starts to trick body to get rid of some glutamate receptors.
19
Q

What class of receptors are 5HT receptors and where are they found?

A

Metabotropic (apart from 5-HT3) - ion channels.

Seven families, with at least 14 members.

Found pre and post-synaptically.

20
Q

Which molecule metabolises serotonin and which molecule recaptures it for reuptake?

A

MAO / monoamine oxidase metabolises it.

SERT is the selective reuptake transporter.

21
Q

What are characteristics of 5HT1A?

A
  • Mainly pre-synaptic
  • Auto-inhibitory (so stop further 5HT release)
22
Q

What modalities/functions is 5HT associated with in the brain?

A
  • Mood
  • Sensation
  • Cognition
  • Memory processing
23
Q

What is the most commonly prescribed 5-HT1A agonist?

A

Buspirone - for GAD, low-risk of tolerance induction/withdrawal

24
Q

Where are (a1, a2, b1, b2) adrenoreceptors found synaptically?

A
  • a2 presynaptic
  • a1, b1, b2 postsynaptic
25
Q

How do beta-adrenoreceptor antagonists treat anxiety?

A
  • Eg. propranolol
  • Reduce peripheral symptoms of anxiety (tachycardia, inc BP) by blocking B1 and B2 receptors
  • > decrease HR
  • > block renin release (so decrease BP)
26
Q

How are antihistamines used as hypnotics?

A
  • Peripheral histamine receptors for inflammatory response.
  • Central histamine receptors responsible for arousal and wakefulness
  • Non-drowsy antihistamines don’t cross BBB (hydrophillic), so just treat inflammatory response.
  • Nytol (drowsy) - antihistamine that can cross BBB due to being hydrophobic.
  • Not very strong but available OTC

Physiology & Science: Psychiatry (5 decks)

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