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Cns Pharmacology Flashcards

1
Q

What sites are involved in N/V
Where are they
Receptors at them

A

CTZ - postrema outside bbb, D2, 5HT3
Vomiting centre - dorsolateral reticular formation of brainstem - D2, 5HT3, M3,
Nucleus of tractus solarius (intergrates afferent signals) - H1, NK1

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2
Q

Causes of nausea and vomiting

A

Drug induced
Pregnancy
Radiotherapy
Psychogenic
Vestibular
Motion sickness
Hypotension’s
Migraine
Abdominal pathological
Raise ICP

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3
Q

Categories of antiemetics and examples

A

Anti cholinergic - atropine, hyoscine
Phenothiazines - prochlorpherazine, promethazine
Butyrophenones - droperidol, haloperidol
Antihistamines - cyclizine, buclizine
5HT3 antangonists - ondansetron, granisetron
Cannaboids - nabilone
NK1 antagonist - aprepitant
Peripherally acting - metoclopramide, domperidone
Steroid - dexamethasone
Miscellaneous - betahistine, sedatives, anxiolytics

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4
Q

Example and method of action of anticholinergic antiemetics

A

Atropine, hyoscine
Cross BBB, act on mACh receptors in vomiting centre and in GI tract
Reduce GI tract tone, increase sphincter tone, reduce gastric secretions

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5
Q

When to use anticholinergic antiemetics
Side effects

A

Motion sickness
Opioid induced nausea

Sedation, dry mouth, blurred vision, pupillary dilation, central anticholinergic syndrome

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6
Q

What is central anticholinergic syndrome
Management

A

Muscurinic antagonists cross bbb causing
Excitement
Drownsiness
Ataxia
Coma

An anticholinesterase that can cross the bbb eg physostigmine

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7
Q

Example and method of action of phenothiazine antiemetics

A

Prochlorperazine, premethazine
Antagonise D2 receptors in CTZ
Antagonise M3 receptors much like anticholinergic antiemetics
Antagonise H1 receptors

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8
Q

Main side effect of phenothiazine antiemetics

A

Sedation

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9
Q

Example and method of action of butyrophenone antiemetics

A

Haloperidol, droperidol
D2 antagonist at CTZ

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10
Q

Main side effects of butyrophenone antiemetics

A

Dissociative phenomenon
QT prolongation
Postural hypotension
Extrapyramidal effects
Neuroleptic malignant syndrome
Hyperprolacinaemia and gynaecomastia

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11
Q

Other effects of haloperidol that aren’t antiemetics

A

Antipsychotic
Anticonvulsant

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12
Q

Why does haloperidol cause postural hypotension

A

Alpha 1 adrenoreceptor block

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13
Q

Example and method of action of antihistamine antiemetics

A

Cyclizine, cinnarizine
H1 antagonism at CTZ

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14
Q

Best type of nausea and vomiting effected by antihistamines

A

Motion sickness

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15
Q

Side effects of cyclizine
Why

A

Dry mouth, tachycardia
Anti muscurinic properties

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16
Q

How do 5HT3 receptor antagonists work for antiemetics, examples

A

Ondansetron tropisetron
Antagonism of 5HT at posteraema, nucleus tractus solitarius, vagus nerve and gi tract

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17
Q

Side effects of ondansetron

A

Headaches
Constipation
QTc prolongation

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18
Q

How do cannabinoids work for antiemetics, examples

A

Antagonism of cannabinoid receptor at CTZ

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19
Q

When are cannabinoids most useful for nausea and vomiting

A

Opioids, cytotoxic chemotherapy and radiotherapy

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20
Q

Side effects of a cannabinoids

A

Hallucinations
Psychosis
Dizziness
Dry mouth

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21
Q

How do neurokinin receptor antagonists work for antiemetics, examples

A

Aprepitant
Act at nucleus of tractus solitarius and dorsal motor nucleus of vagus nerve

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22
Q

Comparison of aprepitant to ondansetron
Half life
Presentation

A

Broader spectrum of activity
11 hours
Oral capsule - prodrug fosaprepitant is available IV

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23
Q

How does dex work as an antiemetic

A

Maybe prostaglandin inhibition
Maybe inhibition of gut or neuronal 5Ht release

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24
Q

What is in a ml vial of dexamethasone

A

3.3mg dex
Sodium
Phosphate
Overall contains between 4mg dex phosphate or 4.3mg dex sodium phosphate

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25
Examples of peripherally acting antiemetic drugs and how they work
Domperidone, metoclopramide D2 antagonism at CTZ, inhibits emetic effects of gastric irritants Antagonises H1 and 5HT Promotes gastric emptying
26
Why do we tend to give metoclopramide not domperidone
Can’t be given paraetnrally Causes qt prolongation, arrhythmia, sudden death has been reported
27
When are metoclopramide particularly useful
Cytotoxic and radiotherapy n and v Impaired gastric transit eg diabetes
28
Bioavailability of cyclizine
80%
29
Side effects of dexamthasone
Increased post op infection and bleeding in the vulnerable Increased convulsions and increased ICP
30
How is cyclizine metabolised
To norcyclizine
31
How is dex metabolised
Hepatic
32
Protein binding of metoclopramide
18%
33
Elimination of metoclopramide
80% in urine - either unchanged or conjugated
34
Side effects metoclopramide
Drowsiness, dizziness, extrapyramidal
35
Oral bioavailability of ondansetron
60%
36
Metabolism of ondansetron
Hepatic Main metaboilte 8-hydroxyondansetron Excreted in urine
37
Medications for status epilepticus
First line benzos Second line - phenytoin, phenobarbital, chlormethazole, paraldehyde
38
Agent of choice for petimal seizure
Ethosuximide Valproate
39
Agent of choice for tonic clinic seizures
Carbamazepine Lamotrigine Phenytoin Valproate Phenobarbital
40
Agents of choice for myoclonus seizure
Valproate Clonazepam Lamotrigine Ethosuximide
41
Agents of choice for atypical seizures
Clonazepam Ethosuximide Lamotrigine Phenobarbital Phenytoin Valproate
42
Risks of antiepileptic medications in pregnancy Mitigation stratergies
Teratogenic Neural tube deficits Coagulation disorders in newborn Incompliance with meds causing seizure! Coucelling and antenatal screening Folate supplementation Pre delivery Vit k
43
How do benzos work in epilepsy
Attach to gaba increasing activity
44
How do barbiturates work in epilepsy
Binds to gaba and facilitates chloride conduction - similar to benzos but different site
45
What class of drug is phenytoin How does it work
A hydantoin Fast sodium channels responsible for depolarisation during APs Bins when refractory so is use dependant
46
Side effects of phenytoin
Hirsuitism Gum hyperplasia Megaloblastic anaemia Fetal malformations
47
Why does phenytoin interact with so many other drugs
85% protein binding - complete with aspirin, phenylbutazone, valproate Enzyme induction - steroids, coumarins, oestrogens, phenobarbitol
48
What is special about phenytoin metabolism
Zero order kinetics - enzyme pathway very rapidly saturated, so half life increases with dose.
49
How does carbamazepine work
Use dependant voltage gated sodium channel blockade Agonist at postsynaptic gaba receptor
50
What is special about carbamazepine metabolism
Half life drops from 30-15hrs due to enzyme induction
51
What is gabapentin How does it work
An amino acid! Competes with amino acids for specific transmembrane transporters Increases concentration and synthesis of gaba Binds to voltage sensitive ca channels Reduces release of na, dopamine and 5Ht Inhibits voltage sensitive na channels Increases 5Ht Prevents neuronal death by inhibition of glutamate synthesis
52
How does valproate work Main uses
Inhibits gaba transaminase increasing gaba levels Peti mal, myoclonus epilepsy, infantile spasm
53
Main issues with valproate
Neural tube deficits Platelet number decrease
54
How does lamotrigine work Main uses
Stabilises inactive presynaptic sodium channels reducing neurotransmitter release Partial seizures, tonic clinic seizures and myoclonic seizures
55
How does levetiracetam work
Thought to bind selectively on epleptigenic neuronal tissue
56
How does vigabactrin work Issues
Inhibits gaba transaminase Causes visual field deficit in 1/3rd of patients Behavioural problems
57
Classes and Examples of tricyclic antidepressants.
Dibenzazepines - clomiparamine, imipramine Dibenzocycloheptanes - amitryptyline, nortriptyline
58
How do TCAs work
Prevent reuptake of neurotransmitters, primerally noradrenaline, but also serotonin and dopamine Acts on presynaptic alpha 2 receptors to increase neurotransmitter release Antagonise mACh, H1, and alpha1 receptors
59
Side effects of TCAs
Sedation Weakness Fatigue Postural hypotension Sinus tachycardia PR and QT prolongation
60
Protein binding of TCAs
95% to albumin
61
Tca metabolism
Hepatic microsomal enzymes N demethylation Ring hydroxylation
62
Classification and examples of MAOIs
Cyclopropylamines - transcypromine Hydrazines - iproniazid, phenelzine Propargylamines - pargyline, selegiline
63
What is the distinction between mao-a and mao-b?
A is more effective at oxidising na and 5Ht Equally effective at metabolising dopamine and tyramine
64
How do MAOIs confir antidepressant effect
Inhibition of mao-a
65
What sort of inhibition do MAOIs confir
Irreversible
66
What do the different MAOIs inhibit
Phenelzine, transcypromine and iproniazid inhibit both isoenzymes non selectively Clorygyline is selective to mao-a Selegiline is selective to mao-b
67
How does selegiline work
Mao-b inhibition thus not antidepressant but raises dopamine levels
68
How long does it take MAOIs to work
Action immediately but no sign of antidepressant action for a few weeks
69
Issues with MAOIs
Unable to metabolise exogenous amines properly thus get pressor effects from tyramine (found in cheese, red wine, marmite) and indirect sympathomimetic drugs including cough medicines. Interaction with pethadine can cause coma
70
What is the only reversible MAOI What does it do Advantage
Moclobemide Reversibley inhibits mao-a Can stop to reverese without haveing to await new mao enzyme formation
71
Common side effects of ssris
Diarrhoea Nausea vomiting Headaches Restlessness Anxiety Withdrawal
72
How long between Ssri and maoi
MAOI 2-5 weeks post stopping ssri Ssri 2 weeks after stopping MAOI
73
Example of Snri
Venlafaxine
74
Example of a selective noradrenaline reuptake inhibitor
Reboxetine
75
What is mirtazapine Effects
A noradrenergic and specific serotonergic antidepressant Increases na and 5Ht Blockades alpha 2 adrenoreceptors
76
Why does lithium accumulate intracellular Effect of this
It is 1A on the periodic table with atomic number 3 and molecular weight 7 Mimics sodium but smaller so can pass through fast sodium channels into cells but not out through the NaKATPase Displaces potassium reducing outward leakage of potassium reducing transmembrane potential (more positive) facilitating depolarisation
77
Target lithium plasma levels
0.4 to 1.0
78
Lithium half life Implication for anaesthesia
12 hours Should be stopped 2-3 days before using a muscle relaxant Especially non-depolarising muscle relaxants which are potentiated. May delay onset and prolong relaxation of sux.
79
Effect of lithium on vasopressin p
Inhibits activity in the kidneys
80
Other hormones effected by lithium
Increases aldosterone secretion Inhibits thyroid hormone release
81
Neurological effects of lithium
Thirst, tremor, muscle weakness, confusion, seizures
82
Side effects of antipsychotics
Extrapyramidal side effects (facial grimace, incoluntary movement, oculogyric crisis, torsion, spams, Parkinsonism, tardive dyskinesia) Increased prolactin secretion Antimuscarinic (dry mouth, constipation, urinary retention, blurred vision Alpha adrenergic - postural hypotension Antihistaminergic - sedation Qt prolongation Agranulocytosis (clozapine)
83
Mechanisms of drugs for Parkinson’s, example
Increase dopamine synthesis - levodopa Decreased peripheral conversions of levodopa - carbidopa Decreased dopamine breakdown - selegiline Dopamine receptor agonists - bromocriptine Dopamine receptor facilitators - amantadine ACh antagonists - benztropine
84
How does levodopa work in Parkinson’s
Racemic dopa has many side effects without being useful, Dopamine can’t cross bbb Give levodopa, we’ll absorbed orally, crosses bbb and converted to dopamine which has effect.
85
What does carbidopa do in Parkinson’s
Give with levodopa Inhibits peripheral conversion of levodopa to dopamine so less systemic side effects and more enters brain.
86
What does domperidone do in Parkinson’s
Dopamine anatagoinst that only slowly crosses bbb so reduces peripheral side effects of dopamine thus permitting use of larger doses than would otherwise be tolerated.
87
How does selegiline work in parkinsons
Selective maob inhibitor Decreases dopamine breakdown
88
Examples and effects of dopaminergic drugs in Parkinson’s Side effects
Bromocriptine, cabergoline Stimulate central d2 receptors Used when levodopa ineffective Side effects of prolactin inhibition, ergot derived so retroperitonal, cardiac and pulmonary fibrosis
89
Use of amantidine in Parkinson’s
Possible facilitation of dopamine release and inhbition of metabolism
90
Use of ach antagonists in Parkinson’s Examples
Benhexol, procyclidine Cross bbb Restore imbalance between cholinergic and dopimanergic effects in brain Antagonise pre synaptic inhibition of dopamine release

Primary Pharmacology (18 decks)

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