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Y2 Pharmacology and Therapeutics > Opiates/Opioids > Flashcards

Opiates/Opioids Flashcards

1
Q

Give examples of opiates

A

Morphine
Codeine
Thebaine
Papaverine

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2
Q

Describe the hydroxyl structure of morphine

A

2 Altered hydroxyl groups
Hydroxyl group at position 3 = binding site
Hydroxyl group at position 6 = oxidise this OH and lipophilicity increases 10 fold

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3
Q

Describe the nitrogen structure of morphine

A

Tertiary nitrogen
Permits receptor anchoring for the analgesic effect
Affinity is dependent on the tertiary nitrogen

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4
Q

What do changes to the methyl group on nitrogen in morphine cause

A

Extending the side chain to 3+ carbons -> antagonists

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5
Q

Which structural elements are necessary for activity of morphine accord to the morphine rule

A

Aromatic Ring
Basic (tertiary) nitrogen
Quaternary carbon centre
Phenyl group

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6
Q

Describe the pharmacokinetics of opioids (admin and absorption in the gut)

A

IV or oral

Opioids are weak bases and thus are likely to be ionised in the acidic stomach and poorly absorbed
Unionised in the SI - more readily absorbed
First pass metabolism decreases the bioavailability

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7
Q

Describe the ionisation of opioids in the blood

A

Blood pH = 7.4.
Therefore most opioids will be largely ionised in the blood
Usually <20% unionised
This is the component that can access tissues.

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8
Q

Describe the lipid solubility of opioids and its general rule

A

Methadone/Fentanyl&raquo_space; Heroin > Morphine

More lipid soluble, more potent

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9
Q

Describe the metabolism of opioids

A

Morphine – Morphine-6- glucuronide (10% - active metabolite)
Fentanyl - fast metabolism
Methadone - slow metabolism

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10
Q

How do opioids work

A

Action via specific opioid receptors

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11
Q

Give examples of endogenous opioid peptides

A

Endorphins
Enkephalins
Dynorphins/neoendorphins

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12
Q

Which receptors do endorphins bind to and what is the result of this

A

Mu or Delta

Pain/sensorimotor

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13
Q

Which receptors do enkephalins bind to and what is the result of this

A

Delta

Motor/cognitive function

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14
Q

Which receptors do dynorphins bind to and what is the result of this

A

Kappa

Neuroendocrine

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15
Q

Describe the cellular mechanism of action of opiate receptors

A

Depressant
Hyperpolarisation (increase in K+)
Decrease in Ca2+ inward current
Decrease in adenylate cycles activity

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16
Q

What are the effects of opioids

A

Analgesia
Euphoria
Depression of cough centre (anti-tussive)
Depression of respiration (medulla)
Stimulation of chemoreceptor trigger zone (nausea/vomiting)
Pupillary Constriction
G.I. Effects

17
Q

What are the 2 main things that analgesia causes

A

Decrease in pain perception

Increase in pain tolerance

18
Q

Describe the pain perception pathway and its receptors

A
  1. Peripheral tissue
  2. Dorsal horn (mu or kappa receptors) -> spinothalamic tract
  3. Thalamus (mu)
  4. Cortex (mu or delta)
19
Q

Describe the pain tolerance pathway and its receptors

A
  1. +ve effect on PAG from cortex and thalamus (mu or kappa)
  2. +ve effect on NRM from PAG (delta)
  3. +ve effect on NRPG (mu, delta) from the post ganglionic neurone
  4. +ve effect on NRM (delta) form NRPG
  5. -ve effect on dorsal horn from NRM
20
Q

Describe the role of the hypothalamus and LC on the pain pathway

A

Hypothalamus (kappa) - +/- effect on PAG

LC - Sympathetic arm of the brain. Not part of the pain pathway. An activated sympathetic nervous system will suppress painful stimuli

21
Q

substantia gelatinosa?

A

-

22
Q

Where are the sites of opioid action

A

Dorsal horn
PAG
NRPG
Peripheral tissue

23
Q

Explain how opioids induce euphoria

A
  1. Opiates bind to mu receptors on GABAminergic neurones
  2. Reduced GABA release
  3. VTA
  4. NAcc
  5. Dopamine release
24
Q

Describe the neural pathway involved in the cough reflex

A
  1. Stimulation of mechano/chemoreceptors
  2. Afferent impulses to cough centre in medulla
  3. Efferent impulses via parasympathetic and motor nerves to the diaphragm, intercostal muscles and lung
  4. Increased contraction of diaphragmatic, abdominal and intercostal muscles
  5. Noisy expiration / cough
25
Q

Which receptors are involved in the neural pathway involved in the cough reflex

A

ACh/NK C-fibres relay to vagus

5HT1A receptors involved in medullary response

26
Q

How do opioids effect the cough reflex and why

A

They are anti-tussive (inhibitory)
Reduced 5HT1A receptor function in the dorsal raphe nucleus leads to an increase in 5HT levels which may depress discharges from inspiratory motorneurones.
Inhibition of Ach/NK C-fibres relay to vagus

27
Q

Explain how opioids cause respiratory depression

A

Inhibition of the pre-Botzinger complex in the ventrolateral medulla
Inhibition of chemoreceptors that provide tonic drive to resp. motor output (senses pH changes)

28
Q

Explain how opioids cause nausea/vomiting

A

Low doses of opioids activate mu opioid receptors in the chemoreceptor trigger zone (CTZ), thereby stimulating vomiting by activating the medullary vomiting centre

29
Q

Explain how opioids cause miosis

A
  1. Activation of the Optic nerve
  2. Pretectalnnucleus
  3. Edinger-westphal nucleus
  4. Oculomotor nerve
  5. Ciliary ganglion

Opioids bind to mu receptors on the dinger Westphalia nucleus

30
Q

Explain how opioids cause GI disturbance

A

Several opioid receptor types can be demonstrated on myenteric neurons, and both κ- and μ-receptor agonists regulate cholinergic transmission in the myenteric plexus

31
Q

Explain how opioids cause Urticaria

A

non-IgE mediated histamine release

32
Q

Describe opioid tolerance

A

-

33
Q

Describe the symptoms associated with opioid dependence

A

Withdrawal associated with
Psychological craving
Physical withdrawal
(resembling flu)

34
Q

What are the symptoms of an opioid overdose

A

Coma
Respiratory depression
Pin-point pupils
Hypotension

35
Q

What is used to treat an opioid overdose

A

Naloxone (opioid antagonist) i.v.

36
Q

Why may codeine and heroin be considered prodrugs

A

they do not possess the position 3 hydroxyl group, therefore are unable to bind receptors as well as morphine

Their active metabolites are morphine

37
Q

Describe the lipid solubility of codeine

A

More lipid soluble than morphine, but less potent due to metabolism

Y2 Pharmacology and Therapeutics (34 decks)

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