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Pharmacology > Opioids > Flashcards

Opioids Flashcards

1
Q

What are the important structural features of morphine?

A

Hydroxyl groups on position 3 and 6 - contributes to lipophilicity
Tertiary nitrogen - required for receptor binding

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2
Q

What is the structural difference between heroin and morphine?

A

There is acetylation of the OH groups on position 3 and 6.

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3
Q

What is the structural difference between codeine and morphine?

A

Codeine has a methyl group added to the OH group on C3.

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4
Q

What is the name of the opioid antagonist?

A

Naloxone

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5
Q

What is the pharmacokinetics of opioids and what is the most effective route of administration?

A

Opioids are weak bases pKa >8. Therefore it will be ionised in the stomach and not easily absorbed. In the small intestine it will be unionised and more readily absorbed. There is heavy first pass metabolism in the liver though.
IV as opioids are not very lipid soluble.

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6
Q

What is the order of lipid solubility and therefore potency of the opioids heroin, morphine and fentanyl?

A

Methadone/Fentanyl, Heroin, Morphine

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7
Q

What is the metabolism of morphine?

A

Active metabolite produced is M6G (morphine 6 glucoronide). M6G is a μ-opioid receptor agonist with potent analgesic activity
Action is prolonged due to production of an active metabolite.

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8
Q

What is the difference in metabolism between fentanyl and methadone?

A

Fentanyl is fast metabolism whereas methadone is a slow metabolism. Methadone would be used in treatment of heroin addicts and fentanyl used in a clinical setting.

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9
Q

Describe the metabolism of codeine

A

It is a prodrug of morphine, it is activated in the liver by CYP2D6 (dealkylation) which is slow. It is deactivated faster by CYP3A4.
Only 5-10% of codeine is actually converted into morphine.

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10
Q

What are the endogenous opioid peptides?

A

Endorphins
Enkephalins
Dynorphins/neoendorphins

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11
Q

What type of receptors do endorphins act on, the areas and their effect?

A

μ or δ receptor
Thalamus, Nucleus accumbens, Amygdala, PAG
Pain, Mood, CVS

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12
Q

What type of receptors do enkephalins act on, the areas and their effect?

A

δ receptor
Nucleus accumbens, cerebral cortex, amygdala
Pain, Mood, CVS

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13
Q

What type of receptors do dynorphins act on, the areas and their effect?

A

K receptors
Hypothalamus
Appetite

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14
Q

What is the cellular MOA of opioids?

A

Depressant effects
-Decreased Calcium inward current
-Hyperpolarisation (increased potassium efflux)
-Decreased adenylate cyclase activity (less cAMP)
Increased stimulation is due to decreased GABA stimulation.

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15
Q

What are the pharmacodynamic effects of opioids?

A 
Analgesia
Euphoria
Depression of cough centre (anti-tussive)
\+Depression of respiration
\+Stimulation of CTZ
\+Pupillary constriction
\+GI effects
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16
Q

Describe the pain tolerance mechanism

A

Direct input from the thalamus to the PAG
Stimulatory or inhibitory modulation from the cortex to the PAG (peri-aqueductal grey region)
From the PAG signals sent to NRM (nucleus raphe Magnus)
Independent arm is the NRPG (feedback site for pain tolerance) and sends signals to NRM
NRM sends inhibitory descending signals via dorsal horn to decrease pain sensation

Hypothalamus also modulates PAG
Locus coeruleus, part of SNS, has negative effect on pain sensation.

17
Q

What are the possible target sites of opioids?

A

Periphery (at site of tissue injury)
Dorsal horn
PAG
NRPG

18
Q

How are the euphoric effects of opioids produced?

A

Acts on μ receptor
Inhibit GABA stimulation
Therefore increased firing rate to VTA neurones
More dopamine release in nucleus accumbens

19
Q

What is the normal cough reflex path?

A
  1. Stimulation of chemo-/mechno-receptors, send signal via vagus nerve
  2. Afferent impulses to cough center in the medulla
  3. Efferent impulses to the diaphragm, intercostal muscles and lung
  4. Increased contraction of diaphragm, abdominal muscles and intercostal ribs
20
Q

What are the targets of opioids in the cough mechanism?

A

Inhibits relay of C-fibres to the vagus nerve
Inhibits afferent impulses to cough centre in the medulla
Inhibits activation of 5HT1A receptors which have negative feedback on serotonin

21
Q

How is respiratory depression a problem when taking opioids?

A

It is a problem in high doses
There is disconnect between the central chemoreceptors (sense pC02 in blood) and medullary respiratory centre.
The pre-botzinger complex is also inhibited, this usually drives the ‘respiratory rhythm’.

22
Q

How is nausea and vomiting a problem when taking opioids?

A

Opioids switch off GABA release which usually surpresses the chemotactic trigger zone (CTZ).
Low doses of opioids activate mu opioid receptors in the chemoreceptor trigger zone (CTZ), thereby stimulating vomiting.

23
Q

How does miosis occur when taking opioids?

A

Opioids hijack the activation of PNS, it stops GABA so that the PNS is constantly activated and you get constricted pupils. -> use in diagnosis, in unconsciousness, the pupils are usually slightly dilated

24
Q

What is the effect of opioids on GIT?

A

Acts on κ- and μ receptors which decrease activity of neurones in the myenteric plexus.
Decreased gastric emptying/motility.
Increased water reabsorption

25
Q

Which opioids stimulate histamine release?

A

N-methyl group and 6-OH group is common to those who stimulate non-IgE mediated histamine release

26
Q

How is tissue tolerance achieved when taking opioids?

A

There is upregulation of the molecule arrestin.
Arrestin stimulates receptor internalisation so in chronic opioid use there are less receptors on the cell membrane so the tissue becomes less sensitive.

27
Q

What are the symptoms of opioid dependence?

A 
Psychological craving
Physiological craving (flu-like symptoms); N & V, shakes (up regulation of adenylate cyclase), muscle cramps
28
Q

What are the clues to look out for in opioid overdose?

A 
Coma
Pinpoint pupils
Respiratory depression
Hypotension
Treat with IV Naloxone

Pharmacology (19 decks)

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