Opioids Flashcards

0
Q

What does the word ‘narcotic’ mean?

A
  • stupor (state of near unconscious) including painkiller
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1
Q

What does the word ‘analgesic’ mean?

A
  • painkiller, drug used to relieve pain
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2
Q

What does the word ‘opiate’ mean?

A
  • DRUGS derived from the juice of the opium poppy
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3
Q

What does the word ‘opioid’ mean?

A
  • drugs (includes opiates) that act at the opioid receptors

- it usually means synthetic whereas opiate refers to natural substances

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4
Q

How is pain transmitted from receptors to higher centres?

A
  • via spinothalamic tract
  • first order neurones receptors for noxious stimuli cell bodies are found in dorsal root ganglion
  • fibres= A delta myelinated and faster conducting; C fibres is unmyelinated
  • terminates in the dorsal horn of spinal cord
  • second order neurones: ascends in contralateral Spinothalamic tract and terminates in the thalamus
  • third order neurones: terminate in the post-central gyrus of the cerebral cortex
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5
Q

How is pain being modulated in the descending pathway?

A
  • Descending fibres from the higher centres eg. periaqueductal grey matter can inhibit transmission in substantia gelatinosa
  • there are different types of fibres involved: enkephalinergic fibres, noradrenergic fibres, serotonergic fibres and local release of dynorphin

->this descending pain modulation is activated by opioids

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6
Q

What are the three families of endogenous opioid peptides?

A
  • dynorphins, enkephalins and endorphins
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7
Q

Morphine

A
  • first alkaline to be extracted from opium

- name after the Greek god of dreams because it causes tendency to sleep

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8
Q

Opioid Receptors

A
  • there are different subclasses: mu opioid receptor (MOP); kappa opioid receptor (KOP); delta opioid receptor (DOP)
  • they can all be antagonised by naloxone
  • another type is Nocieptin receptor (NOP)
  • cannot be antagonised by naloxone
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9
Q

Mu opioid receptor (MOP)

A
  • it is a G-protein coupled receptor which has 7 transmembrane domains
  • this is a crucial receptor in order to respond to morphine
  • mechanism: morphine binds and causes voltage sensitive calcium channels to close; increased potassium efflux and hyperpolarisation; inhibit adenylate cyclase and reduce cAMP
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10
Q

What are the full mu opioid receptor agonists?

A
  • morphine, diamorphine(heroine), codeine, fentanyl(fentanil), methadone
  • heroine could be used for acute left ventricular failure-> reduces preload and anxiety
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11
Q

What are the examples of partial agonists for MOP?

A
  • buprenorphine

- has agonist activity (partially) but will antagonise full agonists and cause withdrawal in opioid dependence

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12
Q

What are the examples for MOP antagonists?

A
  • Naloxone, important use for opioid overdose
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13
Q

What are the routes of opioid administration? (6)

A
  • intranasal-> for dimorphine, usually for children
  • intramuscular
  • transdermal
  • orally
  • intravenous
  • epidural space
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14
Q

What are the main problems with administrating opioids orally?

A
  • poorly absorbed and high first pass metabolism by gut wall and liver
  • oral bioavailiablity 20%
  • oromorph is used for cancer pain and it contains morphine sulphate
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15
Q

What are the actions of morphine?

A
  • CNS: analgesia, euphoria (increase sense of well-being), sedation/ drowsiness/coma, cough suppression, nausea and vomiting, miosis(stimulation of Edinger-westphal nucleus of CN 3)
  • CVS: depression of vasomotor centre at higher doses and mast cell degranulation so results in hypotension
  • Respiratory: respiratory depression and alveolar hypoventilation = respiratory acidosis
  • GI: reduced motility and secretions so result in constipation, spasm of sphincter of Oddi
  • GU: urinary retention
16
Q

What are the problems with long term morphine use?

A
  • tolerance ( ie reduce responsiveness to the drug and requiring higher doses to achieve the same effect) and dependence ( sudden termination of drug can induce a withdrawal effect) can develop.
  • DOP seems to be responsible in causing the withdrawal effect
17
Q

How is morphine being eliminated?

A
  • conjugated with glucoronic acid to morphine-3-glucoronide that is excreted in urine
  • need to adjust dosage with patients with hepatic or renal impairment.
  • liver usually makes the drugs which are more water soluble for kidneys to excrete
18
Q

Coedine

A
  • a prodrug which can be metabolised to the active form (morphine and other metabolites)
  • 1 in 10 people lack CY2D6 enzyme in liver so cannot metabolite coedine into morphine. This means there’s a less analgesic effect
  • often used in combination with other analgesic eg. co-codamol
  • loperamide (related drug) is used in the treatment of severe diarrhoea
19
Q

Fentanyl (Fentanil)

A
  • synthetic
  • 80-100 times more potent than morphine
  • given IV so can have a rapid onset of analgesic effect but short duration
  • used for intra and post operative pain treatment
  • dose in micrograms
20
Q

Methadone

A
  • slow metabolism and fat soluble= long acting
  • maintenance therapy for patients with opioid addictions
  • can block the euphoria effect if IV heroin is used
21
Q

Naloxone (Narcan)

A
  • usually for IV or intramuscular
  • can reverse opioid overdose within 1-2 mins
  • last for 20-30 mins, while half life of morphine is 2-3 hours so continuous infusion of naloxone is required until morphine wears off