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E-lfh FRCA Primary: Pharmacology - Analgesics > Opioid Drugs: General Properties and Mechanisms of Action > Flashcards

Opioid Drugs: General Properties and Mechanisms of Action Flashcards

1
Q

Regarding endogenous opioids (true or false):

The endogenous opioids are steroids

A

False. They are peptides derived from precursor proteins.

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2
Q

Regarding endogenous opioids (true or false):

B-endorphin and ACTH are both derived from the same precursor, pro-opiomelanocortin

A

True

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3
Q

Regarding endogenous opioids (true or false):

The enkephalins are predominantly kappa receptor agonists

A

False. Enkephalins bind primarily to the mu and delta receptor. The dynorphins bind primarily to the kappa receptor.

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4
Q

Regarding endogenous opioids (true or false):

The dynorphins are involved in appetite regulation and control of the circadian rhythm

A

True

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5
Q

Regarding endogenous opioids (true or false):

Endorphins are present at high concentrations in the pituitary and hypothalamus

A

True

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6
Q

What type of receptors are all opioid receptors?

A

The G proteins linked to the opioid receptors are of the Gi/o type:

-There is inhibition of adenylyl cyclase activity reducing cyclic adenosine monophosphate (cAMP) formation
-There is reduced opening of voltage-gated calcium channels reducing presynaptic neurotransmitter release
-There is increased potassium efflux resulting in hyperpolarisation of the cell

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7
Q

Regarding opioid receptors (true or false):

Opioid receptors are ligand-gated ion channels

A

False. They are G protein coupled receptors (GPCRs).

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8
Q

Regarding opioid receptors (true or false):

Activation of opioid receptors leads to closure of voltage-gated calcium channels

A

True

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9
Q

Regarding opioid receptors (true or false):

Activation of opioid receptors results in potassium efflux and hyperpolarisation

A

True. The Ga subunit inhibits adenylyl cyclase; the By dimer is responsible for increasing potassium conductance and closing voltage-gated calcium channels.

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10
Q

Regarding opioid receptors (true or false):

There is increased production of cyclic adenosine monophosphate (cAMP) production due to activation of adenylyl cyclase

A

False. Opioids receptors are Gi/o GPCRs.

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11
Q

Regarding opioid receptors (true or false):

Naloxone is an antagonist at all mu, delta and kappa receptors

A

True

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12
Q

Are opioids weak acids or bases?

A

Weak bases

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13
Q

Why does alfentanil have a more rapid onset of action compared to fentanyl, despite being less potent?

A

The pKa of alfentanil is one pH unit below plasma pH, so it is 90% unionised; fentanyl has a pKa of one pH unit above plasma pH, so only 9% is unionised. This is a 10-fold difference and, since alfentanil is less potent, a higher dose of drug is needed. This creates a very large concentration gradient for the unionised drug to cross the blood-brain barrier.

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14
Q

What are the pKas of morphine, fentanyl, alfentanil and remifentanil?

A

Morphine 8.0
Fentanyl 8.4
Alfentanil 6.5
Remifentanil 7.1

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15
Q

What percentage of morphine, fentanyl, alfentanil and remifentanil is unionised at biological pH?

A

Morphine 23%
Fentanyl 9%
Alfentanil 90%
Remifentanil 68%

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16
Q

What percentage of morphine, fentanyl, alfentanil and remifentanil is bound to proteins in the plasma?

A

Morphine 30%
Fentanyl 84%
Alfentanil 90%
Remifentanil 70%

17
Q

What are the terminal half lives of morphine, fentanyl, alfentanil and remifentanil?

A

Morphine 3 hours
Fentanyl 3.5 hours
Alfentanil 1.6 hours
Remifentanil 3.5 minutes!

18
Q

What are the clearance rates of morphine, fentanyl, alfentanil and remifentanil?

A

Morphine 15-30 ml/min/kg
Fentanyl 0.8-1.0 ml/min/kg
Alfentanil 409 ml/min/kg
Remifentanil 30-40ml/min/kg

19
Q

What is the volume of distribution of morphine, fentanyl, alfentanil and remifentanil?

A

Morphine 3-5 L/kg
Fentanyl 3-5 L/kg
Alfentanil 0.4-1.0 L/kg (so much lower than fentanyl due to its lower lipid solubility)
Remifentanil 0.2-0.3 L/kg

20
Q

What is the relative lipid solubility of fentanyl compared with morphine?

A

Fentanyl is 580 times more soluble than morphine

21
Q

What determines the clinical onset time of most drugs used in anaesthetics including opioids?

A

Ability of the drug to cross the BBB. Therefore, the amount of unbound drug that is unionised at biological pH (dictated by pKa) and the drugs lipid solubility.

22
Q

What is the oral bioavailability of morphine?

A

About 25%

23
Q

Which of the following can be considered as opiates:

A. Fentanyl
B. Codeine
C. Remifentanil
D. Oxycodone
E. Morphine

A

Morphine, Codeine and Thebaine are examples of opiates. The term opiate refers to all naturally occurring drugs derived from opium.

24
Q

Regarding opioids (true or false):

They act via G protein-coupled receptors to open voltage-gated calcium channels, increase potassium efflux and reduce production of cAMP

A

False. Opioids do act through G protein-coupled receptors to close voltage-gated calcium channels, increase potassium efflux and reduce production of cAMP.

25
Q

Regarding opioids (true or false):

Partial agonists are capable of producing the full effect when bound to a receptor

A

False. Partial agonists such as buprenorphine produce sub-maximal effect when bound to the receptor.

26
Q

Regarding opioids (true or false):

Naloxone is an example of a drug which binds to the receptor and has no intrinsic activity

A

True

27
Q

Regarding opioids (true or false):

Opioid receptors are found only in the central nervous system

A

False. Opioid receptors can be found in the GI tract and peripheral tissue.

28
Q

Regarding opioids (true or false):

Pentazocine is an example of an agonist/antagonist which antagonises the action of morphine at mu receptors

A

True

29
Q

Unwanted side effects of opioids include (true or false):

Chest wall rigidity

A

True, especially remifentanil

30
Q

Unwanted side effects of opioids include (true or false):

Reduction in ACTH and ADH release

A

False. Secretion of ACTH, prolactin and gonadotrophic hormone is inhibited and increased secretion of ADH.

31
Q

Unwanted side effects of opioids include (true or false):

Tachycardia

A

False. Actually, a side-effect can be mild bradycardia.

32
Q

Unwanted side effects of opioids include (true or false):

Diarrhoea

A

False. It can actually cause the opposite of this, constipation.

33
Q

Unwanted side effects of opioids include (true or false):

Urinary retention

A

True

E-lfh FRCA Primary: Pharmacology - Analgesics (6 decks)

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