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pharmacology > opioids > Flashcards

opioids Flashcards

1
Q

What is the main challenge with the oral administration of morphine?

A

First-pass metabolism by the liver reduces bioavailability by 50%.

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2
Q

How does the dose of oral morphine compare to parenteral administration?

A

10mg oral morphine is equivalent to 5mg subcutaneous (s/c), intramuscular (IM), or intravenous (IV) morphine.

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3
Q

What is the typical duration of action for a single dose of morphine?

A

About 3–4 hours.

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4
Q

What is the purpose of slow-release morphine preparations?

A

Used for palliative care, e.g., MST Continus, taken twice a day.

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5
Q

What should you remember when prescribing oral versus parenteral morphine?

A

Separate prescriptions are needed due to differences in bioavailability.

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6
Q

What are the parenteral routes of drug administration?

A

Subcutaneous (s/c), Intramuscular (IM), and Intravenous (IV).

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7
Q

Which parenteral route is the fastest for drug administration?

A

Intravenous (IV).

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8
Q

What is IV PCA, and why is it used?

A

IV PCA stands for Intravenous Patient-Controlled Analgesia, allowing patients to control their pain relief.

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9
Q

What is the purpose of epidural/CSF administration?

A

To deliver drugs directly into the cerebrospinal fluid for targeted pain relief or anaesthesia.

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10
Q

What is a common example of a transdermal patch, and what is its advantage?

A

Fentanyl; it delivers lipid-soluble drugs over a prolonged period through the skin.

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11
Q

What system do opioids use to relieve pain?

A

The existing pain modulation system in the body.

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12
Q

What are natural opioids in the body called?

A

Endorphins (endogenous morphine) and enkephalins.

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13
Q

What type of receptors do opioids act on?

A

G protein-coupled receptors, using second messengers.

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14
Q

How do opioids affect pain transmitters?

A

They inhibit the release of pain transmitters in the spinal cord and midbrain.

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15
Q

How do opioids modulate pain perception?

A

By changing the emotional perception of pain and inducing euphoria in higher brain centres.

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16
Q

What process do opioids use to inhibit pain?

A

Descending inhibition of pain.

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17
Q

What natural response is linked to opioid action?

A

Part of the fight-or-flight response.

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18
Q

Why are opioids not suited for sustained activation?

A

They were never designed for prolonged use, and sustained activation can lead to tolerance and addiction.

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19
Q

What does potency refer to in pharmacology?

A

Potency describes how well a drug binds to its receptor, relating to its binding affinity.

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20
Q

What does efficacy refer to in pharmacology?

A

Efficacy is the ability of a drug to produce a maximal response, even if all receptor sites are occupied.

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21
Q

What is the difference between full and partial agonists?

A

Full agonists achieve maximum efficacy, while partial agonists produce a limited response even at full receptor occupancy.

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22
Q

What are the relative potencies of diamorphine, morphine, and pethidine?

A

Diamorphine: 5 mg
Morphine: 10 mg
Pethidine: 100 mg

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23
Q

What effect does naloxone have on the dose-response curve of morphine?

A

Naloxone shifts the morphine dose-response curve to the right, indicating competitive antagonism at opioid receptors. Increasing naloxone levels requires higher doses of morphine to achieve the same effect.

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24
Q

What is tolerance in the context of opioid use?

A

Tolerance is the down-regulation of opioid receptors with prolonged use, requiring higher doses to achieve the same effect.

25
Q

What are the two types of dependence caused by opioids?

A

Psychological dependence – craving and euphoria.
Physical dependence – physical reliance on the drug.

26
Q

When does opioid withdrawal start, and how long does it last?

A

Withdrawal starts within 24 hours and lasts about 72 hours.

27
Q

Where else do opioid receptors exist outside the pain system?

A

In the digestive tract and respiratory control centre.

28
Q

How are opioids commonly delivered?

A

Mostly systemically, but sometimes epidurally.

29
Q

What are common side effects of opioids?

A
30
Q

How should opioid dosing be adjusted for different patients?

A

Start with a small dose and titrate up as necessary, as sensitivity varies.

31
Q

What is the first step in managing opioid-induced respiratory depression?

A

Call for help and follow the ABC (Airway, Breathing, Circulation) protocol.

32
Q

What is the antidote for opioid-induced respiratory depression?

A

Naloxone.

33
Q

What is the fastest route for administering naloxone?

A

Intravenous (IV).

34
Q

How should naloxone be administered?

A

Titrate to effect—don’t administer the entire dose at once.

35
Q

Why must naloxone administration be closely monitored in A&E for overdoses?

A

It has a short half-life, so repeated doses may be needed.

36
Q

What is the concentration of naloxone used for treating respiratory depression?

A

400 micrograms per ml.

37
Q

How should naloxone be prepared for administration?

A

Dilute 1 ml of naloxone in 10 ml of saline.

38
Q

How should naloxone be administered for respiratory depression?

A

Titrate to effect, gradually increasing the dose as needed.

39
Q

What is an important consideration when using naloxone ampoules?

A

One ampoule is usually sufficient for an adult dose. If more is needed, consult a colleague before opening additional ampoules.

40
Q

How quickly do opioids lose effectiveness for non-cancer pain?

A

Within weeks.

41
Q

What did a large study reveal about long-term opioid use?

A

50% of patients on opioids for non-cancer pain at 12 weeks were still on them 5 years later.

42
Q

Why is it difficult to stop opioid use in patients?

A

Addiction can lead to manipulative behaviour, making it hard to get patients off opioids.

43
Q

What should be discussed with patients before prescribing opioids for chronic, non-cancer pain?

A

The risks and features of tolerance, dependence, and addiction, and the importance of using short-term courses.

44
Q

What should be agreed upon when starting opioid treatment?

A

A treatment strategy and a plan for ending treatment.

45
Q

What changes have been made to opioid drug labels and packaging?

A

Warnings have been added to support patient awareness of risks.

46
Q

How should opioid dosage be managed at the end of treatment?

A

Taper the dosage slowly to reduce the risk of withdrawal effects, which may take weeks.

47
Q

What is codeine, and how does it work?

A

Codeine is a prodrug that needs to be metabolised by cytochrome CYP2D6 into morphine to be effective.

48
Q

What percentage of the Caucasian population has reduced CYP2D6 activity?

A

10-15%.

49
Q

What happens if CYP2D6 is absent, and what percentage of the Caucasian population is affected?

A

Codeine will have a reduced or absent effect; CYP2D6 is absent in a further 10% of this population.

50
Q

What is the risk in individuals with overactive CYP2D6, and how common is this?

A

5% of this population may be at an increased risk of respiratory depression with codeine. Codeine is not licensed for children under 12.

51
Q

How is morphine metabolised and excreted?

A

Morphine is metabolised to morphine-6-glucuronide, which is more potent than morphine and renally excreted.

52
Q

What happens to morphine in renal failure?

A

It accumulates, increasing the risk of respiratory depression.

53
Q

How should morphine dosing be adjusted for patients with <30% renal function?

A

Reduce the dose and increase the timing interval.

54
Q

What alternative to morphine is recommended in renal failure?

A

Use oxycodone instead, and consult guidelines if in doubt.

55
Q

What is tramadol, and when was it introduced?

A

Tramadol is a weak opioid agonist, slightly stronger than codeine, introduced in 1977.

56
Q

How does tramadol work as a prodrug?

A

Tramadol is metabolised by CYP2D6 to o-desmethyl tramadol, which is its active form. It is ineffective in about 10% of patients lacking CYP2D6 activity.

57
Q

What secondary effect does tramadol have?

A

Tramadol acts as a serotonin and norepinephrine reuptake inhibitor, contributing to its analgesic effect.

58
Q

What interactions should be considered when prescribing tramadol?

A

It interacts with SSRIs, tricyclic antidepressants, and MAOIs, potentially leading to fatal outcomes. Caution is needed when prescribing to patients on antidepressants.

59
Q

Why has tramadol become a controlled drug?

A

Due to a rise in deaths associated with its misuse, tramadol is now a controlled drug with stricter controls on long-term prescriptions.

pharmacology (7 decks)

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