opioid pharmacology Flashcards

1
Q

define oral bioavailability

A

the fraction of an oral administered drug that reaches systemic circulation

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2
Q

what is an opioid

A

powerful painkillers that are a class of drug related to heroin that interact with opioid receptors on nerve cells

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3
Q

what are the 5 kinds of opioids?

A
  1. naturally occurring opioids - from the opium poppy
  2. simple chemical modifications
  3. synthetic opioids
  4. synthetic partial agonists
  5. antagonists
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4
Q

when are opoids useful

A

for acute short term pain

cant help chronic pain

dangerously addictive

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5
Q

what are the routes of administration for opioids

A
  • Pharmacokinetics
  • Oral
  • Bioavailability
  • First pass metabolism by the liver – 50% of oral morphine is metabolized by the first pass metabolism. Halve the dose if given IM/ IV etc.
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6
Q

how long does a single dose of morphine last for

A

about 3-4 hours

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7
Q

what is the name of the legislation for controlled drug use?

A

Misuse of Drugs Act 1971

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8
Q

what class of drugs are opioids

A

class A

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9
Q

practical issues with opioids

A
  • Secure storage
  • CD books – two signatures needed
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10
Q

define pharmacodynamics

A

the study of the biochemical, physiologic, and molecular effects of drugs on the body and involves receptor binding (including receptor sensitivity), postreceptor effects, and chemical interactions.

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11
Q

what system do opioid drugs use

A

they simply use the existing pain modulation system

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12
Q

what are endogenous opioids

A

enkephalins and endorphins

primarily produced in the brain and have multiple actions throughout the body.

act at opioid receptors and their activity can be blocked by opioid antagonists.

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13
Q

what do G protein couples receptors do

A

act via second messengers

Inhibit the release of pain transmitters at spinal cord and midbrain – and modulate pain perception in higher centers – euphoria – changes the emotional perception of pain

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14
Q

how do opioids work?

A
  1. Descending inhibition of pain
  2. Part of the fight or flight response
  3. Never designed for sustained activation
  4. Sustained activation leads to tolerance and addiction
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15
Q

define potency

A

whether a drug is ‘strong’ or ‘weak’ relates to how well the drug binds to the receptor, the binding affinity.

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16
Q

define effiacy

A

the concept of full or partial agonists

is it possible to get a maximal response with the drug or not?

17
Q

define tolerance

A

down regulation of the receptors with prolonged use.
Need higher doses to achieve the same effect

18
Q

describe dependance

A

psychological – craving, euphoria

19
Q

describe opioid withdrawal

A

starts within 24 hours, lasts about 72 hours

20
Q

where do opioid receptors exist

A

outside the pain system e.g. digestive tract, respiratory control centre

21
Q

how are opioids given

A

sometimes epidurally

mostly systemically

22
Q

7 side effects of opioids

A
  • Respiratory depression
  • Sedation
  • Nausea and vomiting
  • Constipation
  • Itching
  • Immune suppression
  • Endocrine effects
23
Q

how to give dosage of opioids

A

start with a small dose and titrate up as necessary as different patients have quite a range of sensitivity to opioids

24
Q

describe metabolism of morphine

A

Morphine is metabolized to morphine 6 glucuronide which is more potent than morphine and is renally excreted.

With normal renal function this is cleared quickly

In renal failure it will build up and may cause respiratory depression

Be careful in patients with <30% renal function (creatinine clearance <30). Reduce dose and timing interval.

25
Q

give 5 common opoids

A
  • hydrocodone (Vicodin®) oxycodone (OxyContin®, Percocet®)
  • oxymorphone (Opana®)
  • morphine (Kadian®, Avinza®)
  • codeine.
  • fentanyl.
26
Q
A