Opiods Flashcards by Sophie Wakeling

What is nociception?

Non-conscious neural traffic due to trauma or potential trauma to tissue

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What is pain?

Complex, unpleasant awareness of sensation modified by experience, expectation, immediate context and culture.

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How do you feel pain?

Nociceptors stimulated
Release of substance P and glutamate.
Afferent nerve stimulated
Fibres decussate
Action potential ascends
Synapses in thalamus
Project to post central gyrus

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How can we modulate pain?

Have modulators in peripheral system and in central system.

Peripherally: Substantia Gelatinosa

Centrally: Peri-aqueductal grey

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How can we modulate pain peripherally?

Tissue damage then through Ad and C fibres to the substantia gelatonosa then up spinothalamic tract to the thalamus.

Also, if we ‘rub it better’ it stimulates the Ab fibres which simulate the lamina and cause inhibition of Ad and C fibres.

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How do we modulate pain centrally?

Pain acting on thalamus and cortex stimulate the Periaqueductal grey matter.

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MOP

Supraspinal / GI tract

Decreased cAMP

Outward flux of potassium

Hyperpolarisation and decrease Substance P release

Enkephalins and B-endorphins

Analgesia, depression, euphoria, dependence, respiratory sedation

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DOP

Wide distribution

Decreased cAMP

Influx of Ca

Hyperpolarisation and decrease of substance P release

Enkephalins

Analgesia, inhibit dopamine, modulate u

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KOP

Spinal cord / Brain / Periphery

Decreased cAMP

Efflux of potassium, Influx of calcium.

Hyperpolarisation and decrease substance P release.

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Describe the WHO analgesic ladder

Simple analgesia e.g. paracetamol / NSAIDs

Weak opioid e.g Codeine

Strong opioid e.g. Morphine, fentanyl

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What do you take for arthritic pain?

NSAIDS

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What do you take for neuropathic pain?

Anticonvulsants
Tricyclics
SSRIs
SNARIs

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Describe the opiods as a class

Exploit natural opioid receptors either agonise or antagonise

Main therapeutic effects via u-receptors

Aim to modulate pain

Also indicate in cough, diarrhoea, palliation

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How can you give morphine?

PO, IV, IM, SC, PR

But, gut absorption can be erratic

Significant first pass effect - 40% oral bioavailability.

IV and SC tend to be better.

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Describe distribution, metabolism and elimination of morphine

Distribution: Rapidly enters all tissues including foetal
Struggle to cross blood-brain barrier.

Metabolism: Morphine + glucuronic acid - M6G + M3G

Eliminated renally.

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On what receptors does morphine mostly act?

U (MOP) receptors - complete activation of u.

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How does morphine work?

Analgesia

Euphoria

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What are the side effects of morphine?

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Respiratory Depression - medullary resp centre less responsive to CO2.

Emesis - stimulate CTZ

GI tract - decrease motility, increasing sphincter tone

Cardiovascular

Miosis

Histamine release - careful with asthmatics.

Describe the absorption, distribution, metabolism and elimination of Fentanyl

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Absorption: IV, epidural, Intrathecal, Nasal

Distribution: Highly lipophilic, highly protein bound, high level of CNS crossing

Metabolism: Hepatic via CYP3A4

Elimination: Half life 6 minutes, renally excreted

How is fentanl different to morphine?

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100% potency - MUCH more potent

Higher affinity fo u receptor.

Actions of fentanyl

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Analgesia

Anaesthetic

What are the side effects of fentanyl?

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Respiratory distress
Constipation
Vomitting

Describe the absorption, metabolism and elimination of codeine

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Absorption: PO, SC administration

Metabolism: Codeine to morphine via CYP2D6. This enzyme has extremely variable expression. CYP2D6 inhibited by fluoxetine.

Elimination: Glucoronidation of morphine and renal excretion

How potent is codeine compared to morphine?

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Approx 1/10th potency

Describe the actions of codeine

Mild to moderate analgesia | Cough depressant

What are the side effects of codeine?

Constipation | Respiratory depression - worse in children

Describe absorption, metabolism and elimination of Buprenorphine

Absorption: Transdermal, Buccal, Sublingual Distribution: Very lipophilicity Metabolism: Hepatic via CYP3A3 then glucoronidation before biliary excretion. Elimination: Biliary > Renal Safe in renal impairment Half life 37 hours.

How does buprenorphine compare to morphine?

``` Very high affinity for u receptor. Low Kd. Long duration of action Not easily displaced Lower Emax as partial agonist, lower efficacy Antagonist at k receptors. ```

What can you use buprenorphine for?

Moderate to severe pain | Opioid addiction treatment

What are the side effects of buprenorphine?

Respiratory depression Low Bp Nausea Dizziness

Describe the absorption, metabolism and elimination of Naloxone

Absorption: IV, IM, Intranasal, PO Very low oral bioavailability as extensive first pass effect Rapid onset of action Distribution: Rapid distribution as very lipophilic Metabolism: Hepatic - naloxone-3-glucuronide Renal excreted Elimination: Duration of action 30-60mins

How does naloxone compare to morphine?

Affinity u>d>k Greased affinity than morphine Affinity less than buprenorphine

What are the actions of naloxone?

Competitive antagonism of opioids.

What are the side effects of naloxone?

Short half life | Slow infusion

Describe how opioid tolerance occurs

Up-regulate by making more receptors so synthetic bind and endogenous no longer cause a response.

What do you use for opioid withdrawal?

Methadone - reduced E(max) and reduced side effects

Why is overdose a growing problem?

As abusing drugs prescribes and abusing drugs need as not got opioids anymore. Prescribe short courses a much as you can.

Describe an overdose of opioids

u receptor Variable effects of doses Respiratory depression most common cause of death Can decrease effects - d agonist, 5HT4 agonists Naloxone infusion as treatment.

What symptoms do you get in an overdose of opioids?

``` Dependace Vomiting Constipation Hypotension and bradycardia Decreased sex drive Histamine release Miosis Drowsiness Respiratory depression Apnoea ```

What groups of patients require special consideration?

``` Manual labourers / drivers Elderly Bedbound Asthmatics Biliary tract obstruction Respiratory disease Renal impairment Pregnancy ```

In who are opioids completely contraindicated?

``` Hepatic failure Acute respiratory distress Comatose Head injury - as already disrupt blood brain barrier Raised ICP ```

How do you prescribe opioids in palliative prescribing>

Difficult as Harold Shipman Tend to ignore special considerations Indications: Pain, Shortness of breath Manage side effects: Nausea, constipation

What do opioids prescriptions have to include?

Date and prescribers address and full name. Patient address and name Form of the drug - tablets, syrup, capsules, catches, ampoules ect. Units - mg, mls, ect. Total volume - words and figures Clearly defined doses.

Why are opioids controlled under the misuse of drugs legislations?

Aim to prevent: Misuse Illegal obtainment Harm being caused

Opiods Flashcards

(44 cards)