Opioids Flashcards
Through what method of relieving pain do opioids work?
Modulate central pain awareness
What is the source of opioid analgesics?
Seed pods of the opium poppy
What are 2 principal alkaloids of opioid analgesics?
- Morphine
2. Codeine
What are the 2 classifications of opioids?
- Full agonists (strong)
2. Partial agonists (weak)
Name 2 places where natural opioids occur
- Juice of the opium poppy
2. Endogenous endorphins
What 2 ways can opioids be prepared if they are not natural?
- Prepared from morphine to form semisynthetic opioids e.g. heroin
- Synthesized from precursor compounds to form synthetic opioids e.g. fentanyl
Name 8 primary pharmacological effects of opioids
- Sedation / Anxiolytic
- Depression of respiration
- Cough suppression
- Pupillary constriction
- Nausea and vomiting
- GIT symptoms
- Release histamines causing allergic reaction
- Affect white blood cell and immune function
What 4 ways is the sedation effect of opioids seen?
- Drowsiness
- Apathy
- Cognitive impairment
- Sense of tranquillity
What is the main life threatening pharmacological effect of opioids?
Depression of the respiratory system, especially if opioids taken with alcohol
How do opioids affect the GIT?
Cause constipation
Give an overview of an opioid’s mechanism of action
Act presynaptically to inhibit substance P release, which is caused by activation of peripheral nociceptive fibres and other pain-signalling neurotransmitters from nerve terminals in the dorsal horn of the spinal cord
What is the target of opioids?
G-protein coupled opioid mu receptors in the CNS and PNS
What is the cellular effect of opioids agonising G-protein coupled opioid mu receptors?
- Closure of calcium channels on the presynaptic membrane
- Opening of potassium channel on postsynaptic membrane
Name 3 opioid pain receptors
- Mu
- Kappa
- Delta
What are 2 types of mu receptors?
- Mu-1
2. Mu-2
What is the location and function of Mu-1 receptors?
Located outside spinal cord and responsible for central interpretation of pain
What is the location of Mu-2 receptors?
Located throughout CNS
Name 4 functions of Mu-2 receptors
- Respiratory depression
- Spinal analgesia
- Physical dependence
- Euphoria
Name 4 characteristics of kappa receptors
- Modest analgesia
- Little to no respiratory depression
- Little to no dependence
- Dysphoric effects
What is thought to be the main function of delta receptors?
Regulate Mu receptor activity and act as an overflow system
What is a pure agonist?
Affinity for binding plus efficacy
What is a pure antagonist?
Affinity for binding but no efficacy
What is a mixed agonist-antagonist?
Produces an agonist effect at one receptor and an antagonist effect at another
What is a partial agonist?
Affinity for binding but low efficacy
Why will 2 different opioids reduce pain relief?
Tend to antagonise each other as they compete for receptors
Name 2 weak opioids
- Codeine
2. Tramadol
Name 7 strong opioids
- Morphine
- Diamorphine
- Oxycodone
- Fentanyl
- Hydromorphone
- Methadone
- Buprenorphine
What is the approximate bioavailability of opioids?
50%
Describe 4 routes of administration of opioids and the latency to onset of each method
- Oral (15-30 mins)
- Intranasal (2-3 mins)
- Intravenous (15-30 secs)
- Pulmonary-inhalation (6-12 secs)
What is the duration of action of opioids?
4-72 hours depending on the substance in question
How are opioids metabolised?
Hepatic metabolism via phase 1 and phase 2 biotransformations to form a diverse array of metabolites e.g. morphine-6 glucuronide
What are 4 contraindications of prescribing opioids?
- Patients with impaired pulmonary function
- Patients with impaired hepatic or renal function
- Patients with hypothyroidism
- Patients with recent head injury
What is an alternative opioid to prescribe if the patient suffers from kidney impairment?
Oxycodone or fentanyl
Name 3 direct physiological adverse effects of opioid consumption
- Nausea and vomiting
- Constipation
- Confusion
How can constipation be relived if a patient is taking opioids?
A simulative laxative e.g. senna
What is tolerance?
A diminished responsiveness of the drug’s action represented by an increase in the minimum drug dose required to produce a given level of effect
Give 2 reasons why tolerance can occur in opioids
- Changes in binding of a drug to receptors
2. Changes in receptor transductional processes related to the drug of action
What is dependence?
Occurs when a drug is necessary for normal physiological functioning which is demonstrated by withdrawal reactions
How are withdrawal reactions usually characterised?
Usually opposite effect of the drug e.g. opioids cause goose-bumps, bowels switch-on and large pupils
Name 2 opioid antagonists
- Naloxone
2. Naltrexone
How do opioid antagonists act?
Competitive inhibition site blocking against agonist as they have a strong affinity for the Mu receptor
Why is it significant that naloxone has a shorter half life than opioids?
If a patient collapses of overdose a second dose of naloxone is needed after 30 minutes to ensure opioid is still antagonised
