Opioid Misuse Flashcards
What are opioids?
Substances which bind to opioid receptors
Includes both naturally occurring opiates (eg. morphine) and synthetic opioids (eg. buprenorphine and methadone)
Type of analgesic
What is the MOA of opioids?
- Exert their effects primarily through agonist activity at opioid receptors, which are widely distributed throughout CNS and PNS
- Three major classes of opioid receptors: mu (µ), delta (δ), and kappa (κ).
- Opioids predominantly act on mu receptors, mediating their analgesic, euphoric, and respiratory depressive effects.
Endogenous opioids (eg. endorphins, enkephalins, and dynorphins) modulate pain perception and other physiological processes.
Exogenous opioids can be classified into natural (e.g., morphine, codeine), semi-synthetic (e.g., oxycodone, hydrocodone), and synthetic (e.g., fentanyl, methadone) compounds.
What are indications for opioid use?
Pain:
- incl chronic and non-cancer pain
Anaesthesia:
- Commonly used as adjuncts during GA for analgesia, sedation, and hemodynamic stability
Opioid dependence treatment:
- Methadone and buprenorphine used in maintenance therapy and detoxification programs for opioid-dependent patients.
Antitussive and antidiarrheal effects:
- Codeine and loperamide have been utilized for their antitussive and antidiarrheal properties, respectively.
What are adverse effects of opioids?
Respiratory depression:
- By suppressing the brainstem respiratory centres.
Sedation:
- Induce sedation by inhibiting release of neurotransmitters and dampening neuronal activity.
Constipation:
- Reduce GI motility, leading to constipation and other GI sx.
N + V:
- Stimulate chemoreceptor trigger zone, causing N + V
Pruritus:
- May induce histamine release –> pruritus and other allergic-type reactions.
Tolerance and dependence:
- Prolonged opioid use can –> tolerance, requiring higher doses to achieve the desired effect, and physical dependence, necessitating continued use to avoid withdrawal symptoms.
What are features of opioid misuse?
rhinorrhoea
needle track marks
pinpoint pupils
drowsiness
watering eyes
yawning
What are complications of opioid misuse?
Viral infection secondary to sharing needles: HIV, hepatitis B & C
Bacterial infection secondary to injection: infective endocarditis, septic arthritis, septicaemia, necrotising fasciitis
VTE
Overdose may –> respiratory depression and death
Psychological problems: craving
Social problems: crime, prostitution, homelessness
What is the emergency management of opioid overdose?
IV or IM naloxone: has a rapid onset and relatively short duration of action
What are harm reduction interventions in opioid misuse?
needle exchange
offering testing for HIV, hepatitis B & C
How is opioid dependence usually managed?
- Managed by specialist drug dependence clinics although some GPs with a specialist interest offer similar services
- Pts may be offered maintenance therapy or detoxification
1st line in opioid detoxification: methadone or buprenorphine
- Compliance monitored using urinalysis
- Detoxification should last up to 4 weeks in an inpatient/residential setting and up to 12 weeks in the community
How does methadone work?
- A full agonist of the mu-opioid receptor - binds to these receptors in the brain and fully activates them.
- This action can relieve withdrawal symptoms and cravings.
- Has a long half-life
How does buprenorphine work?
- A partial agonist of the mu-opioid receptor and an antagonist of the kappa-opioid.
- Binds to mu-opioid receptors in the brain but only partially activates them.
- This partial activation is enough to alleviate cravings and withdrawal symptoms in individuals with opioid dependence.
- Furthermore, the binding of buprenorphine to the mu-opioid receptor is very strong, or ‘high affinity,’ meaning it can displace other opioids from these receptors and prevent them from exerting their effects.
- As a kappa-opioid receptor antagonist, buprenorphine may contribute to its ability to reduce symptoms of opioid withdrawal and potentially reduce depressive and dysphoric states.
