opioid pharmacology Flashcards
define oral bioavailability
the fraction of an oral administered drug that reaches systemic circulation
what is an opioid
powerful painkillers that are a class of drug related to heroin that interact with opioid receptors on nerve cells
what are the 5 kinds of opioids?
- naturally occurring opioids - from the opium poppy
- simple chemical modifications
- synthetic opioids
- synthetic partial agonists
- antagonists
when are opoids useful
for acute short term pain
cant help chronic pain
dangerously addictive
what are the routes of administration for opioids
- 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.
how long does a single dose of morphine last for
about 3-4 hours
what is the name of the legislation for controlled drug use?
Misuse of Drugs Act 1971
what class of drugs are opioids
class A
practical issues with opioids
- Secure storage
- CD books – two signatures needed
define pharmacodynamics
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.
what system do opioid drugs use
they simply use the existing pain modulation system
what are endogenous opioids
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.
what do G protein couples receptors do
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
how do opioids work?
- Descending inhibition of pain
- Part of the fight or flight response
- Never designed for sustained activation
- Sustained activation leads to tolerance and addiction
define potency
whether a drug is ‘strong’ or ‘weak’ relates to how well the drug binds to the receptor, the binding affinity.
define effiacy
the concept of full or partial agonists
is it possible to get a maximal response with the drug or not?
define tolerance
down regulation of the receptors with prolonged use.
Need higher doses to achieve the same effect
describe dependance
psychological – craving, euphoria
describe opioid withdrawal
starts within 24 hours, lasts about 72 hours
where do opioid receptors exist
outside the pain system e.g. digestive tract, respiratory control centre
how are opioids given
sometimes epidurally
mostly systemically
7 side effects of opioids
- Respiratory depression
- Sedation
- Nausea and vomiting
- Constipation
- Itching
- Immune suppression
- Endocrine effects
how to give dosage of opioids
start with a small dose and titrate up as necessary as different patients have quite a range of sensitivity to opioids
describe metabolism of morphine
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.
give 5 common opoids
- hydrocodone (Vicodin®) oxycodone (OxyContin®, Percocet®)
- oxymorphone (Opana®)
- morphine (Kadian®, Avinza®)
- codeine.
- fentanyl.
