6. Analgesia - Codeine Flashcards
When and where were opiates first isolated from?
1803 from the white poppy (papaver somniferum)
What is considered the most potent opiate?
morphine
What are opiates referred to as acting on?
central acting analgesia
What do opiates act on?
µ, δ and κ opioid receptors
What kind of metabolism do opiates undergo?
1st pass metabolism, conjugated in the liver
What is the approx. half life of opiates?
3 hours
What kind of pain is morphine used for?
acute severe pain - continuous dull (rather than sharp intermittent)
What CNS effects does morphine have?
drowsiness, sedation and euphoria
(does not effect touch, pressure, vision, hearing)
What are some of the unwanted effects of morphine?
- nausea and vomiting (intitial)
- urticaria/pruritis
- respiratory depression
- constipation (GI motility)
- eye signs (mitosis - pinpoint pupils)
- confusion in the elderly
Why does morphine commonly cause nausea and vomiting?
due to direct stimulation of the chemoreceptors in the medulla and as such often need an antiemetic
What is the oral dosage for morphine?
10-30mg every 4 hours as required
What is the IV dosage for morphine?
2.5-15mg/70kg / 4 hours
What is the IM dosage of morphine?
10mg, works in 30 mins and lasts for 4-5 hours
What is the SC dosage of morphine?
5-20mg/70kg every 4 hours
What tends to be the max dose of morphine given per 24 hours?
100mg in 24 hours
What are the contraindications and special considerations for morphine?
- dependence
- ulcerative colitis + AAC
- suspected head injury
- acute alcoholism
- reduced respiratory reserve
- upper airway obstruction
- acute asthma
- poisoning or toxins (constipation will stop clearing of this)
- hepatic and renal insufficiency
- hypersensitivity to opiates
What are the signs of an opioid overdose?
- asleep and difficult to wake
- low resp. rate
- low BP
- pupil constriction which tends not to respond to light
- cold and clammy skin
- flaccid skeletal muscle including tongue with resultant airway compromise
How would you treat an opioid overdose?
establish airway and administer naloxone 04mg IV ever 2-3mins
What are codeine/dihydrocodeine?
naturally occurring opioids
How are codeine and dihydrocodeine taken?
oral opioid
What are codeine and dihydrocodeine antagonists at?
µ opioid receptors
What kind of pain are codeine and dihydrocodeine used for?
mild to moderate acute and chronic pain
What is codeine/dihydrocodeine often used in combination with?
paracetamol - cocodamol/cohydramol
What causes codeine to be analgesic?
codeine alone doesn’t have much analgesic effect, but it is metabolised in the liver to give about norcodeine and 10% morphine which is primarily responsible for the analgesic activity
Dose to dose, what is the potency of codeine compared to morphine?
8-10% the potency of morphine
Where is codeine metabolised?
the liver
What is the half life of codeine?
3 hours
How long does the analgesic effect of codeine lasts?
2-4 hours
Why do some patients get little analgesic efficacy from codeine?
about 7% of the population lack the CYP450 2D6 receptors responsible for the drug biotransformation in the liver
What are ‘ultrametabolisers’ of codeine?
group of people with high efficiency of turning codeine into morphine and some of these patients start to feel very unwell with nausea and vomiting due to higher levels of morphine
What are the contraindications and side effects of codeine?
mimic those of morphine but at a lower level:
- nausea
- hypotension
- urticaria/pruritis
- respiratory (low chance)
- constipation (when used longer term)
- dependence/tolerance (not a high chance)
What is the standard adult dose of codeine?
30-60mg 4-6 hourly
(maximum 240mg in 24 hours)
What are the indications and uses of codeine?
- mild-moderate pain
- postoperative pain
- step 2 on WHO ladder as an opiate adjunct
- NSAIDs contraindicated
- antitussive
- antidiarrhoeal
Is codeine useful for dental pain?
not so much on its own but yes in combination with paracetamol (cocodamol)
What are the principle interactions of codeine?
- alcohol
- antihistamines
- anxiolytics and hypnotics
- antipsychotics
What can the interaction of codeine with alcohol cause?
enhanced hypotension
What can the interaction of codeine with antihistamines cause?
increased sedative effect
What can the interaction of codeine with anxiolytics and hypnotics?
enhanced sedative effect
What can the interaction of codeine with antipsychotics cause?
increased sedative effect and enhanced hypotension
Why must you beware of giving codeine to a patient with diarrhoea of an unknown origin?
patient may have ingested a toxin etc or have the likes of a c diff infection that they’re body is trying to clear, and the antidiarrhoeal effects of codeine would be undesirable
What special considerations should be made when giving codeine to certain patients?
- Beware in Diarrhoea
- Constipation (GI issues)
- 7% Caucasian Population uneffective
- ‘ultrametabolisers’
- Dependency (long term use)
What are some of the combined preparations of codeine available?
- Cocodamol=paracetamol/codeine (most common)
- Codyramol=paracetamol/dihyrocodeine
- Co-proxamol=paracetamol/ dextropropoxyphene
- Cocodaprin=aspirin/codeine
- Solpadeine, solpadol, paracodol, tylex (on public sale)
What drugs may need to be taken alongside opioids?
anti-emetics and laxatives
What is ‘NNT’?
the number of patient who need to receive the active drug for one to achieve at least 50% relief o pain compared with placebo over a 4-6 hour treatment period
What do more effect drugs have an NNT of, and what does this mean?
- more effect drugs have a lower NNT - of just over 2
- in essence this means that for ever two patient who receive the drug one patient will get at least 50% relief because of the treatment
