Opioids Flashcards
What is the main problem with opioids ?
Highly addictive, subject to misuse and abuse
Define opium, opioid, and opiate.
Opium: Natural extract of the poppy Papaver somniferum. It contains morphine and other related compounds (e.g. codeine).
Opioid: any substance (natural or synthetic) that produces morphine like effects which are blocked by a morphine antagonist
Opiate: any naturally occurring opioid
What is the main action of opioids they are used for ?
Their analgesic action
Differentiate between strong and weak opioids (what distinguishes them?)
Weak opioids have a “ceiling effect” where escalation of the dose typically causes SE without improving analgesia
Strong opioids do NOT (higher dose = higher effect + higher SEs), and are pure mu agonists
What is the main difference between different opioids, other than wether they are weak or strong. G
Vary mainly by:
- Duration of action
- Potency
Identify an example of long lasting, and short lasting opioid.
SHORT-ACTING:
Remifentanyl (infusion, lasts for seconds to minutes, metabolised by plasma esterases)
Fentanyl
LONG-ACTING
Methadone (lasts about 24 hrs)
What is the standard starting dose for morphine ? for fentanyl ? Why such a difference ?
PARENTERAL
Morphine: 10 mg (0.1 mg/kg)
Fentanyl: 100 micograms (1- 2micrograms /kg)
ORAL
Morphine: 30mg (0.3mg/kg)
Fentanyl: N/A
Difference because fentanyl much more potent
What is one reason a patient may have to switch opioid ? How may we determine how much of the next opioid we need to give ?
If ORAL opioid, and need more, or can physically not take it, may have to switch.
There are equivalencies between different opioids (refer to slide 7).
If change from oral to IV opioid, need to reduce dose.
Identify the main strong, and weak opioids.
STRONG • Morphine • Oxycodone • Diamorphine • Fentanyl • Pethidine • Remifentanil • Methadone
WEAK
Codeine
Dihydrocodeine
Tramadal
RELATED AGENTS
Loperamide
ANTAGONISTS
Naloxone
Naltrexone
What is the effect of most drugs in overdose on the pupils ? of opioids ?
In overdose, most drugs will give you dilated pupils
Opioids will give you pinpoint pupil
What is the class of drug of diamorphine ? What are its main indications ? Why isn’t it used more ?
Sem-synthetic opioid, more water soluble
Palliative care patients who requires large doses of opioids (can give this in a smaller V of fluid)
SE: More buzz (liable to misuse and abuse)
Identify a route of administration for fentanyl.
Transdermal patch
Identify side effects of Pethidine.
Anti-cholinergic side effects
What are the main indications for Naloxone and naltrexone ? State the route of administration of each.
Naloxone: acute opioid toxicity (injection)
Naltrexone: given to people who are drug free after addiction problem, to stay off drug (by mouth)
Describe the main indications of Loperamide amongst opioids, and its mechanism of action.
No analgesic effect
Action on myenteric plexus of gut, helpful in cases of diarrhea (will constipate you)
Identify a side effect of Tramadol.
Serotoninergic effects means can feel down if cease treatment.
Identify the main administration routes for opioids, stating an example of indication where each may be appropriate).
IV
ORAL- (ideal for patients under treatment for cancer/ongoing care)
TRANSDERMAL PATCH- Fentanyl (absorbed through skin, may be used if patient is drowsy, or for patients with stable managed pain since absorption may vary) (can also be absorbed in oral mucosa)
CENTRALLY- In epidural or spinal anaesthetia, can put opioid with local anesthetic (at VERY low dose of opioid)
IM Injections
Describe the process of absorption of oral opioids.
Most opioids are weak bases. In the stomach, they remain in ionised form, and are therefore poorly absorbed. They tend to be absorbed into the bloodstream in the intestine (pH allows them to be unionised), and subsequently head to liver where undergo first pass metabolism (into active compounds e.g. codeine or into active metabolites) by CYP450. They then enter systemic circulation.
Many opioids have active metabolites, which are excreted by kidneys (problematic if renal failure)
What is the main problem associated with transdermal patches (e.g. for Fentanyl).
Absorption will cary depending on dilation of blood vessels to the skin. E.G. if fever, or hot water bottle over area then increased absorption, and if patient cold or skin perfusion impaired then decreased absorption and patient may become sore.
Define patient controlled analgesia.
Patient is in control of amount of drug they use. Safety feature present so if patient too drowsy to press button, cannot give themselves another drug of dose.
Identify an opioid which is actually a prodrug. How does it produce its effects ?
Codeine is a prodrug, and has no effects. It has to be metabolised into a morphine by the liver before it actually has effects.
Different groups metabolite it in different ways:
- 10% of Caucasians are slow metabolisers
- 30% Africans are ultrafast metabolisers
i.e. for given dose, Africans get much larger dose on average
State the bioavailability of the following:
- Morphine
- Oxycodone
- Fentanyl
- Codeine
- Tramadol
- Morphine: 30%
- Oxycodone: 70%
- Fentanyl: 50% (lozenge)
- Codeine: 60%
- Tramadol: 70%
Identify the main opioid receptors.
- mu opioid peptide receptor (MOP)
- Kappa (KOP)
- Delta (DOP)
- Nociception (NOP)
Identify the main sites in the body where opioid act.
Opioid receptors are widespread but more densely found where there is nervous tissue involved in pain transmission.
Opioid receptors are found in:
- PAG
- Peripheral tissues
- Peripheral afferent nerve terminals
- Nociceptors in peripheral tissues
- Cortex
- Thalamus
- Myenteric plexus
