Opioid analgesics 4

Question 1

oral bioavailabilty and half-life of morphine

Answer 1

oral bioavailability 12-36%
Half-life 2-3 hours

Question 2

Explain the contraindications of morphine

Answer 2

Contraindications:
* Spontaneously breathing patients with raised intracranial pressure, head injury or other intracranial lesions
* Diarrhoea caused by poisons or antibiotic associated
pseudomembranous colitis

Question 3

List the drug interactions for morphine

Answer 3

Drug interactions:
* CNS depressants: alcohol, anaesthetic agents, sedatives, antipsychotics, antidepressants, antihistamines
* Antidiarrhoeals
* Anticholinergics
* Cimetidine
* Metoclopramide
* Monoamine oxidase inhibitors (for most opioids)

Question 4

explain the prescibers point of morphine

Answer 4

Prescriber’s points:
* When administering IV or IM to high-risk patients (obstructive sleepapnoea), equipment and expertise to ventilate and administer oxygen, andnaloxone should be available.
* Doses should be titrated and individualised
* Dependence liability in patient with a history of drug abuse, or whenadministered for prolonged periods
* Respiratory depression may aggravate elevation of ICP through CO2 retention and intracranial vasodilation, and miosis may mask pupil dilation
* Caution with patient with renal failure as active metabolite is excretedrenally
* Delayed respiratory depression may occur after intrathecal or epidural administration – monitor in high care environment for 24 hours
* Intrathecal and epidural preparation should be free from preservatives

Question 5

A transdermal analgesia

Answer 5

Fentanyl

Question 6

explain the use of fentanyl. explain which group of patient you use fentanyl with caution. when should it be prescribed

Answer 6

• Management of cancer pain
• Use with caution in chronic non-cancer patients
• Should only be prescribed by practitioners knowledgeable in in continuous administration of potent opioids
• Transdermal patch changed every 72 hours and applied in a different site
• Durogesic®

Question 7

Analgesia in severe pain, including post-operative and obstetric analgesia

Answer 7

Pethidine

Question 8

explain the pharmacokinectics of pethidine
Half-life:
Onset of analgesia
Duration of analgesia

Answer 8

Pharmacokinetics:
* Half-life: 2.5-4 hours; norpethidine (active metabolite, potentially neurotoxic) 8-21 hours
* Onset of analgesia:
* IV = 1 minute
* IM / SC 10-15 minutes
* Duration of analgesia: 2-4 hours

Question 9

explain the contraindication of pethidine

Answer 9

Contraindications:
* Spontaneously breathing patients with raised intracranial pressure, head injury or other intracranial lesions
* Diarrhoea caused by poisons or antibiotic associated
pseudomembranous colitis
* Renal failure or severe hepatic disease

Question 10

explain the use of pethidine in pregnancy

Answer 10

Pregnancy:
Widely used before and during labour (if neonatal respiratory depression, administer naloxone) Maternal dependence may lead to withdrawal symptoms in the neonate. Cut off time: if birth is expected within 3 -4 hours

Question 11

List the drug interaction of pethidine

Answer 11

Drug interactions:
* As for morphine
* Monoamine oxidase inhibitors
* Cimetidine
* Serotonergic agents (antidepressants) increase risk of serotonin syndrome

Question 12

Atypical opioid, with morphine receptor agonist action.

Answer 12

Tramadol

Question 13

explain the action of tramadol

Answer 13

Inhibits neuronal reuptake of serotonin and noradrenaline.
Use for moderate to moderate severe pain

Question 14

Pharmacokinectics for tramadol

Answer 14

Pharmacokinetics:
* Oral bioavailability 75%
* Onset of analgesic effects after 1 hour
* Primarily renal excretion about 30% unchanged drug

Question 15

Explain the contraindication of tramadol

Answer 15

Contraindications: raised ICP, head injury, respiratory depression Safety not established in pregnancy

Question 16

drug interaction of tramadol

Answer 16

Drug interactions:
* Carbamazepine
* CYP3A4 inhibitors
* CNS depressants, anaesthetics, alcohol
* Monoamine oxidase inhibitors
* Serotonergic agents: lead to serotonin syndrome

Question 17

preparations for tramadol

Answer 17

1. capsule/tablets: tramal, tramahexal, tramgesic
2. Combination with paracetamol: Tramacet

Question 18

explain the tolerance of opioids

Answer 18

• Tolerance: decrease in initial pharmacologic effect observed after chronic or long-term administration (for both the administered opioid and other opioid analgesics)
• Results from down-regulation of opioid receptors
• Tolerance develops to most of the effects of opioids but not to miosis and constipation.
• Although considerable tolerance to respiratory depression occurs, a sufficiently high dose of an opioid can still be fatal to highly opioidtolerant individuals.
• Tolerance is usually accompanied by a similar degree of physical dependence.