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Drugs > Opioids > Flashcards

Opioids Flashcards

1
Q

Name 7 effects of opioids?

A

sedation
analgesia
antitussiv
muscle relaxation
control of compulsive behaviour
support or right sided heart function
overresponsiveness to noises or sensory stimuli

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2
Q

Name 2 groups of opioids and their chemical structure?

A
  1. Phenanthrenes: morphine
    - three-ring nucleus
  2. Benzylisoquinoline derivatives: papaverine
    - ring structure with a tertiary amine nitrogen

Levorotatory are much more active agonists than dextrorotary

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2
Q

What is the mechanism of action of opioids?

A
  • bind to stereospecific opioid receptors in CNS + other sites
  • Receptor binding activates G proteins as second messengers –> modulates adenylate cyclase activity–> alters transmembrane transport of effectors
  • also interfere presynaptically with neurotransmitter release
  • receptor affinity correlates well with analgesic potency of pure agonists

These changes result in interruption of the pain message to the brain and a decreased sensation of pain within the brain.

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3
Q

Name 4 opioid receptors in CNS + gut?

A
  • μ-receptor (MOP)
  • k-receptor (KOP)
  • d-receptor (DOP)
  • opiate-like receptor 1 (OLR-1, nociceptin receptor, NOP)
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4
Q

Why can opioids lead to excitatory behaviour?

A
  • results from the effects of the drug on the hypothalamus
  • indirect activation of dopaminergic receptors (benzodiazepines and phenothiazines, can block this activation)
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5
Q

How do opioids cause CNS depression?

A

cerebral cortex

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6
Q

What side effect can arise if opioids are combined with tricyclic antidepressants?

A
  • hypotension.
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7
Q

What side effects can be noted when opioids are combined with monoamine oxidase inhibitors?

A
  • rare but severe and immediate reactions: excitation, rigidity, hypertension, severe respiratory depression
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8
Q

What effects do opioids have on the respiratory system and how are these effects mediated? What patients are of increased risk?

A
  • tachypnea (oxymorphone, hydromorphone)
  • respiratory depressants: reduce RR and tidal volume
    –> depress pontine and medullary respiratory centers
    –> produce a delayed response (altered threshold) and decreased response (altered sensitivity) to arterial CO2 –> retention of CO2
  • Bronchoconstriction
  • wooden chest

Increased risk:
- critically ill patients
- underlying airway obstruction (e.g., brachycephalic animals) - pulmonary disease

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9
Q

Why can opioid administration cause tachypnea?

A
  • excitation and/or alteration of the thermoregulation center
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10
Q

What cardiovascular effects do opioids cause?

A
  • minimal effects
  • vagally mediated bradycardia (responsive to anticholinergics)
  • affect ability of vascular system to compensate for positional and blood volume changes
  • some (methadone, morphine, meperidine) cause histamine release –> hypotension
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10
Q

How can morphine induced histamine release be minimised?

A

dilution with saline + given slowly over 10-20 min

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11
Q

Name 2 contraindications for morphine, methadone and meperidine usage and explain why?

A
  • mast cell tumors
  • histamine-based diseases

cause histamine release –> hypotension

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12
Q

What effects do opioids have on the GI tract?

A

initial stimulation (vomiting, defecation) followed by decrease in motility

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13
Q

What effects do opioids have on ADH?

A

Release of ADH

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14
Q

What effects do opioids have on the urinary tract?

A

urine retention due to bladder atony

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15
Q

What effects to opioids have on the body temperature and why?

A

hypothermia + hyperthermia (cats, drug + dosage dependant - buprenorphine did not result in hyperthermia)

thermoregulatory center in the hypothalamus is reset to a lower setting

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16
Q

How are opioids metabolised and excreted?

A

Matbolisation: hepatic conjugation
Excretion: renal in the urine

Exception: remifentanil - metabolisation through nonspecific plasma esterases

In general: Principal metabolites can be highly active (e.g. morphine)

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17
Q

Why can meperidine cause seizures?

A
  • meperidine’s metabolite normeperidine is a convulsant –> causes neurotoxicity and seizures
18
Q

What is the pharmacokinetic profile of opioids and how can this change in drug overdose?

A
  • elimination of first order
  • Opioid overdoses change kinetics of elimination from first order to zero order by saturating the processes responsible for elimination and thereby greatly prolonging the duration of action
19
Q

How are potency of opioids measured? What are the potencies of methadone, fentanyl, remifentanyl, buprenorphine, butorphanol, codein, hydromorphone, oxymorphone and meperidine?

A
  • relative potencies of opioids are compared with the potency of morphine on an “equal-analgesic” basis
  • pure-agonist opioids: maximum biologic effect (e.g., analgesia or respiratory depression) is relatively dosage-dependent.

methadone: 1
fentanyl: 100-150
remifentanyl: 200-300
buprenorphine: 50-100
butorphanol: 3-5
codeine: 1/10
hydromorphone: 10
oxymorphone: 10
meperidine: 1/5

20
Q

You choose morphine for an epidural analgesia. What dose would you use and what are your expected pharmacokinetics?

A
  • morphine (0.1 mg/kg)
  • onset of action: 30 minutes
  • lasting effect: 12 to 24 hours
21
Q

You want to add a local anaesthetic to your epidural analgesia? What would you choose, what dose would you use and what would be your reasoning behind thi?

A
  • bupivacain: 0.5 mg/kg
  • blunting of deleterious postoperative or injury-associated increases in stress hormone levels and the metabolic response to surgery
22
Q

Name 5 contraindication to epidural injection or catheter placement?

A
  • local infection
  • coagulopathy
  • neurologic dysfunction
  • marked obesity (which increases difficulty)
  • hypovolemia with hypotension (avoided unless IVF corrects hypotension)
23
Q

What are common side effects of morphine?

A

vomiting, diarrhoea, bradycardia
hypotension + bronchoconstriction (histamine release)
(less common if actually painful)

24
Q

What is the bioavailability of oral morphine?

A
  • may be effective in some dogs but individual variability in bioavailability
  • poorly and erratically absorbed from the GI tract
  • –> oral route is not to be recommended
25
Q

On what receptors does methadone work?

A
  • μ-receptor agonist
  • noncompetitive inhibitor of NMDA receptors
26
Q

What happens if a heat source is applied over a fentanyl patch?

A
  • can greatly increase uptake of the drug (cave: overdose)
26
Q

What is the onset of analgesia for a fentanyl patch and how long does it last?

A
  • does not occur until 12 to 24 hours after application
  • lasts 4 days
27
Q

What is the difference of long-term fentanyl and remifentanyl infusion and what is the reason for this?

A
  • recovery from fentanyl after long-term CRI is more prolonged than in remifentanil because remifentanil is eliminated by plasma esterases and does not rely on hepatic metabolisation
28
Q

What is the ceiling effect of butorphanol?

A

drug reaches a maximum effect and increasing the drug dosage does not increase its effectiveness

29
Q

Why may butorphanol be of benefit in patients with intracranial hypertension or increased ocular pressure?

A
  • less potential than agonist opioids to cause reflexive increases in intracranial pressure (ICP)
  • antitussive effect + less vomiting lead to less increase in ICP
  • antiemetic effect
30
Q

What class of opioids does buprenorphine beolong to?

A

partial-agonist opioid, with limited agonist activity at μ-receptors

31
Q

What is the ceiling effect of buprenorphine?

A

ceiling effect on respiratory depression, but not analgesia, as the dose is increased

32
Q

Why may buprenorphine be of benefit in patients with intracranial hypertension or increased ocular pressure?

A

does not stimulate vomiting

33
Q

Why is analgesic efficacy greater for IV/IM than SC administration of buprenorphine?

A

slow uptake and resultant low plasma concentration gradient following SC

34
Q

What is the bioavailability of oral transmucosal buprenorphine in cats and dogs?

A

50%

35
Q

What is Simbadol 1.8mg/ml?

A
  • higher concentration buprenorphine injectable
  • extended duration (24 hr, repeatable up to 3 days) at doses approximately 10-fold higher than standard doses
36
Q

What class of opioids does codein belong to?

A

pure μ-agonist

37
Q

What is the bioavailability of oral codein in dogs?

A
  • 4% –> very poor bioavailability
38
Q

Name 3 opioid antagonists and their duration of action?
Name 2 agents useful for partial reversal of pure-agonist opioids? What opioid can be difficult to reverse?

A

Antagonists:
1. naloxone (very short acting)
2. nalmefene (long-acting)
3. naltrexone (long-acting)

Partial antagonists:
1. butorphano
2. nalbuphine

buprenorphine can be difficult to reverse due to its great receptor affinity

39
Q

What is the mechanism of action of opioid antagonists?

A

bind with great affinity to the μ, k, and d opioid receptors, competitively displacing agonists with lesser affinity

40
Q

What analgesic effects do opioid antagonists have?

A
  • no analgesic activity
  • ultra-low doses of naloxone and naltrexone potentiate the antinociception of opioid agonists
41
Q

In what setting has naloxone been used in research apart from it’s effect as an opioids antagonist?

A
  • treatment of hypovolemic shock in dogs.
  • infusion of high doses of naloxone lead to reduction in splanchnic capacitance leading to an improvement in VR, MAP and CO
42
Q

What effects are reversed by opioid antagonists?

A
  • Sedation
  • respiratory depression
  • analgesia

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