Morphine - IV

Question 1

What is the pharmacologic category/class of morphine?

Answer 1

• Opioid Analgesic — Naturally occuring

_{Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lesson 4. Classification, Relative Potency & Opioid Abuse}

Question 2

What is the mechanism of action of morphine?

Answer 2

Opioid rececptor agonism, especially mu and some delta

• Presynaptic: decreases cAMP-dependent influx of calcium ions → inhibition of neurotransmitter release
• Post synaptic: increased outward K⁺ conductance → hyperpolarization of nerve cell

resultant increase in pain threshold, altered pain perception, and **inhibition ascending pain pathways **

_{Anesthesia Guidebook - Episode 17: Anesthesia Top Drawer Run Down - Part 1
Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lesson 2. Opioid Receptors
Nagelhout (7th ed.), pp. 141 - Fig. 11.2, 142, 1295-1296
Stoelting’s Pharmacology (5th ed.), pp. 218-219}

Question 3

What is the typical dose range of morphine for analgesia in adults?

Emphasis because ranges may vary depending on patient/procedure

Answer 3

• 1-4 mg IV q1-2 hrs PRN

Ranges are as wide a 1-20 mg, but IV morphine is not very popular…

_{Anesthesia Guidebook - Episode 17: Anesthesia Top Drawer Run Down - Part 1
UpToDate - Morphine: Drug Information}

Question 4

What is the onset of action for morphine?

Answer 4

• Rapid/immediate with maximal effects in ~20 minutes

_{Nagelhout (7th ed.), p. 1298
Stoelting’s Pharmacology (5th ed.), p. 231
UpToDate - Morphine: Drug Information}

Question 5

What is the duration of action for morphine?

Answer 5

• 4-6 hrs

Duration related to hydrophilic properties, active metabolites

_{Anesthesia Guidebook - Episode 17: Anesthesia Top Drawer Run Down - Part 1
Nagelhout (7th ed.), p. 1298
UpToDate - Morphine: Drug Information}

Question 6

What organ(s) are responsible for morphine’s clearance (metabolism/elimination)?

Answer 6

• Metabolism: Liver
• Elimination: Kidneys

active metabolites - caution in renal failure

Half-life: ~2-4 hours

_{Anesthesia Guidebook - Episode 17: Anesthesia Top Drawer Run Down - Part 1
Stoelting’s Pharmacology (5th ed.), p. 228
UpToDate - Morphine: Drug Information}

Question 7

True or False:

Morphine-6-glucuronide, a metabolite of morphine, is more potent than the parent drug

Answer 7

• True — this is a major consideration for patients with renal failure

_{Anesthesia Guidebook - Episode 17: Anesthesia Top Drawer Run Down - Part 1
Nagelhout (7th ed.), p. 147}

Question 8

Cardiovascular effects of morphine include:

Answer 8

• Bradycardia
• Arterial/venous dilation → ↓ SVR/BP — likely minimal in healthy, supine, normovolemic patients
  _{attributed to release of histamine}

Note that these are similar to those of other opioids

Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lessons 2 & 3

Nagelhout (7th ed.), pp. 143, 147

Stoelting’s Pharmacology (5th ed.), p. 221

Question 9

What are the respiratory effects of morphine?

Answer 9

• Dose dependent depression of ventilation — RR affected before Vt
  _{(shifting of the CO2 response curve)}
• Inhibits hypoxic ventilatory drive
• Apnea at large doses

Note that these are similar to those of other opioids

Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lessons 2 & 3

Nagelhout (7th ed.), p. 142

Stoelting’s Pharmacology (5th ed.), p. 222

Question 10

What are the effects of morphine on the CNS?

Answer 10

• Sedation
• Miosis/pinpoint pupils
• Mild hypothermia
  _{resets hypothalamic temperature setpoint}
• N/V
  _{Partial dopamine agonists at CTZ}

Note that these are similar to those of other opioids

Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lessons 2 & 3

Nagelhout (7th ed.), p. 142

Stoelting’s Pharmacology (5th ed.), p. 222

Question 11

True or false:

Because of morphine’s pharmacokinetic profile, sedation serves as a reliable indicator of appropriate analgesia

Answer 11

• False

Sedation precedes analgesia following IV morphine administration

Nagelhout (7th ed.), p. 147

Question 12

What are the GI/GU effects of morphine?

Answer 12

• Delayed gastric emptying
• Slowed peristalsis → CONSTIPATION
• N/V
• Contraction of sphincter of Oddi → biliary colic
  _{evidence is kind meh on this}
• Urinary retention (IDGAF)
  _{detrusor relaxation, urinary sphincter constriction}

Note that these are similar to those of other opioids

Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lessons 2 & 3

Nagelhout (7th ed.), pp. 143-144

Stoelting’s Pharmacology (5th ed.), pp. 223-224

Question 13

BONUS

Which of these opioids is more hydrophilic?

• Morphine
• Fentanyl

Answer 13

• Morphine

Nagelhout (7th ed.), p. 147

Stoelting’s Pharmacology (5th ed.), p. 231

Question 14

The experience of pain can be divided into four steps: transduction, transmission, modulation, and perception. Which of these does morphine have an effect on?

Answer 14

Along with other opioids, fentanyl effects

• transduction
  _{peripheral nerves}
• modulation
  _{spinal cord}
• perception
  _{brain/brainstem}

Apex Unit 5: Pharmacology 2; Opioid & Non-Opioid Analgesics; Lessons 1 & 2