Morphine

What is Morphine? ¹

• Naturally occurring opioid analgesic derived from the opium poppy.
• Used for the management of moderate to severe pain.

Mechanism of Action & Pharmacokinetics ¹²

• Primarily acts on mu-opioid receptors in the central nervous system (CNS) to produce analgesia.
• Onset in 30-60 minutes (PO) and 15 minutes (IV), with a half-life of 2-3 hours. ³
• Metabolized in the liver by glucuronidation, producing morphine-3-glucuronide (inactive) and morphine-6-glucuronide (active), the latter of which has potent analgesic effects.
  • Morphine-6-glucuronide can accumulate in renal failure, potentially causing prolonged sedation and respiratory depression. ¹
• Excreted primarily through the kidneys.

Pharmacodynamics ¹²

Cardiovascular

• May cause mild to moderate hypotension due to peripheral vasodilation (in part due to histamine release)
• Can also cause bradycardia due to its effects on the parasympathetic nervous system.

Respiratory

• Depresses respiratory centers in the brainstem, leading to decreased respiratory rate and minute ventilation. Often, compensatory increased tidal volume occurs. ¹
• Risk of respiratory depression increases with dose and concomitant use of other CNS depressants.

Indications ¹

• Pain ManagementPain Management
  Introduction
  Pain management can be a complex topic in anesthesia. Patient factors, like age, comorbidities, and pre-existing chronic pain can help guide analgesia during the operative period. Surg...: Management of moderate to severe pain where the use of an opioid analgesic is appropriate.
• Also used for relief of dyspnea in palliative care and management of myocardial infarction-related pain.

Dosage ²

• Oral:
  • 10 to 30 mg every 4 hours as needed for pain.
• Intravenous (IV):
  • 2.5 to 10 mg every 2 to 4 hours as needed for pain.
  • 0.05 to 0.1 mg/kg in pediatrics (IV). ⁴
• Patient-Controlled Analgesia (PCA):
  • Initial demand dose: 1 mg IV; lockout interval typically 6 to 10 minutes.
• Dosage should be adjusted based on the patient's response, tolerance, and severity of pain.

Contraindications ¹²

• Hypersensitivity to morphine or any of its components.
• Severe respiratory depression without resuscitative equipment or monitoring.

Complications ¹²⁵

• Respiratory depression
• Common opioid-related side effects include nausea, vomiting, constipation, pruritus, and sedation.
• Risk of hypotension, especially in patients with compromised blood pressure or on concomitant medications that lower blood pressure.
• Risk of prolonged sedation in patients with renal impairment due to accumulation of morphine-6-glucuronide.

References