Fentanyl Pharmacological Properties
Fentanyl is approximately 80-100 times more potent than morphine, making option B the correct answer. 1
Analysis of Each Option
A. It is normally found in the body
This is incorrect. Fentanyl is a synthetic opioid that was structurally designed by Paul Janssen in the early 1960s 2. It is not an endogenous compound naturally produced in the human body.
B. 100 times more potent than morphine
This is correct. According to multiple guidelines, fentanyl is approximately 80-100 times more potent than morphine:
- The EAPC guidelines state that fentanyl is "about 80 times as potent as parenteral morphine" 1
- The Critical Care guidelines indicate that "fentanyl is more lipid soluble and thus has higher bioavailability" and is "100 times more potent than morphine" 1
- Pharmacokinetic research confirms that fentanyl is "100-fold more potent than morphine" 2
C. It has twice as long as duration of action as morphine
This is incorrect. Fentanyl actually has a shorter duration of action compared to morphine when administered intravenously. Fentanyl's high lipophilicity allows it to cross quickly between plasma and central nervous target sites with a transfer half-life of 4.7-6.6 minutes 2. While transdermal fentanyl provides extended release over 72 hours, this is due to the delivery system rather than the intrinsic properties of the drug itself 1, 3.
D. It results in hypotension because of histamine release
This is incorrect. Unlike morphine, fentanyl does not cause significant histamine release. The FDA drug label specifically states: "Histamine assays and skin wheal testing in clinical studies indicate that clinically significant histamine release rarely occurs with fentanyl administration. Clinical assays show no clinically significant histamine release in dosages up to 50 mcg/kg." 3 Additionally, "at therapeutic dosages, fentanyl usually does not exert major effects on the cardiovascular system" 3.
Key Pharmacological Properties of Fentanyl
- Potency: 80-100 times more potent than morphine 1, 2
- Lipophilicity: Highly lipophilic (octanol:water partition coefficient >700) 2
- Metabolism: Undergoes first-pass metabolism via cytochrome P450 3A 2
- Bioavailability: ~30% after oral administration, 50-90% for transmucosal or intranasal formulations 2
- Histamine release: Minimal to none, unlike morphine 3
- Cardiovascular effects: Minimal at therapeutic doses 3
Fentanyl's high potency and lipophilicity make it particularly useful for transdermal administration, where it can be delivered at a constant rate over 72 hours, making it suitable for chronic pain management 1, 3, 4.