5 Questions
In which type of patients does morphine retain its normal analgesic efficacy?
Extensive metabolizers
Which of the following opioids is known to be less effective in poor metabolizers?
Codeine
What is the primary factor influencing the analgesic potency of opioids like morphine?
Opioid receptor binding affinity
Which of the following is NOT a factor affecting the pharmacokinetics of morphine?
Opioid receptor expression
What is the primary reason why codeine and morphine are effective in normal subjects?
Their efficient metabolism by CYP2D6
Study Notes
Opioid Metabolism and Efficacy
- Codeine is ineffective in patients who cannot convert it to morphine (poor metabolizers), as shown in a volunteer study (Fig. 17.15)
- Morphine retains its normal analgesic efficacy in poor metabolizers
- Codeine and morphine are effective in normal subjects (extensive metabolizers)
Dose-Effect Relationship
- Tolerance is characterized by a rightward shift in the dose-effect curve (Fig. 17.19)
- Hyperalgesia is characterized by a downward shift in the dose-effect curve (Fig. 17.19)
Opioid-Induced Hyperalgesia
- Opioid-induced hyperalgesia is distinct from tolerance
- Hyperalgesia is associated with a downward shift in the dose-effect curve (Fig. 17.19)
Meta-Analysis and Guidelines
- A recent meta-analysis confirmed the efficacy of opioids in pain management (108)
- Treatment guidelines regarding patient selection are still evolving (109)
This quiz covers the effects of fentanyl and codeine on pain relief in patients, including their pharmacokinetics and pharmacodynamics. It also discusses the differences between poor and extensive metabolizers.
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