Question
An 85-year-old man with advanced-stage prostate cancer comes to the physician because of a 1-week history of worsening lower back and hip pain. The patient’s analgesic regimen includes oxycodone, ibuprofen, and alendronic acid. Physical examination shows localized tenderness over the lumbar spine and right hip. His current pain management requires opioid dose escalation. Which of the following opioid side effects is most likely to remain unaffected by the mechanism underlying this patient’s need for a higher drug dose?
| A. |
Constipation
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| B. |
Pruritus
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| C. |
Mydriasis
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| D. |
Nausea
|
Show Answer
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Correct Answer � A
Explanation
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Ans-A-Constipation
Constipation
Constipation is a side effect of chronic opioid use, mediated by both µ-opioid receptor and opioid receptor agonism. Opioids tend to slow gastrointestinal transit with a severity of constipation relative to opioid dose. Patients generally do not develop tolerance to constipation, so it does not improve with chronic opioid use.
Opioid tolerance develops when repeated agonism of the d-opioid receptor leads to its desensitization so that it can only be activated by greater doses of the agonist (i.e., the opioid).
Pruritus
Pruritus secondary to mast cell activation and histamine release is a common side effect of opioid use. However, as patients continue on a consistent and prolonged course of opioids, tolerance develops and the risk of pruritus decreases.
Nausea
Nausea is a common side effect of opioid use. However, the phenomenon of tolerance is such that nausea usually resolves with prolonged and consistent opioid dosing.
Mydriasis
Mydriasis is not a typical opioid side effect; however, opioids do usually cause miosis. Miosis is mediated by µ-opioid receptor agonism, a different mechanism than the development of tolerance. Miosis in chronic opioid use is resistant to tolerance.
