Morphine when used for cancer palliative therapy least likely to cause:
**Core Concept**
Morphine, a potent opioid analgesic, is commonly used in cancer palliative therapy to manage severe pain. However, its use is associated with several side effects and risks, particularly in the context of palliative care. Understanding the pharmacological properties of morphine is crucial in predicting its effects and potential complications.
**Why the Correct Answer is Right**
Morphine is a prodrug that undergoes extensive first-pass metabolism in the liver, primarily by the enzyme CYP2D6, to form its active metabolite morphine-6-glucuronide (M6G). M6G is responsible for the analgesic effects of morphine. In cancer palliative therapy, morphine is often used for its analgesic properties, but its use can lead to several side effects, including respiratory depression, constipation, and cognitive impairment. However, one of the least likely side effects of morphine in this context is **myocardial infarction**.
**Why Each Wrong Option is Incorrect**
* **Option A:** Respiratory depression is a well-known side effect of morphine, particularly at higher doses. Morphine can cause respiratory depression by acting on the central nervous system, specifically the brainstem, where it binds to opioid receptors, leading to a decrease in respiratory rate and depth.
* **Option B:** Constipation is a common side effect of morphine, particularly in the context of long-term use. Morphine can decrease gastrointestinal motility, leading to constipation, by acting on the enteric nervous system and reducing the release of acetylcholine.
* **Option C:** Cognitive impairment is a potential side effect of morphine, particularly in elderly patients or those with pre-existing cognitive dysfunction. Morphine can cause cognitive impairment by affecting the central nervous system, specifically the hippocampus and other areas involved in memory and learning.
**Clinical Pearl / High-Yield Fact**
Morphine can be safely used in patients with renal impairment, as its active metabolite, M6G, is primarily excreted by the kidneys, but its effects are not significantly affected by renal function.
**Correct Answer:** D. Myocardial infarction