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Chapter 10: Opioid Pharmacology

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A 55-year-old woman is having a colonoscopy. Aside from other medications for sedation, it is likely she will receive which of the following analgesics?

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a. Methadone

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b. Meperidine

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c. Buprenorphine

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d. Fentanyl

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e. Pentazocine

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Answer is d. Fentanyl citrate and sufentanil citrate have widespread popularity as anesthetic adjuvants (see Chapter 11). They are used commonly either intravenously, epidurally, or intrathecally. The analgesic effects of fentanyl and sufentanil are similar to those of morphine and other opioids. Fentanyl is ~100 times more potent than morphine, and sufentanil is ~1000 times more potent than morphine. The time to peak analgesic effect after intravenous administration of fentanyl and sufentanil (~5 minutes) is notably less than that for morphine and meperidine (~15 minutes). Recovery from analgesic effects also occurs more quickly.

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A 42-year-old man with chronic pain is brought to the emergency room because of over-sedation and respiratory depression while using fentanyl patches. He is given intravenous naloxone. He is not given oral naloxone because naloxone

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a. is not absorbed from the GI tract.

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b. undergoes first-pass metabolism in the liver.

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c. is metabolized to an inactive metabolite in the GI lining.

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d. is excreted unchanged in the urine.

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e. is destroyed by stomach acid.

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Answer is b. Although absorbed readily from the GI tract, naloxone is almost completely metabolized by the liver before reaching the systemic circulation and thus must be administered parenterally. The drug is absorbed rapidly from parenteral sites of injection and is metabolized in the liver primarily by conjugation with glucuronic acid; other metabolites are produced in small amounts. The t1/2 of naloxone is ~1 hour, but its clinically effective duration of action can be even less.

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A 48-year-old man is being treated with a long-acting opiate for pain associated with terminal cancer. He is also prescribed a transmucosal fentanyl formulation (lollipop) for “breakthrough” pain. The transmucosal formulation is an effective analgesic because it

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a. avoids first pass metabolism of fentanyl.

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b. avoids nausea and vomiting that is associated with the systemic use of fentanyl.

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c. delivers fentanyl directly to opiate receptors in the mouth.

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d. avoids constipation.

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e. avoids respiratory depression.

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