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Opiates are a group of naturally occurring compounds derived from the juice of the poppy Papaver somniferum. Morphine is the classic opiate derivative used widely in medicine; heroin (diacetylmorphine) is a well-known, highly addictive street narcotic. The term opioids refers to these and other derivatives of naturally occurring opium (eg, morphine, heroin, codeine, and hydrocodone) as well as new, totally synthetic opiate analogs (eg, fentanyl, butorphanol, meperidine, and methadone [Table II–43]). A wide variety of prescription medications contain opioids, often in combination with aspirin or acetaminophen. Dextromethorphan (See Dextromethorphan) is an opioid derivative with potent antitussive but no analgesic or addictive properties. Tramadol (Ultram) is an analgesic that is unrelated chemically to the opiates but acts on mu-opioid receptors and blocks serotonin reuptake. Butorphanol is available as a nasal spray with rapid absorption. Buprenorphine is a partial opioid agonist that is approved for treatment of opioid addiction. Suboxone is a sublingual tablet containing buprenorphine plus naloxone to reduce intravenous abuse. Tapentadol (Nucynta) is a new mu-opioid agonist that also inhibits the reuptake of norepinephrine.

Table II-43 Opiates and Opioidsa

  1. Mechanism of toxicity

    1. In general, opioids share the ability to stimulate a number of specific opiate receptors in the CNS, causing sedation and respiratory depression. Death results from respiratory failure, usually as a result of apnea or pulmonary aspiration of gastric contents. In addition, acute noncardiogenic pulmonary edema may occur by unknown mechanisms.

    2. Pharmacokinetics. Usually, peak effects occur within 2–3 hours, but absorption may be slowed by the pharmacologic effects of opioids on GI motility. Slow-release preparations of morphine (eg, MS-Contin) or oxycodone (eg, OxyContin) may have a delayed onset of action and prolonged effects. With fentanyl patches, dermal absorption can continue even after removal. Smoking or ingesting fentanyl patches can result in rapid and high levels. Most of these drugs have large volumes of distribution (3–5 L/kg). The rate of elimination is highly variable, from 1–2 hours for fentanyl derivatives to 15–30 hours ...

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