Other than asking the patient if a particular agent has worked or not worked in the past, it is not possible to determine which opioid may work best for a given patient. There are, however, some agents which should not be used, at least first line, in the postoperative setting. Codeine is not a good first choice due to the fact that possibly around 10-15% of the population does not have an active form of the enzyme (i.e., cytochrome P450 2D6) necessary to convert codeine into the active drug, morphine. Morphine is relatively contraindicated in patients with severe renal insufficiency due to the accumulation of the metabolite, morphine-6-glucuronide, which can lead to sedation and respiratory depression. Meperidine is not recommended as its active metabolite, normeperidine, can accumulate in a day or two to levels that cause nervous system excitation (tremors, muscle twitching, convulsions). In addition it causes a strong euphoric feeling especially when given intravenous (IV) push and it usually causes more nausea than other agents. Propoxyphene is not recommended because its active metabolite, norpropoxyphene, can accumulate when high doses are used, if renal or hepatic insufficiency exists or in the elderly, leading to nervous system toxicity. Hydrocodone use needs to be monitored closely because of the acetaminophen component in the available preparations which can lead to acetaminophen toxicity. Also, the most frequent non-medical use of a pharmaceutical agent leading to emergency department visits is hydrocodone combination preparations (Weinger 2007).
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