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Opioid and benzodiazepine antagonists are an important component of an anesthesiologists’ armamentarium. Anesthesiologists rely on these agents for rapid reversal of adverse effects such as respiratory depression and loss of responsiveness. This may be especially important in the context of restoring ventilation in hypoxic patients either by antagonizing the ventilatory depressant effect of opioids or antagonizing the sedating properties of benzodiazepines so that patients can be prompted to breathe. Furthermore, select antagonists may also play an important role in other pathologic conditions, including tumor progression in selected types of cancer. This chapter will provide a brief overview of commonly used opioid and benzodiazepine antagonists. A summary of each reversal agent is presented in Table 7–1.
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First synthesized in 1961, naloxone is indicated for the complete or partial reversal of opioid sedation and respiratory depression. It is also indicated for suspected opioid intoxication and has been proposed as an adjunctive agent in the management of septic shock.1
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Naloxone is a pure opioid antagonist. Although its mechanism of action is not fully understood, in vitro studies suggest that it competes for the μ, k, and σ opiate receptor sites of the central nervous system (CNS). When administered in the absence of opioid activity, it has no effect.1
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The most rapid onset of action is achieved by intravenous (IV) injection. Intramuscular (IM) or subcutaneous (SQ) injections are also possible but may have unreliable absorption patterns. Endotracheal administration is also an option when intravascular access is unavailable. Because the duration of action for many opioids is longer than that of naloxone, patients should be closely monitored following administration.1
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For opioid overdose, an initial IV dose of 0.4 to 2 mg may be given. This may be repeated at 2- 3-minute intervals. In the case of postoperative respiratory depression, naloxone hydrochloride can be injected in 0.04- to 0.2-mg increments at 2-minute intervals until the desired reversal is achieved. Excessive or rapid reversal can induce nausea, vomiting, sweating, or circulatory arrest.1
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In suspected opioid overdose, an initial dose of 0.01 mg/kg is given. A subsequent dose of 0.1 mg/kg may be given if the initial dose does not result in adequate clinical improvement. In children with postoperative opioid respiratory depression, IV naloxone can be administered in 0.005- to 0.01-mg increments at 2- to 3-minute intervals until adequate reversal is achieved. Children should be monitored for at least 24 hours following administration.1
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Onset/Duration of Action
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Onset of action for IV administration is approximately 2 minutes, and its half-life is approximately 1 hour in adults2 and approximately 3 hours in neonates....