McKenna's Pharmacology for Nursing, 2e

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P A R T 4  Drugs acting on the central and peripheral nervous systems

Contraindications and cautions Opioid antagonists are contraindicated in the presence of any known allergy to any opioid antagonist to avoid hypersensitivity reactions . Caution should be used in the following circumstances: during pregnancy and breastfeeding because of potential adverse effects on the fetus and neonate ; with opioid addiction because of the precipitation of a withdrawal syndrome ; and with cardiovascular (CV) disease, which could be exacerbated by the reversal of the depressive effects of opioids. Adverse effects The most frequently seen adverse effects associated with these drugs relate to the blocking effects of the opioid receptors. The most common effect is an acute opioid abstinence syndrome that is characterised by nausea, vomiting, sweating, tachycardia, hypertension, tremu- lousness and feelings of anxiety. A naloxone challenge should be administered before giving naltrexone to help to avoid acute reactions. CNS excitement and reversal of analgesia are espe- cially common after surgery. Cardiovascular (CV) effects related to the reversal of the opioid depression can include tachycardia, blood pressure changes, dys- rhythmias and pulmonary oedema. Drug–drug interactions To reverse the effects of buprenorphine or dextropro- poxyphene, larger doses of opioid antagonists may be needed. Prototype summary: Naloxone Indications: Complete or partial reversal of opioid depression; diagnosis of suspected opioid overdose. Actions: Pure opioid antagonist; reverses the effects of the opioids, including respiratory depression, sedation and hypotension. Pharmacokinetics: Route Peak Onset Duration IV Unknown 2 mins 4–6 hours IM, SC Unknown 3–5 mins 4–6 hours T 1/2 : 30 to 81 minutes; metabolised in the liver, excreted in the urine. Adverse effects: Acute opioid abstinence syndrome (nausea, vomiting, sweating, tachycardia, fall in blood pressure), hypotension, hypertension, pulmonary oedema.

O pioid antagonists The opioid antagonists (Table 26.1) are drugs that bind strongly to opioid receptors but do not activate them. They block the effects of the opioid receptors and are often used to block the effects of too many opioids in the system. The opioid antagonists in use include naloxone ( Narcan ) and naltrexone ( Naltraccord , ReVia ). Therapeutic actions and indications The opioid antagonists block opioid receptors and reverse the effects of opioids, including respiratory depression, sedation, psychomimetic effects and hypotension. These agents are indicated for reversal of the adverse effects of opioid use, including respiratory depression and sedation, and for treatment of opioid overdose. (See Table 26.1 for usual indications for each opioid antag- onist agent.) The opioid antagonists do not have an appreciable effect in most people, but individuals who are addicted to opioids experience the signs and symptoms of withdrawal when receiving these drugs rapidly. Pharmacokinetics Opioid antagonists may be administered parenterally (SC, IM or IV) or orally. These drugs are well absorbed after injection and are widely distributed in the body. They undergo hepatic metabolism and are excreted pri- marily in the urine. ■ ■ Provide thorough teaching, including drug name, prescribed dose and schedule of administration; measures for avoidance of adverse effects; warning signs that may indicate possible problems; safety measures such as avoiding driving, getting assistance with ambulation, avoiding making important decisions or signing important papers; and the need for monitoring and evaluation to enhance the person’s knowledge about drug therapy and to promote compliance. Evaluation ■ ■ Monitor the person’s response to the drug (relief of pain, sedation). ■ ■ Monitor for adverse effects (CNS changes, GI depression, respiratory depression, arrhythmias, hypertension). ■ ■ Evaluate the effectiveness of the teaching plan (person can give the drug name and dosage and describe possible adverse effects to watch for, specific measures to prevent them and warning signs to report). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen.