DRUG CLASSES
Opioid antagonist
An antagonist is a substance that counteracts the action of something else. A drug that is an opioid antagonist has a greater affinity for a cell receptor than an opioid drug (agonist), and by binding to the cell it prevents a response to the opioid. Thus, an opioid antagonist reverses the actions of an opioid. One of the most severe adverse reactions to opioid treatment is respiratory depression. Specific antagonists have been developed to reverse the respiratory depression associated with the opioids. Naloxone is capable of restoring respiratory function within 1 to 2 minutes after administration. Naltrexone (another antagonist) is used primarily to treat alcohol dependence and to block the effects of suspected opioids if they are being used by a person undergoing treatment for alcohol dependence.
OPIOID ANTAGONISTS
Actions
Administration of an antagonist prevents or reverses the effects of opioid drugs. The antagonist reverses the opioid effects by competing for the opiate receptor sites and displacing the opioid drug (see Chapter 15). If the individual has taken or received an opioid, the effects of the opioid are reversed. An antagonist drug is not selective for specific adverse reactions. When an antagonist is given to reverse a specific adverse reaction, such as respiratory depression, it is important to remember the antagonist reverses all effects. Therefore, a patient who receives an antagonist to reverse respiratory effects will also experience a reversal of pain relief; that is, the pain will return. If the individual has not taken or received an opioid, an antagonist has no drug effect.
PHARMACOLOGY IN PRACTICE
When Mr. Park came to the preoperative unit, he complained that the pain on his back (where the shingles rash was erupting) was greater than the pain in his broken hip and leg. On rounds before the surgical procedure to repair his femur, the primary health care provider assured him that the acyclovir would begin to alleviate some of the pain from the rash. Following the surgical procedure, the surgeon ordered meperidine (Demerol) for postoperative pain management. In assessing Mr. Park, he reported his pain is “8 out of 10” on a 0 to 10 pain scale. The nurse promptly gives the drug, and approximately 20 minutes after receiving an injection of meperidine, the nurse discovers Mr. Park’s vital signs are as follows: blood pressure 80/50 mm Hg, pulse rate 130 bpm, and respiratory rate 8 breaths/minute.
Now that you have read almost all the chapters in this unit, determine whether you could anticipate Mr. Park’s risks for opioid toxicity and discuss what actions should be taken for a proper pain assessment and medication administration.
Uses
Opioid antagonists are used for the treatment of the following:
- Postoperative acute respiratory depression
- Opioid adverse effects (reversal)
- Suspected acute opioid overdosage
Adverse Reactions
Generalized reactions include:
- Nausea and vomiting
- Sweating
- Tachycardia
- Increased blood pressure
- Tremors
See the Summary Drug Table: Opioid Antagonists for more information.
Contraindications, Precautions, and Interactions
Antagonists are contraindicated in those with a hypersensitivity to the opioid antagonists. Antagonists are used cautiously in those who are pregnant (pregnancy category B), in infants of opioid-dependent mothers, and in patients with an opioid dependency or cardiovascular disease. These drugs also are used cautiously during lactation.
These drugs may produce withdrawal symptoms in individuals who are physically dependent on the opioid. Antagonists may prevent the action or intended use of opioid antidiarrheals, antitussives, and analgesics.
NURSING PROCESS
PATIENT RECEIVING AN OPIOID ANTAGONIST FOR RESPIRATORY DEPRESSION
ASSESSMENT
Preadministration Assessment
Patients involved in long-term opioid therapy for pain relief build tolerance to the physical adverse effects of the drugs. It is the patient who does not use opioids routinely and who is being given an opioid drug for acute pain relief or a surgical procedure who is at most risk for respiratory depression after opioid administration (Fig. 16.1). These patients are described as opioid naive.
Sometimes the somnolence and pain relief produced by the opioid drug will slow the patient’s breathing pattern. This can be alarming if the respiratory rate you have been monitoring has been rapid because of anxiety and pain. The first step is to make efforts to arouse the patient and coach his or her breathing pattern if possible. Before administration of the antagonist, take the blood pressure, pulse, and respiratory rate, and review the record for the drug suspected of causing the symptoms of respiratory depression. If there is sufficient time, review the initial health history, allergy history, and current treatment modalities.
Ongoing Assessment
As part of the ongoing assessment during the administration of the antagonist, continue to monitor the blood pressure, pulse, and respiratory rate at frequent intervals, usually every 5 minutes, until the patient responds. This monitoring should be more frequent if respiratory depression occurs in the immediate postoperative setting. After the patient has shown a response to the drug, monitor vital signs every 5 to 15 minutes. Notify the anesthesiologist or primary health care provider if any adverse drug reactions occur because additional medical treatment may be needed. Continue to monitor the respiratory rate, rhythm, and depth; pulse; blood pressure; and level of consciousness until the effects of the opioid wear off.
NURSING ALERT
The effects of some opioids may last longer than the effects of naloxone (Narcan). A repeat dose of naloxone may be ordered if results obtained from the initial dose are unsatisfactory. The duration of close patient observation depends on the patient’s response to the administration of the opioid antagonist.
Figure 16.1 Patients who are in acute pain following a surgical procedure and do not use opioids routinely are more at risk for respiratory depression. (Photo by B. Proud.)
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