Opioid Agonists-Antagonists

Opioid agonist-antagonists help relieve moderate to severe pain, and act as an adjunct to anesthesia.

Prototype and Other Medications

​​​​​​​​​​​​​​Butorphanol and pentazocine — Medication Classification: Opioid Agonists-Antagonists

The prototype medications for opioid agonist-antagonists are butorphanol and pentazocine. Butorphanol is only available as an injectable or nasal spray, whereas pentazocine, in combination with naloxone, is available in an oral form. Another medication in this category is buprenorphine.

Expected Pharmacologic Action

Opioid agonist-antagonists have mixed actions; they are mu receptor antagonists and kappa receptor agonists. These medications result in fewer mu-related adverse drug reactions, such as respiratory depression, euphoria, and dependence, but also produce milder analgesic effects. Opioid agonist-antagonists can precipitate withdrawal in clients addicted to opioids, so clients taking an opioid agonist-antagonist need to reveal their opioid use before administration.

Adverse Drug Reactions

The adverse drug reactions of opioid agonist-antagonists include limited respiratory depression, sedation, dizziness and lightheadedness, drowsiness, headache, and nausea. Both butorphanol and pentazocine increase cardiac workload, so avoid using in clients who have a disorder that affects cardiac output. Abstinence syndrome may occur in clients who become dependent on one of these medications, but the withdrawal manifestations are much less severe than those you might see with opioid-dependent clients. Abstinence syndrome, also called withdrawal syndrome, is a set of physical and psychological manifestations that occur when a client stops or decreases how much medication is consumed. Opioid withdrawal manifestations include abdominal cramps, diarrhea, agitation, anxiety, hypertension, tachycardia, tremors, muscle pain, pupil dilation, runny nose, and insomnia. 

Interventions

When caring for a client on an opioid agonist-antagonist, ask them about their opioid use before administering this medication. Measure clients’ baseline vital signs and closely monitor respirations. If a client’s respiratory rate falls below 12/min, withhold the medication and stimulate breathing. Monitor clients when ambulating if they experience dizziness or lightheadedness and consider recommending an alternative medication if nausea does not resolve. Make sure that you don’t administer opioid agonist-antagonists to clients with myocardial infarction or cardiac insufficiency.

Safety Alert

It is your responsibility to ensure that clients do not receive medications that can cause adverse drug reactions related to other prescribed medications or a client’s other medical disorder. Be sure you understand not only your client’s current diagnosis but other medical disorders in the medical history. Prior to administration, check the medical record of all your clients medications in case there are medication interactions or medical conditions that contradict the use of a prescribed medication. If you are concerned that there might be a contraindication to the use of a medication, clarify the prescription with the provider before administering the medication. If you do not and proceed with administering the medication, you may be liable for the consequences if the client has an adverse reaction.

Administration

You can administer opioid agonist-antagonists intramuscularly, intravenously, or intranasally. You give pentazocine orally, and often use it when an invasive route is not warranted, or clients self-administer the medication as part of pain management regimen. Measure clients’ baseline vital signs prior to administration and monitor throughout therapy. Do not give either medication if the respiratory rate is less than 12/min. For intranasal administration of butorphanol, give one spray into one nostril and repeat every 60 to 90 minutes as needed. For preoperative IM administration, give it 60 to 90 min as prescribed before surgery. Monitor both medications’ therapeutic effects to make sure they provide effective pain relief. Remember to avoid discontinuing either medication abruptly if a client is on it for an extended period of time.

Client Instructions

When instructing clients on their use of an opioid agonist-antagonist, make sure they know to take this medication only when needed and on a short-term basis. Tell them not to take the medication prior to driving or activities that require mental alertness. If they experience dizziness or get lightheaded, remind clients to sit or lie down to prevent falls. Changing positions gradually may also minimize these effects. Instruct clients not to use these types of medications for anginal pain due to their effect on cardiac output. Also, clearly emphasize that they should not take opioids while taking an opioid agonist-antagonist.

Contraindications and Precautions

Clients who have acute myocardial infarction or are dependent on opioids should not take butorphanol or pentazocine. Both medications are schedule IV controlled substances, so use them with caution for clients who have a history of substance use disorder. Also, take caution in clients who have a head injury or increased intracranial pressure, reduced respiratory reserve, hepatic or renal disease, or cardiac insufficiency, as well as clients who have hypertension.

Interactions

Don’t give opioid agonist-antagonists with other CNS depressants, such as barbiturates, phenobarbital, benzodiazepines, and alcohol, because they will increase CNS depression and the risk of respiratory depression. Administration of an opioid agonist-antagonist with an opioid, however, will actually decrease the effects of the opioid.