NARCOTIC ANALGESICS
Opioid analgesics are the narcotic analgesics obtained from the opium plant. More than 20 different alkaloids are obtained from the unripe seed of the opium poppy plant. The analgesic properties of opium have been known for hundreds of years. The narcotics obtained from raw opium (also called the opiates, opioids, or opiate narcotics) include morphine, codeine, hydrochlorides of opium alkaloids, and camphorated tincture of opium. Morphine, when extracted from raw opium and treated chemically, yields the semisynthetic narcotics hydromorphone, oxymorphone, oxycodone, and heroin.Heroin is an illegal narcotic in the United States and is not used in medicine. Synthetic narcotics are those man-made analgesics with properties and actions simi-lar to the natural opioids. Examples of synthetic narcotic analgesics are methadone, levorphanol, remifen-tanil, and meperidine. Additional narcotics are listed in the Summary Drug Table: Narcotic Analgesics.
ACTIONS
Narcotic analgesics are classified as agonists, partial agonists, and mixed agonists-antagonists. The agonist binds to a receptor and causes a response. A partial agonist binds to a receptor, but the response is limited (ie, is not as great as with the agonist). Antagonists bind to a recep-tor and cause no response. An antagonist can reverse the effects of the agonist. This reversal is possible because the antagonist competes with the agonist for a receptor site.
An agonist-antagonist has properties of both the agonist and antagonist. These drugs have some agonist activity at the receptor sites and some antagonist activity at the receptor sites.
Classification of the narcotic analgesics is based on their activity at the opioid receptor sites. Although five
categories of opioid receptors have been identified, only three of these receptors affect the action of the narcotic analgesics:
• mu
• kappa
• delta
The narcotic agonists have activity at the mu and kappa receptors (and possi-bly the delta sites). Remifentanil is a very short-acting agonist with potent analgesic activity. It is a mu opioid agonist with rapid onset, peak effect, and short duration of action. The mixed agonist-antagonist drugs act on the mu receptors by competing with other substances at the mu receptor (antagonist activity) and are agonists at other receptors. Partial agonists have limited agonist activity at the mu receptor. The actions of the narcotic analgesics on the various organs and structures of the body (also called secondary pharmacological effects) are
USES
The major use of the narcotic analgesic is to relieve or manage moderate to severe acute and chronic pain. The ability of a narcotic analgesic to relieve pain depends on several factors, such as the drug, the dose, the route of administration, the type of pain, the patient, and the length of time the drug has been administered. Morphine is the most widely used opioid and an effective drug for moderately severe to severe pain. Morphine is considered the prototype or “model” narcotic. Morphine’s actions, uses, and ability to relieve pain are the standards to which other narcotic analgesics are often compared.Other narcotics, such as meperidine and levorphanol, are effective for the treatment of moderate to severe pain. For mild to moderate pain, the primary health care provider may order a narcotic such as codeine or pentazocine.
In addition to the relief or management of moderate to severe acute and chronic pain, the narcotic analgesics may be used for the following reasons:
• To lessen anxiety and sedate the patient before surgery. Patients who are relaxed and sedated when
anesthesia is given are easier to anesthetize (requiring a smaller dose of an induction anesthetic), as
well as easier to maintain under anesthesia
• Support of anesthesia (ie, as an adjunct during
anesthesia)
• Obstetrical analgesia
• Relief of anxiety in patients with dyspnea associated
with pulmonary edema
• Intrathecally or epidurally for pain relief for
extended periods without apparent loss of motor,
sensory, or sympathetic function
• Relief of pain associated with a myocardial infarc-
tion (morphine)
• Management of opiate dependence (levomethadyl)
• Detoxification of and temporary maintenance of
narcotic addiction (methadone)
• To induce conscious sedation before a diagnostic
or therapeutic procedure in the hospital setting
• Treatment of severe diarrhea and intestinal
cramping (camphorated tincture of opium)
• Relief of severe, persistent cough (codeine, although
the drug’s use has declined)
Use in Management of Opioid Dependence
Two opioids are used in the treatment and management of opiate dependence: levomethadyl and methadone.Levomethadyl is given in an opiate dependency clinic to maintain control over the delivery of the drug. Because of its potential for serious and life-threatening proarrhythmic effects, levomethadyl is reserved for use in the treatment of addicted patients who have no response to other treatments. Levomethadyl is not taken daily; the drug is administered three times a week (Monday/Wednesday/Thursday or uesday/Thursday/
Saturday). Daily use of the usual dose will cause serious overdose.
Methadone, a synthetic narcotic, may be used for the relief of pain, but it also is used in the detoxifi-cation and maintenance treatment of those addicted to narcotics. Detoxification involves withdrawing the patient from the narcotic while preventing withdrawal symptoms.Maintenance therapy is designed to reduce the
patient’s desire to return to the drug that caused addic-tion, as well as to prevent withdrawal symptoms. The dosages used vary with the patient, the length of time the individual has been addicted, and the average amount of drug used each day. Patients enrolled in an outpatient methadone program for detoxification or
maintenance therapy on methadone must continue to receive methadone when hospitalized.
ADVERSE REACTIONS
The adverse reactions differ according to whether the narcotic analgesic acts as an agonist or as an agonistantagonist.
Agonists
One of the major hazards of narcotic administration is respiratory depression, with a decrease in the respira-
tory rate and depth. The most common adverse reactions include light-headedness, dizziness, sedation, constipation, anorexia, nausea, vomiting, and sweating.
When these effects occur, the primary health care provider may lower the dose in an effort to eliminate or
decrease the intensity of the adverse reaction. Other adverse reactions that may be seen with the administration of an agonist narcotic analgesic include:
• Central nervous system—euphoria, weakness,headache, pinpoint pupils, insomnia, agitation,tremor, and impairment of mental and physical tasks
• Gastrointestinal—dry mouth and biliary tractspasms
• Cardiovascular—flushing of the face, peripheral circulatory collapse, tachycardia, bradycardia, and palpitations
• Genitourinary—spasms of the ureters and bladder sphincter, urinary retention or hesitancy
• Allergic—pruritus, rash, and urticaria
• Other—physical dependence, pain at injection site, and local tissue irritation
Agonist-Antagonists
Administration of a narcotic agonist-antagonist may result in symptoms of narcotic withdrawal in those addicted to narcotics. Other adverse reactions associated with the administration of a narcotic agonist antagonist include sedation, nausea, vomiting, sweating, headache,vertigo, dry mouth, euphoria, and dizziness.
CONTRAINDICATIONS
All narcotic analgesics are contraindicated in patients with known hypersensitivity to the drugs. These drugs are contraindicated in patients with acute bronchial asthma, emphysema, or upper airway obstruction and
in patients with head injury or increased intracranial pressure. The drugs are also contraindicated in patients with convulsive disorders, severe renal or hepatic dysfunction, acute ulcerative colitis, and increased intracranial pressure. The narcotic anal-gesics are Pregnancy Category C drugs (oxycodone,Category B) and are not recommended for use during pregnancy or labor (may prolong labor or cause respi-ration depression of the neonate). The use of narcotic analgesics is recommended during pregnancy only if the benefit to the mother outweighs the potential harm to the fetus.
PRECAUTIONS
These drugs are used cautiously in the elderly and in patients with undiagnosed abdominal pain, liver dis-ease, history of addiction to the opioids, hypoxia,supraventricular tachycardia, prostatic hypertrophy, and renal or hepatic impairment. The obese must be monitored closely for respiratory depression while tak-ing the narcotic analgesics. The drug is used cautiously during lactation (wait at least 4 to 6 hours after taking the drug to breastfeed the infant). The narcotics are used cautiously in patients undergoing biliary surgery because the drug may cause spasm of the sphincter of Oddi.
INTERACTIONS
The narcotic analgesics potentiate the central nervous system (CNS) depressant properties of other CNS
depressants, such as alcohol, antihistamines, antide-pressants, sedatives, phenothiazines, and monoamine oxidase inhibitors. Use of the narcotic analgesics within 14 days of the MAO inhibitors may potentiate the effect of either drug. Patients taking the agonist-antagonist narcotic analgesics may experience withdrawal symptoms if the patient has been abusing or using narcotics. The agonist-antagonists drugs can cause opioid with drawal symptoms in those who are physically dependent on the opioids. There is an increased risk of respiratory depression, hypotension, and sedation when narcotic analgesics are administered too soon after barbiturate general anesthesia.
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