Central Nervous System Depressants and Muscle Relaxants



Central Nervous System Depressants and Muscle Relaxants


Objectives


When you reach the end of this chapter, you will be able to do the following:



1 Briefly describe the functions of the central nervous system.


2 Contrast the effects of central nervous system depressant drugs and central nervous system stimulant drugs (see Chapter 13) as relates to their basic actions.


3 Define the terms hypnotic, rapid eye movement, rapid eye movement sleep interference, rapid eye movement rebound, sedative, sedative-hypnotic, sleep, and therapeutic index.


4 Briefly discuss the problem of sleep disorders.


5 Identify the specific drugs within each of the following categories of central nervous system depressant drugs: benzodiazepines, nonbenzodiazepines, muscle relaxants, and miscellaneous drugs.


6 Contrast the mechanism of action, indications, adverse effects, toxic effects, cautions, contraindications, dosage forms, routes of administration, and drug interactions of the following medications: benzodiazepines, nonbenzodiazepines, muscle relaxants, and miscellaneous drugs.


7 Discuss the nursing process as it relates to the nursing care of a patient receiving any central nervous system depressants and/or muscle relaxant.


8 Develop a thorough nursing care plan related to the use of pharmacologic and nonpharmacologic approaches to the treatment of sleep disorders.


Drug Profiles



Key Terms


Barbiturates A class of drugs that are chemical derivatives of barbituric acid. They are used to induce sedation. (p. 193)


Benzodiazepines A chemical category of drugs most frequently prescribed as anxiolytic drugs and less frequently as sedative-hypnotic agents. (p. 190)


Gamma-aminobutyric acid (GABA) The primary inhibitory neurotransmitter found in the brain. A key compound affected by sedative, anxiolytic, psychotropic, and muscle-relaxing medications. (p. 190)


Hypnotics Drugs that, when given at low to moderate dosages, calm or soothe the central nervous system (CNS) without inducing sleep but when given at high dosages cause sleep. (p. 189)


Non–rapid eye movement (non-REM) sleep The largest portion of the sleep cycle. It has four stages and precedes REM sleep. Most of a normal sleep cycle consists of non-REM sleep. (p. 189)


Rapid eye movement (REM) sleep One of the stages of the sleep cycle. Some of the characteristics of REM sleep are rapid movement of the eyes, vivid dreams, and irregular breathing. (p. 189)


REM interference A drug-induced reduction of REM sleep time. (p. 189)


REM rebound Excessive REM sleep following discontinuation of a sleep-altering drug. (p. 189)


Sedatives Drugs that have an inhibitory effect on the CNS to the degree that they reduce nervousness, excitability, and irritability without causing sleep. (p. 189)


Sedative-hypnotics Drugs that can act in the body either as sedatives or as hypnotics. (p. 189)


Sleep A transient, reversible, and periodic state of rest in which there is a decrease in physical activity and consciousness. (p. 189)


Sleep architecture The structure of the various elements involved in the sleep cycle, including normal and abnormal patterns of sleep. (p. 189)


Therapeutic index The ratio between the toxic and therapeutic concentrations of a drug. If the index is low, the difference between the therapeutic and toxic drug concentrations is small, and use of the drug is more hazardous. (p. 193)


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Anatomy, Physiology, and Pathophysiology Overview


Sedatives and hypnotics are drugs that have a calming effect or that depress the central nervous system (CNS). A drug is classified as either a sedative or a hypnotic drug depending on the degree to which it inhibits the transmission of nerve impulses to the CNS. Sedatives reduce nervousness, excitability, and irritability without causing sleep, but a sedative can become a hypnotic if it is given in large enough doses. Hypnotics cause sleep and have a much more potent effect on the CNS than do sedatives. Many drugs can act as either a sedative or a hypnotic, depending on dose and patient responsiveness, and for this reason are called sedative-hypnotics. Sedative-hypnotics can be classified chemically into three main groups: barbiturates, benzodiazepines, and miscellaneous drugs.


Physiology of Sleep


Sleep is defined as a transient, reversible, and periodic state of rest in which there is a decrease in physical activity and consciousness. Normal sleep is cyclic and repetitive, and a person’s responses to sensory stimuli are markedly reduced during sleep. During waking hours, the body is bombarded with stimuli that provoke the senses of sight, hearing, touch, smell, and taste. These stimuli elicit voluntary and involuntary movements or functions. During sleep, a person is no longer aware of the sensory stimuli within his or her immediate environment.


Sleep research involves study of the patterns of sleep, or what is sometimes referred to as sleep architecture. The architecture of sleep consists of two basic elements that occur cyclically: rapid eye movement (REM) sleep and non–rapid eye movement (non-REM) sleep. The normal cyclic progression of the stages of sleep is summarized in Table 12-1. Various sedative-hypnotic drugs affect different stages of the normal sleep pattern. Prolonged sedative-hypnotic use may reduce the cumulative amount of REM sleep; this is known as REM interference. This can result in daytime fatigue, because REM sleep provides a certain component of the “restfulness” of sleep. Upon discontinuance of a sedative-hypnotic drug, REM rebound can occur in which the patient has an abnormally large amount of REM sleep, often leading to frequent and vivid dreams. Abuse and misuse of sedative-hypnotic drugs is common and is discussed in Chapter 17.




Pharmacology Overview


Benzodiazepines and Miscellaneous Hypnotic Drugs


Historically, benzodiazepines were the most commonly prescribed sedative-hypnotic drugs; however, the nonbenzodiazepine drugs are now more frequently prescribed. Other drugs commonly used for sleep include the antihistamine diphenhydramine (see Chapter 36), trazodone, and amitriptyline (see Chapter 16). The benzodiazepines show favorable adverse effect profiles, efficacy, and safety when used appropriately. Benzodiazepines are classified as either sedative-hypnotics or anxiolytics depending on their primary usage. Anxiolytic drugs are used to reduce the intensity of feelings of anxiety. However, any of these drugs can function along a continuum as a sedative and/or hypnotic and/or anxiolytic depending on the dosage and patient sensitivity. See Chapter 16 for a further discussion of the anxiolytic use of benzodiazepines. There are five benzodiazepines commonly used as sedative-hypnotic drugs. In addition, there are several miscellaneous drugs that are used as hypnotics. They function much like benzodiazepines but are chemically distinct from them. All are listed in Table 12-2. Ramelteon is a hypnotic drug not related to any other hypnotics. It has a new mechanism of action and is profiled separately later in the chapter.



Mechanism of Action and Drug Effects


The sedative and hypnotic action of benzodiazepines is related to their ability to depress activity in the CNS. The specific areas that are affected include the hypothalamic, thalamic, and limbic systems of the brain. Although the mechanism of action is not certain, research suggests that there are specific receptors in the brain for benzodiazepines. These receptors are thought to be either gamma-aminobutyric acid (GABA) receptors or other adjacent receptors. GABA is the primary inhibitory neurotransmitter of the brain, and it serves to modulate CNS activity by inhibiting overstimulation. Like GABA itself, benzodiazepine activity appears to be related to their ability to inhibit stimulation of the brain. They have many favorable characteristics compared with the older drug class barbiturates (see the next section of this chapter). They do not suppress REM sleep to the same extent, nor do they induce hepatic microsomal enzyme activity as do the barbiturates. They are safe to administer to patients who are taking medications metabolized by this enzyme system.


Indications


Benzodiazepines have a variety of therapeutic applications. They are commonly used for sedation, relief of agitation or anxiety, treatment of anxiety-related depression, sleep induction, skeletal muscle relaxation, and treatment of acute seizure disorders. Benzodiazepines are often combined with anesthetics, analgesics, and neuromuscular blocking drugs in balanced anesthesia and also moderate sedation (see Chapter 11) for their amnesic properties to reduce memory of painful procedures. Finally, benzodiazepine receptors in the CNS are in the same area as those that play a role in alcohol addiction. Therefore, some benzodiazepines (e.g., diazepam, chlordiazepoxide) are used in the treatment and prevention of the symptoms of alcohol withdrawal (see Chapter 17). When benzodiazepines are used to treat insomnia, it is recommended that they be used short term if clinically feasible to avoid dependency. Two newer products that have been approved by the U.S. Food and Drug Administration (FDA) for long-term use for insomnia include eszopiclone (Lunesta) and an extended-release form of zolpidem (Ambien CR). These two drugs are classified as nonbenzodiazepines.


Contraindications


Contraindications to the use of benzodiazepines include known drug allergy, narrow-angle glaucoma, and pregnancy.


Adverse Effects


As a class, benzodiazepines have a relatively favorable adverse effect profile; however, they can be harmful if given in excessive doses or when mixed with alcohol. Adverse effects associated with their use usually involve the CNS. Commonly reported undesirable effects are headache, drowsiness, paradoxical excitement or nervousness, dizziness or vertigo, cognitive impairment, and lethargy. Benzodiazepines can create a significant fall hazard in elderly patients, and the lowest effective dose must be used in this patient population. Although these drugs have comparatively less intense effects on the normal sleep cycle, a “hangover” effect is sometimes reported (e.g., daytime sleepiness). Withdrawal symptoms such as rebound insomnia (i.e., greater insomnia than pretreatment) may occur with abrupt discontinuation.


Toxicity and Management of Overdose


An overdose of benzodiazepines may result in one or all of the following symptoms: somnolence, confusion, coma, and diminished reflexes. Overdose of benzodiazepines alone rarely results in hypotension and respiratory depression. These effects are more commonly seen when benzodiazepines are taken with other CNS depressants such as alcohol or barbiturates. The same holds true for their lethal effects. In the absence of the concurrent ingestion of alcohol or other CNS depressants, benzodiazepine overdose rarely results in death.


Treatment of benzodiazepine intoxication is generally symptomatic and supportive. Flumazenil, a benzodiazepine antidote, can be used to acutely reverse the sedative effects of benzodiazepines. It antagonizes the action of benzodiazepines on the CNS by directly competing with the benzodiazepine for binding at the receptors. Flumazenil is used in cases of oral overdose or excessive intravenous sedation. The dosage regimens to be followed for the reversal of conscious sedation or general anesthesia induced by benzodiazepines and the management of suspected overdose are summarized in Table 12-3.



Interactions


Potential drug interactions with the benzodiazepines are significant because of their intensity, particularly when they involve other CNS depressants (e.g., alcohol, opioids, muscle relaxants). These drugs result in further CNS depressant effects, including reduced blood pressure, reduced respiratory rate, sedation, confusion, and diminished reflexes. This and other major drug interactions are listed in Table 12-4. Herbal remedies that interact with the benzodiazepines include kava and valerian, which may also lead to further CNS depression. Food-drug interactions include interactions with grapefruit and grapefruit juice, which alter drug metabolism via inhibition of the cytochrome P-450 system and can result in prolonged effect, increased effect, and toxicity.



Dosages


For dosage information, see the table on p. 192.


Drug Profiles


Benzodiazepines and miscellaneous sedative-hypnotic drugs are prescription-only drugs, and they are designated as Schedule IV controlled substances. Uses for benzodiazepines can vary,





including treatment of insomnia, moderate sedation (see Chapter 11), muscle relaxation, anticonvulsant therapy (see Chapter 14), and anxiety relief (see Chapter 16). The miscellaneous drugs are normally used only for their hypnotic purposes to treat insomnia. Dosage information appears in the Dosages table on this page.


Benzodiazepines


diazepam


Diazepam (Valium) was the first clinically available benzodiazepine drug. It has varied uses, including treatment of anxiety,



procedural sedation and anesthesia adjunct, anticonvulsant therapy, and skeletal muscle relaxation following orthopedic injury or surgery. It is available in oral, rectal, and injectable forms.



midazolam


Midazolam (Versed) is most commonly used preoperatively and for moderate sedation (see Chapter 11). It is useful for this indication due to its ability to cause amnesia and anxiolysis (reduced anxiety) as well as sedation. This helps patients to feel less anxious about, and avoid remembering, uncomfortable medical procedures. The drug is normally given by injection in adults. However, a liquid oral dosage form is also available for children. See Chapter 11 for dosage information.


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May 9, 2017 | Posted by in NURSING | Comments Off on Central Nervous System Depressants and Muscle Relaxants

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