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17894396-Chapter14-Sedative-Hynotics - Chapter 14...

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Unformatted text preview: Chapter 14 Sedative-Hypnotic drugs [Definitions] Sedative-Hypnotics: Assignment of a drug to the sedative-hypnotic class indicates that its major therapeutic use is to cause sedation (with concomitant relief of anxiety) or to encourage sleep. [Definations] Sedation:An effective sedative agent should reduce anxiety and exert an effect with little or no effect on motor or mental functions. [Definitions] Hypnosis:A hypnotic drug should produce drowsiness and encourage the onset and maintenance of a state of sleep that as far as possible resembles the natural sleep state. can be achieved with most sedative drugs simply by increasing the dose. Figure 14-1 Dose-response curves for two hypothetical sedative-hypnotics [Classification] 1. Benzodiezepines 2. Barbiturates 3.Other agents:e.g.chloral hydrate Section 1 Benzodiazepines The most widely used SedativeHypnotics. They are more effective and safer than barbiturates. [Classification] Short-acting: The half-life is 2-4 hours, e.g. Triazolam. Intermediate-acting: The half-life is 5-10 hours, e.g. Chlordiazepoxide Long-acting: The half-life is 30-60 hours, e.g. diazepam and flurazepam. [Pharmacokinetics] Absorption and distribution 1. oral absorption are well , im. absorption are slow and unreliable; iv. absorption are rapidly 2. are highly lipid-soluble and are largely binding to plasma proteins 3. Removal from the brain to the other tissues throughout the body [Pharmacokinetics] Biotransformation 1. metabolized by the liver to compounds that are also active. 2. metabolites are excreted in the urine. [effects and uses] 1.Anti-anxiety at the lowest effective doses used for the relieving of anxiety states, including restlessness,worry,stress and phobia states .Chlordiazepoxide and diazepam are often used. 2. Sedation exert calming effects at relatively low doses. used to relieve the stress of patients. Diazepam can cause temporary loss of memory after iv. used for patients undergoing tracheoscopy and electric defibrillation before the treatment or examination. 3. Hypnosis rapid eye movement sleep natural sleep non-rapid eye movement sleep (includes slow-wave sleep) 3. Hypnosis Advantages: The latency of sleep onset is decreased (time to fall asleep); The duration of stage 2 NREM sleep is increased; The duration of REM sleep is decreased; The duration of stage 4 NREM slowwave sleep is decreased. Disadvantages A similar pattern of "REM rebound" can be detected following abrupt cessation of drug treatment with sedative-hypnotics, especially when drugs with short durations of action are used at high doses. The use of sedative-hypnotics for more than 12 weeks leads to some tolerance to their effects on sleep patterns. Effects and Uses 4.Anticonvulsant effects Inhibit the development and spread of epileptiform activity in the CNS and are useful in the treatment of convulsion and status epileptics. Clonazepam is useful in the chronic treatment of epilepsy, diazepam is the drug of first choice in terminating grand mal epileptic seizures and status epileptics. Effects and Uses 5.Relaxation of muscle inhibit polysynaptic reflexes and internuncial transmission (in CNS), and depress transmission at the skeletal neuromuscular junction, lead to muscle relaxation. Useful in the treatment of skeletal muscle spasms, multiple sclerosis and cerebral palsy. [Mechanism of action] GABA is the major inhibitory neurotransmitter in the central nervous system. GABAA receptor, which functions as a chloride ion channel, is activated by the inhibitory neurotransmitter GABA . Binding of GABA to its receptors may open chloride channels and facilitate Cl- entry into neurons. The influx of Cl- cause a small hyperpolarization that moves the postsynaptic potential and thus inhibits the formation of action potentials, which produces an inhibitory effect on neuronal conduction. Benzodiazepines bind to the GABAA receptor present in the CNS which promotes GABA binding to it's receptors , thus may increase the frequency of Cl- channel-opening and facilitate more Cl- entry into neurons that increase the efficiency of GABA synaptic inhibition. Adverse reactions 1.CNS depression dizziness, asthenia, drowsiness etc. 2.Tolerance and Dependence. Section 2 Barbiturates 1.Ultra-short-acting: 2.Short-acting: [Classification] Duration of action is about 30', e.g. thiopental. 2-3 hours, e.g. secobarbital. 3.Intermediate-acting: 3-6 hours,e.g. pentobarbital. 4.Long-acting: 6-8 hours, e.g. Phenobarbital. Pharmacokinetics Oral administration are absorbed rapidly. Duration of action depends on metabolic degradation, degree of lipid solubility and extent of binding to serum proteins. Lipid solubility plays a major role. Pharmacokinetics Enzyme induction:induce hepatic microsomal drug-metabolizing enzymes, especially phenobarbital. (1) leads to tolerance. (2) Diminishes the action of many drugs (e.g phenytoin) Pharmacokinetics excreted via kidney. Alkalinization of urine promotes excretion of babiturates. Mechanisms 1.GABA inhibition(duration of Clchannel opening) 2.interfere with sodium and potassium transport that leads to inhibition of the mesencephalic reticular activating system. [effects and uses] 1. Sedation and hypnosis The duration of sleep is increased and the time of inducing sleep is decreased. 2.Antiepileptism Phenobarbital is often used for epileptism in infant and children as a first choice drug. 3. Anesthesia Thiopental is used intravenously to induce anesthesia. [effects and uses] 4.decrease oxygen utilization by brain especially in anesthetic doses, significantly decrease oxygen utilization by brain, which may be of value in lessening cerebral edema caused by surgery or trauma and in protecting against cerebral infarction duration cerebral ischemia. Adverse reactions 1. CNS depressant effects decrease in REMS . dizziness for hours after waking, sedation and a 2. Dependence Physiology dependence Psychological dependence Adverse reactions 3.Poisoning An overdose can result in coma,severe respiratory depression. Alkalization of the urine often aids in the elimination of phenobarbital. Chloral hydrate a relatively safe hypnotic drug used mainly in children and the elderly usually administered by enema in children Paraldehyde It is used for patients with hepatic or renal failure because it is mainly eliminated via the lungs. ...
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