Drugs » Sedatives - Hypnotics

Sedatives - Hypnotics

Sedative: A drug that subdues excitement and calms the subject without inducing sleep, though drowsiness may be produced.

Hypnotic: A drug that induces and/ or maintains sleep, similar to normal arousable sleep.

Both sedatives and hypnotics are more or less general CNS depressants. A hypnotic at lower dose may at as a sedative. Thus, sedation → hypnotic → general anaesthesia may be regarded as increasing grades of CNS depression. The most important use of this class of drug is treatment of insomnia.

Classification

1. Barbiturate

2. Benzodiazepines

3. Newer nonbenzodiazepine hypnotics

(Older sedative- hypnotics are chloral hydrate, Triclophos, Meprobamate.)

Barbiturates
Except for phenobarbitone in epilepsy and thiopentone in anaesthesia, barbiturates are seldom used now.

As hypnotic and anxiolytic they have been superseded by benzodiazepines. They are occasionally employed as adjuvants in psychosomatic disorders. The enzyme inducing property of phenabarbitone can be utilized to hasten clearance of congenital nonhaemolytic jaundice and kernicterus.

Dosage:
Phenobarbitone 30-60mg OD-TDS, 100-200mg I.M/I.V.

Benzodiazepines
Chlordiazepoxide and diazepam were introduced around 1960 as antianxiety drugs. Since then this class has proliferated and has gained popularity over barbiturates both as hypnotic and sedative, because

1. Benzodiazepines (BZD) have high therapeutic index.
2. Hypnotic doses do not affect respiration or cardiovascular functions.
3. BZD have practically no action on other body systems.
4. BZD cause less distortion of sleep architecture.
5. BZDs do not alter disposition of other drugs by microsomal enzyme induction.
6. They have lower abuse liability: tolerance mild, psychological and physical dependence and withdrawal syndrome are less marked.
7. A specific BZD antagonist Flumazenil has been developed which can be used in case of poisoning.
8. In contrast to barbiturates they are not general depressants, but exert relatively selective anxiolytic, hypnotic, muscle relaxant and anti convulsant effects.
9. BZDs produce centrally mediated skeletal muscle relaxation without impairing voluntary activity. Clonazepam and diazepam have more marked muscle relaxant property.
10. Clonazepam, diazepam, nitrazepam and flurazepam have more prominent anti convulsant activity than other BZDs. However, their utility in epilepsy is limited by development of tolerance to the anticonvulsant action.

Adverse Effects:
BZDs are relatively safe drugs. Side effects of hypnotic doses are

• dizziness
• vertigo
• ataxia
• disorientation
• amnesia
• prolongation of reaction time
• impairment of psychomotor skills