Sedative-Hypnotic Drugs

Introduction:

The name sedative-hypnotic indicates that it is able to cause sedation (with concomitant relief of anxiety) or to encourage sleep. Because there is considerable chemical variation within the group, this drug classification is based on clinical uses rather than on similarities in chemical structure. Anxiety states and sleep disorders are common problems, and sedative-hypnotics are widely prescribed drugs worldwide.

Basic Pharmacology of Sedative-Hypnotics

An effective sedative (anxiolytic) agent should reduce anxiety and exert a calming effect. The degree of central nervous system depression caused by a sedative should be the minimum consistent with therapeutic efficacy. 

A hypnotic drug should produce drowsiness and encourage the onset and maintenance of a state of sleep. Hypnotic effects involve more pronounced depression of the central nervous system than sedation, and this can be achieved with many drugs in this class simply by increasing the dose. 

Graded dose-dependent depression of central nervous system function is a characteristic of most sedative-hypnotics. However, individual drugs differ in the relationship between the dose and the degree of central nervous system depression. For e.g.

The linear slope for drug A is typical of many of the older sedative-hypnotics, including the barbiturates and alcohols. With such drugs, an increase in dose higher than that needed for hypnosis may lead to a state of general anesthesia. At still higher doses, these sedative-hypnotics may depress respiratory and vasomotor centers in the medulla, leading to coma and death. Deviations from a linear dose-response relationship, as shown for drug B, require proportionately greater dosage increments to achieve central nervous system depression more profound than hypnosis. This appears to be the case for benzodiazepines and for certain newer hypnotics that have a similar mechanism of action.

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