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382 SECTION V Drugs That Act in the Central Nervous System

Coma The chemical structures of some older and less commonly
Drug A used sedative-hypnotics, including several barbiturates, are
shown in Figure 22–3. Glutethimide and meprobamate are of
Anesthesia
distinctive chemical structure but are practically equivalent to
CNS effects Hypnosis Drug B The sedative-hypnotic class also includes compounds of simpler
barbiturates in their pharmacologic effects. They are rarely used.
chemical structure, including ethanol (see Chapter 23) and

Sedation chloral hydrate.
Several drugs with novel chemical structures have been intro-
duced more recently for use in sleep disorders. Zolpidem, an
imidazopyridine; zaleplon, a pyrazolopyrimidine; and eszopi-
clone, a cyclopyrrolone (Figure 22–4), although structurally
Increasing dose unrelated to benzodiazepines, share a similar mechanism of action,
as described below. Eszopiclone is the (S) enantiomer of zopiclone,
FIGURE 22–1 Dose-response curves for two hypothetical
sedative-hypnotics. a hypnotic drug that has been available outside the United States
since 1989. Ramelteon and tasimelteon, melatonin receptor

C H
2 5
H CH 2 CH 2 N
H C O N CH 3 O C H
3
2 5
N 1 2 N N
3
4
9 N N N
5
8 O
7 6
F
Cl Cl Cl
Diazepam Chlordiazepoxide Flurazepam

O O O
H H H
N N OH N OH

N N N

Cl
Cl Cl Cl

Desmethyldiazepam Oxazepam Lorazepam

H C H C
3
3
O N N
H
N
N N N N
N
Cl N Cl N
Cl
NO 2

Nitrazepam Triazolam Alprazolam

FIGURE 22–2 Chemical structures of some benzodiazepines.