Over the course of the 20th century, several medicines with diverse structures were used as sedatives and hypnotics. In general, the pharmacological proper ties of these medicines resembled the barbiturates. They produced profound CNS depression, with little or no analgesia. Their therapeutic index was low and their abuse potential was high, similar to the barbiturates. Chloral hydrate (Noctec), ethchlorvynol (Placidyl), ethinamate (Valmid), glutethimide (Doriden), meprobamate (Miltown, Equanil), methyprylon (Noludar), and paraldehyde (Paral) belong in this class of seldom-used medicines that do not have a useful place in contemporary medical practice.
Despite the continued widespread use of antihistamines to treat insomnia, the Food and Drug Administration (FDA), noting the prominent sedative side effects encountered in the administration of antihistamines (including doxylamine, diphenhydramine, and pyrilamine), concluded that the antihistamines are not consistently effective in the treatment of sleep disorders. Tolerance rapidly develops to the sedating effects of these medicines, and the antihistamines can produce paradoxical stimulation. In addition, the antihistamine doses currently approved for the treatment of allergies are inadequate to induce sleep. Antihistamines used to treat sleep disorders can produce daytime sedation because of their relatively long half-lives (Charney et al., 2001).
The use of sedating antidepressants such as Desyrel (trazodone) and Elavil (amitriptyline) to treat insomnia at dose levels lower than are effective for the treatment of depression, such as the use of sedating antihistamines for this indication, is clinically problematic, since these agents may be both less effective and more likely to produce undesirable side effects (especially in producing daytime sedation) than the use of benzodiazepines in this indication (Mendelson et al., 2001).
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