Freeincamsex Mechanism of action of sedating antihistamines

Sedatives encompass a wide variety of drugs with different mechanisms of action that can induce depression of the central nervous system (CNS).

In addition, most analgesic-hypnotic combination medications (“” preparations) contain diphenhydramine.Second-generation nonsedating antihistamine drugs are used primarily for treatment of seasonal, environmental, and other allergic reactions and are not used for the treatment of insomnia.-receptor blockade.Besides those two groups of drugs, other sedatives are also used for that purpose.Barbiturates are nonselective CNS depressants that used to be the mainstay of treatment to sedate patients or to induce and maintain sleep.In addition to this antihistamine effect, they can have parallel pharmacological properties, for example antimuscarinic and adrenolytic effects which must be considered.

It is usual to classify H1-antihistamines into two classes: old ones, called first-generation agents, which are sedating and recent ones, called second-generation agents which have slight or no sedating effects because they do not cross the blood-brain barrier.

First-generation agents include doxepin (discussed earlier under antidepressants), diphenhydramine, doxylamine, chlorpheniramine, hydroxyzine, meclizine, promethazine, and cyproheptadine.

Essentially all of the over-the-counter antihistamine drugs marketed for insomnia treatment include diphenhydramine, the prototype of this class, or doxylamine.

Doxepin has potent effects on H-adrenergic receptor antagonism (amitriptyline may be the worst in this regard).

Secondary amine TCAs (e.g., nortriptyline) are generally believed to be less likely to cause orthostatic hypotension than tertiary amine TCAs.

In modern medicine they have been largely replaced by the benzodiazepines, primarily because they can induce tolerance, physical dependence and serious withdrawal symptoms.