Histamine receptor antagonists anticholinergic effects

In anesthesia drugs from several groups are used as premedication. Pre-anesthetic medication can decrease the anesthetic doses which otherwise would be required to induce anesthesia and so decrease the risk for adverse effects. Pre-anesthetic medication will increase the rate of induction of anesthesia and can reduce pre-operative pain and anxiety. Drugs include benzodiazepines for sedation and their muscle relaxant properties, opiates for pain relieve and anticholinergics or histamine Hi receptor antagonists against nausea and vomiting. Neuroleptics are also used as premedication for their antiemetic effects. 

Histamine-1 receptor antagonists (e.g., diphenhydramine) and antidepressants with high histamine-1 blockade (e.g., doxepin and amitriptyline) have been used for acute sleep disturbances but may cause anticholinergic side effects, daytime sedation, and weight gain. Trazodone, a serotonin-2A and ai -adrenergic antagonist, has sedative properties at lower doses and may be useful to promote sleep. The chronic use of benzodiazepines is not recommended for insomnia... 

Histamine Hj-receptor antagonists are primarily useful for motion sickness and postoperative emesis. They act on vestibular afferents and within the brain stem. Cyclizine, hydroxyzine, promethazine, and diphenhydramine are examples of this class of agents. Cyclizine has additional anticholinergic effects that may be useful for patients with abdominal cancer. 

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