Mechanism of action of sedating antihistamines

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Pregnancy category varies from A (controlled human studies have failed to demonstrate a risk to the fetus) through D (there is positive evidence of human fetal risk, use only in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective.which affect muscarinic receptors, such as scopolamine, increase motion tolerance.Clonazepam (Klonopin), is as effective a vestibular suppressant as lorazepam (Ganaca et al, 2002).The author prefers to avoid use of alprazolam (Xanax) for vestibular suppression, because of the potential for a difficult withdrawal syndrome.Relatively new are the 5HT3 agents (Zofran, Kytril).In theory, these agents might not be ideal for emesis related to vestibular imbalance.H3 receptor agonists appear to cause the same result as blockade of H2 receptors.Most antihistamines also have calcium channel blocking effect (according to Timmerman, 1994).

Injectables are used in the emergency room or inpatient settings. Some antihistamines commonly used as vestibular suppressants have significant antiemetic properties (e.g. When an oral agent is appropriate, this agent is generally the first to be used, because it rarely causes adverse effects any more severe than drowsiness.

Diphenidol (Vontrol), is also an anticholinergic, although little used in the US.

There are also some reports of scopolamine inducing migraine, as well as a withdrawall syndrome.

Anticholinergics also affect compensation, producing a reversible overcompensation if administered after compensation has been attained to a vestibular imbalance (Zee, 1988).

These drugs are often available OTC, or "over the counter". The antihistamine component has side effects of sleepiness and long term weight gain (see below).

All anticholinergics used in the management of vertigo have prominent side effects of dry mouth, dilated pupils, and sedation.

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