Hydroxyzine is an antihistamine drug, commonly prepared as the salt hydroxyzine HCl. As a chloride salt, the pharmaceutical is sold under multiple brand names, including Atarax and Tranquizine. Like many antihistamines, hydroxyzine HCl has a number of side effects that vary in severity from very mild to quite bothersome and potentially dangerous.
Chemical Composition
Hydroxyzine HCl is a large organic molecule, consisting of 21 carbon atoms, 27 hydrogen atoms, two nitrogen atoms, two oxygen atoms and a chlorine atom. According to the "CRC Handbook of Chemistry and Physics," its molecular weight is 374.9 g/mol.
Drowsiness
Drugs.com, an online compendium of information about pharmaceuticals and side effects, lists drowsiness as one of the most common patient complaints about hydroxyzine HCl. Feelings of lethargy and sleepiness are quite common to many antihistamines and are the result of drug interaction with the central nervous system. This mild nervous system depression typically disappears within a few days, but there have been some reports of motor activity disturbance in severe cases. Generally in the form of tremors or shaking of the hands and feet, these disturbances are the result of involuntary muscle contraction.
Dry Mouth
Hydroxyzine HCl's mechanism of action requires that it shut down a portion of the nervous system called the cholinergic system, which is involved in many functions, including movement and mucus secretion. By reducing overall mucus secretion and drying nasal and ocular tissues, hydroxyzine HCl reduces feelings of stuffiness, runny nose and runny or watery eyes. Unfortunately, this effect is not confined to the eyes and nose; the mucus-secreting membranes of the mouth are also affected, meaning that salivary secretion is significantly reduced. This can lead to feelings of dry mouth, and while this side effect is not at all dangerous, it can be irritating. Sipping water or noncaffeinated beverages may help relieve symptoms.
Allergic Reaction
As with most pharmaceuticals, hydroxyzine HCl can cause allergic reaction in rare cases. Such reactions can be quite mild, consisting only of a rash, itching or hives on the face or body. In rare cases, however, allergic reactions may be severe and involve swelling of the mouth, tongue and throat tissues. Such reactions make it difficult or impossible to breathe and are true medical emergencies. As severe allergic reactions progress, some patients experience sudden and catastrophic drops in blood pressure due to leaking of the blood plasma out of body capillaries---small blood vessels---and into the spaces between cells. Emergency treatment, generally including the stimulant hormone epinephrine, helps stop severe allergic reactions to hydroxyzine HCl.
References
- "CRC Handbook of Chemistry and Physics"; David Lide; 1974
- Drugs: Hydroxyzine Side Effects
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