Histamine antagonists or antihistamines are drugs that relieve allergy symptoms.<br><br>Histamine is a chemical used to identify and remove substances that trigger an allergic response. Â There are four histamine receptors (designated H<sub>1</sub>, H<sub>2</sub>, H<sub>3</sub>, H<sub>4</sub>). When histamine activates H<sub>1</sub> receptors, symptoms such as rashes, itching, watery eyes and trouble breathing may begin. <br><br>Antihistamines prevent histamine from stimulating the H<sub>1</sub> receptors located in the eyes, nose and throat to relieve swelling and stop leaking fluid. Â First generation antihistamines were non-selective for H<sub>1</sub> receptors and crossed into the brain resulting in drowsiness. Â Newer antihistamines are more selective, reducing this side effect.
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Frequently Asked Questions (FAQs) on Zyrtec: Oral tablet
They need to know if you have any of these conditions: -kidney disease -liver disease -an unusual or allergic reaction to cetirizine, hydroxyzine, other medicines, foods, dyes, or preservatives -pregnant or trying to get pregnant -breast-feeding
Take this medicine by mouth with a glass of water. Follow the directions on the prescription label. You can take this medicine with food or on an empty stomach. Take your medicine at regular times. Do not take more often than directed. You may need to take this medicine for several days before your symptoms improve.
Talk to your pediatrician regarding the use of this medicine in children. Special care may be needed. While this drug may be prescribed for children as young as 6 years of age for selected conditions, precautions do apply.
Visit your doctor or health care professional for regular checks on your health. Tell your doctor if your symptoms do not improve.
You may get drowsy or dizzy. Do not drive, use machinery, or do anything that needs mental alertness until you know how this medicine affects you. Do not stand or sit up quickly, especially if you are an older patient. This reduces the risk of dizzy or fainting spells.
Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water may help. Contact your doctor if the problem does not go away or is severe.
What side effects may I notice from receiving this medicine?
Side effects that you should report to your doctor or health care professional as soon as possible: -allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue -changes in vision or hearing -fast or irregular heartbeat -trouble passing urine or change in the amount of urine
Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome): -dizziness -dry mouth -irritability -sore throat -stomach pain -tiredness