Description
Antihistamines are used to relieve or prevent the symptoms of hay fever and other types of allergy. They work by preventing the effects of a substance called histamine, which is produced by the body. Histamine can cause itching, sneezing, runny nose, and watery eyes. Also, in some persons histamine can close up the bronchial tubes (air passages of the lungs) and make breathing difficult.

Some of the antihistamines are also used to prevent motion sickness, nausea, vomiting, and dizziness. In patients with Parkinson's disease, diphenhydramine may be used to decrease stiffness and tremors. Also, the syrup form of diphenhydramine is used to relieve the cough due to colds or hay fever. In addition, since antihistamines may cause drowsiness as a side effect, some of them may be used to help people go to sleep.

Hydroxyzine is used in the treatment of nervous and emotional conditions to help control anxiety. It can also be used to help control anxiety and produce sleep before surgery.

Some antihistamines are used in the treatment of chronic urticaria, which is a persistent hive-like rash.

Antihistamines may also be used for other conditions as determined by your doctor.

Some antihistamine preparations are available only with your doctor's prescription. Others are available without a prescription. However, your doctor may have special instructions on the proper dose of the medicine for your medical condition.

These medicines are available in the following dosage forms:

Oral
Azatadine
Tablets (U.S. and Canada)
Brompheniramine
Capsules (U.S.)
Elixir (U.S. and Canada)
Tablets (Canada)
Cetirizine
Syrup (U.S.)
Tablets (U.S. and Canada)
Chlorpheniramine
Extended-release capsules (U.S.)
Syrup (U.S. and Canada)
Tablets (U.S. and Canada)
Chewable tablets (U.S.)
Extended-release tablets (U.S. and Canada)
Clemastine
Syrup (U.S. and Canada)
Tablets (U.S. and Canada)
Cyproheptadine
Syrup (Canada)
Tablets (U.S. and Canada)
Desloratadine
Tablets (U.S. and Canada)
Dexchlorpheniramine
Syrup (U.S. and Canada)
Tablets (U.S. and Canada)
Extended-release tablets (U.S. and Canada)
Dimenhydrinate
Extended-release capsules (Canada)
Oral Solution (U.S. and Canada)
Syrup (U.S. and Canada)
Tablets (U.S. and Canada)
Chewable tablets (U.S. and Canada)
Diphenhydramine
Capsules (U.S. and Canada)
Elixir (U.S. and Canada)
Tablets (U.S.)
Doxylamine
Tablets (U.S.)
Fexofenadine
Tablets (U.S. and Canada)
Capsules (U.S. )
Hydroxyzine
Capsules (U.S. and Canada)
Oral suspension (U.S.)
Syrup (U.S. and Canada)
Tablets (U.S.)
Loratadine
Syrup (U.S. and Canada)
Tablets (U.S. and Canada)
Phenindamine
Tablets (U.S.)
Parenteral
Brompheniramine
Injection (U.S.)
Chlorpheniramine
Injection (U.S. and Canada)
Dimenhydrinate
Injection (U.S. and Canada)
Diphenhydramine
Injection (U.S. and Canada)
Hydroxyzine
Injection (U.S. and Canada)
Rectal
Dimenhydrinate
Suppositories (Canada)

Proper Use of This Medicine
Antihistamines are used to relieve or prevent the symptoms of your medical problem. Take them only as directed. Do not take more of them and do not take them more often than recommended on the label, unless otherwise directed by your doctor. To do so may increase the chance of side effects.

Dosing - The dose of an antihistamine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of antihistamines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules or tablets or teaspoonfuls of liquid that you take or the number of suppositories you use depends on the strength of the medicine. Also, the number of doses you take each day and the time between doses depends on whether you are taking a short-acting or long-acting form of antihistamine.

For use as an antihistamine:
For azatadine
For oral dosage form (tablets):
Adults: 1 to 2 milligrams (mg) every eight to twelve hours as needed.
Children younger than 12 years of age: Use and dose must be determined by your doctor.
Children 12 years of age and older: 0.5 mg to 1 mg two times a day as needed.
For brompheniramine
For regular (short-acting) oral dosage forms (capsules, tablets, or liquid):
Adults and teenagers: 4 milligrams (mg) every four to six hours as needed.
Children 2 to 6 years of age: 1 mg every four to six hours as needed.
Children 6 to 12 years of age: 2 mg every four to six hours as needed.
For injection dosage form:
Adults and teenagers: 10 milligrams (mg) injected into a muscle, under the skin, or into a vein every eight to twelve hours.
Children younger than 12 years of age: 0.125 mg per kilogram (0.06 mg per pound) of body weight injected into a muscle, under the skin, or into a vein three or four times a day as needed.
For cetirizine
For oral dosage forms (syrup and tablets):
Adults: 5 to 10 milligrams (mg) once a day.
Children younger than 2 years of age: Use and dose must be determined by your doctor.
Children 2 to 6 years of age: 2.5 mg once a day, up to a maximum of 5 mg once a day or 2.5 mg twice a day.
Children 6 years of age and older: 5 to 10 mg once a day.
For chlorpheniramine
For regular (short-acting) oral dosage forms (tablets or liquid):
Adults and teenagers: 4 milligrams (mg) every four to six hours as needed.
Children younger than 6 years of age: Use and dose must be determined by your doctor.
Children 6 to 12 years of age: 2 mg three or four times a day as needed.
For long-acting oral dosage forms (capsules or tablets):
Adults: 8 or 12 milligrams (mg) every eight to twelve hours as needed.
Children younger than 12 years of age: Use and dose must be determined by your doctor.
Children 12 years of age and older: 8 mg every twelve hours as needed.
For injection dosage form:
Adults: 5 to 40 milligrams (mg) injected into a muscle, into a vein, or under the skin.
Children: 0.0875 mg per kilogram (0.04 mg per pound) of body weight injected under the skin every six hours as needed.
For clemastine
For oral dosage forms (tablets or liquid):
Adults and teenagers: 1.34 milligrams (mg) two times a day or 2.68 mg one to three times a day as needed.
Children younger than 6 years of age: Use and dose must be determined by your doctor.
Children 6 to 12 years of age: 0.67 to 1.34 mg two times a day.
For cyproheptadine
For oral dosage forms (tablets or liquid):
Adults and children 14 years of age and older: 4 milligrams (mg) every eight hours. The doctor may increase the dose if needed.
Children 2 to 6 years of age: 2 mg every eight to twelve hours as needed.
Children 6 to 14 years of age: 4 mg every eight to twelve hours as needed.
For desloratadine
For oral dosage form (tablets):
Adults and children 12 years of age and older: 5 milligrams (mg) once a day.
Children younger than 12 years of age: Use and dose must be determined by your doctor.
For dexchlorpheniramine
For regular (short-acting) oral dosage forms (tablets or liquid):
Adults and teenagers: 2 milligrams (mg) every four to six hours as needed.
Children 2 to 5 years of age: 0.5 mg every four to six hours as needed.
Children 5 to 12 years of age: 1 mg every four to six hours as needed.
For long-acting oral dosage form (tablets):
Adults: 4 or 6 milligrams (mg) every eight to twelve hours as needed.
Children: Use and dose must be determined by your doctor.

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