Brand Names

Category

• Antianxiety agent--Hydroxyzine
• Antiasthmatic--Astemizole; Cetirizine; Loratadine; Terfenadine
• Antidyskinetic--Diphenhydramine
• Antiemetic--Dimenhydrinate; Diphenhydramine; Hydroxyzine (parenteral)
• Antihistaminic, H ₁ -receptor--Astemizole; Azatadine; Brompheniramine; Cetirizine; Chlorpheniramine; Clemastine; Cyproheptadine; Dexchlorpheniramine; Dimenhydrinate; Diphenhydramine; Doxylamine; Hydroxyzine; Loratadine; Phenindamine; Terfenadine; Tripelennamine
• Antitussive--Diphenhydramine Syrup
• Antivertigo agent--Dimenhydrinate; Diphenhydramine
• Appetite stimulant--Cyproheptadine
• Sedative-hypnotic--Diphenhydramine; Doxylamine; Hydroxyzine
• Vascular headache suppressant--Cyproheptadine

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.

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
• Astemizole
  • Oral suspension (Germany and United Kingdom)
  • Tablets (Germany and United Kingdom)
• 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)
• 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.)
• 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.)
• Terfenadine
  • Oral suspension (Australia and United Kingdom)
  • Tablets (Australia and United Kingdom)
• Tripelennamine
  • Elixir (U.S.)
  • Tablets (U.S. and Canada)
  • Extended-release 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)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For antihistamines, the following should be considered:

Allergies--Tell your doctor if you have ever had any unusual or allergic reaction to antihistamines. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Diet--Make certain your health care professional knows if you are on a low-sodium, low-sugar, or any other special diet. Most medicines contain more than their active ingredient, and many liquid medicines contain alcohol.

It is very important that you do not take astemizole (e.g., Hismanal) or terfenadine (e.g., Seldane) with grapefruit juice . Studies have shown that taking astemizole or terfenadine and grapefruit juice may cause heart rhythm problems.

Pregnancy--Hydroxyzine is not recommended for use in the first months of pregnancy since it has been shown to cause birth defects in animal studies when given in doses many times higher than the usual human dose. Be sure you have discussed this with your doctor.

Astemizole and terfenadine have not been studied in pregnant women. However, studies in animals have shown that these medicines cause birth defects or other problems when given in doses higher than the usual human dose. Before taking this medicine, make sure your doctor knows if you are pregnant or if you may become pregnant.

Azatadine, brompheniramine, cetirizine, chlorpheniramine, clemastine, cyproheptadine, dexchlorpheniramine, dimenhydrinate, diphenhydramine, doxylamine, loratadine, and tripelennamine have not been studied in pregnant women. However, these medicines have not been shown to cause birth defects or other problems in animal studies.

Breast-feeding--Small amounts of antihistamines pass into the breast milk. Use is not recommended since babies are more susceptible to the side effects of antihistamines, such as unusual excitement or irritability. Also, since these medicines tend to decrease the secretions of the body, it is possible that the flow of breast milk may be reduced in some patients. It is not known yet whether astemizole, cetirizine, loratadine, or terfenadine cause these same side effects.

Children--Serious side effects, such as convulsions (seizures), are more likely to occur in younger patients and would be of greater risk to infants than to older children or adults. In general, children are more sensitive to the effects of antihistamines. Also, nightmares or unusual excitement, nervousness, restlessness, or irritability may be more likely to occur in children.

Older adults--Elderly patients are usually more sensitive to the effects of antihistamines. Confusion; difficult or painful urination; dizziness; drowsiness; feeling faint; or dryness of mouth, nose, or throat may be more likely to occur in elderly patients. Also, nightmares or unusual excitement, nervousness, restlessness, or irritability may be more likely to occur in elderly patients.

Other medicines--Although certain medicines should not be used together at all, in other cases different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking antihistamines it is especially important that your health care professional knows if you are taking any of the following:

• Anticholinergics (medicine for abdominal or stomach spasms or cramps)--Side effects, such as dryness of mouth, of antihistamines or anticholinergics may be more likely to occur

• Clarithromycin (e.g., Biaxin) or
• Erythromycin (e.g., E-Mycin) or
• Itraconazole (e.g., Sporanox) or
• Ketoconazole (e.g., Nizoral) or
• Troleandomycin--Use of these medicines with astemizole or terfenadine may cause heart problems, such as an irregular heartbeat; these medicines should not be used together

• Bepridil (e.g., Vascor) or
• Disopyramide (e.g., Norpace) or
• Maprotiline (e.g., Ludiomil) or
• Phenothiazines (acetophenazine [e.g., Tindal], chlorpromazine [e.g., Thorazine], fluphenazine [e.g., Prolixin], mesoridazine [e.g., Serentil], perphenazine [e.g., Trilafon], prochlorperazine [e.g., Compazine], promazine [e.g., Sparine], promethazine [e.g., Phenergan], thioridazine [e.g. Mellaril], trifluoperazine [e.g., Stelazine], triflupromazine [e.g., Vesprin], trimeprazine [e.g., Temaril]) or
• Pimozide (e.g., Orap) or
• Procainamide (e.g., Pronestyl) or
• Quinidine (e.g., Quinaglute Dura-tabs) or
• Tricyclic antidepressants (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Pertofrane], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil])--Use of these medicines with astemizole or terfenadine may increase the risk of heart rhythm problems

• Central nervous system (CNS) depressants (medicines that cause drowsiness)--Effects, such as drowsiness, of CNS depressants or antihistamines may be worsened; also, taking maprotiline or tricyclic antidepressants may cause some side effects of either of these medicines, such as dryness of mouth, to become more severe

• Cisapride (e.g., Propulsid) or
• HIV-protease inhibitors (indinavir [e.g., Crixivan], nelfinavir [e.g., Viracept], ritonavir [e.g., Norvir], saquinavir [e.g., Fortovase, Invirase]) or
• Mibefradil (e.g., Posicor) or
• Serotonin reuptake inhibitors (fluoxetine [e.g., Prozac], fluvoxamine [e.g., Luvox], nefazodone [e.g., Serzone], paroxetine [e.g., Paxil], sertraline [e.g., Zoloft]) or
• Sparfloxacin (e.g., Zagam) or
• Zileuton (e.g., Zyflo)--Use of these medicines with astemizole or terfenadine may cause heart problems; these medicines should not be used with astemizole or terfenadine

• Monoamine oxidase (MAO) inhibitors (furazolidone [e.g., Furoxone], isocarboxazid [e.g., Marplan], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], selegiline [e.g., Eldepryl], tranylcypromine [e.g., Parnate])--If you are now taking, or have taken within the past 2 weeks, any of the MAO inhibitors, the side effects of the antihistamines, such as drowsiness and dryness of mouth, may become more severe; these medicines should not be used together

• Quinine--Use of this medicine with astemizole may cause heart problems, such as irregular heartbeat; these medicines should not be used together

Other medical problems--The presence of other medical problems may affect the use of antihistamines. Make sure you tell your doctor if you have any other medical problems, especially:

• Enlarged prostate or
• Urinary tract blockage or difficult urination--Antihistamines may make urinary problems worse

• Glaucoma--These medicines may cause a slight increase in inner eye pressure that may make the condition worse

• Heart rhythm problems (history of) or
• Intestinal obstruction
• Low potassium blood levels--Use of astemizole or terfenadine can cause serious heart rhythm problems

• Liver disease--Higher blood levels of astemizole or terfenadine may result, which may increase the chance of heart problems

• Stomach ulcer

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 astemizole
    • For oral dosage forms (tablets or liquid):
      • Adults and teenagers: 10 milligrams (mg) once a day.
      • Children younger than 6 years of age: 0.2 mg per kilogram (kg) (0.1 mg per pound) of body weight once a day.
      • Children 6 to 12 years of age: 5 mg once a day.
  • 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 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.
  • For diphenhydramine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults and teenagers: 25 to 50 milligrams (mg) every four to six hours as needed.
      • Children younger than 6 years of age: 6.25 to 12.5 mg every four to six hours.
      • Children 6 to 12 years of age: 12.5 to 25 mg every four to six hours.
    • For injection dosage form:
      • Adults: 10 to 50 milligrams (mg) injected into a muscle or into a vein.
      • Children: 1.25 mg per kg (0.6 mg per pound) of body weight injected into a muscle four times a day.
  • For doxylamine
    • For oral dosage form (tablets):
      • Adults and teenagers: 12.5 to 25 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: 6.25 to 12.5 mg every four to six hours as needed.
  • For hydroxyzine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults and teenagers: 25 to 100 milligrams (mg) three or four times a day as needed.
      • Children younger than 12 years of age: 0.5 mg per kg (0.2 mg per pound) of body weight every six hours as needed.
  • For loratadine
    • For oral dosage forms (tablets or liquid):
      • Adults and children 6 years of age and older: 10 milligrams (mg) once a day.
      • Children 2 to 5 years of age: 5 mg once a day.
  • For phenindamine
    • For oral dosage form (tablets):
      • Adults and teenagers: 25 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: 12.5 mg every four to six hours as needed.
  • For terfenadine
    • For oral dosage forms (tablets or liquid):
      • Adults and teenagers: 60 milligrams (mg) every twelve hours.
      • Children 3 to 6 years of age: 15 mg every twelve hours as needed.
      • Children 7 to 12 years of age: 30 mg every twelve hours as needed.
  • For tripelennamine
    • For regular (short-acting) oral dosage forms (tablets or liquid):
      • Adults: 25 to 50 milligrams (mg) every four to six hours as needed.
      • Children: 1.25 mg per kilogram (kg) (0.6 mg per pound) of body weight every six hours as needed.
    • For long-acting oral dosage form (tablets):
      • Adults: 100 milligrams (mg) every eight to twelve hours as needed.
      • Children: Use and dose must be determined by your doctor.
• For nausea, vomiting, and vertigo (only dimenhydrinate and diphenhydramine are used for vertigo):
  • For dimenhydrinate
    • For regular (short-acting) oral dosage forms (tablets or liquid):
      • Adults and teenagers: 50 to 100 milligrams (mg) every four to six hours as needed.
      • Children 2 to 6 years of age: 12.5 to 25 mg every six to eight hours as needed.
      • Children 6 to 12 years of age: 25 to 50 mg every six to eight hours as needed.
    • For long-acting oral dosage form (capsules):
      • Adults: 1 capsule (contains 25 milligrams [mg] for immediate action and 50 mg for long action) every twelve hours.
      • Children: Use and dose must be determined by your doctor.
    • For injection dosage form:
      • Adults: 50 milligrams (mg) injected into a muscle or into a vein every four hours as needed.
      • Children: 1.25 mg per kg (0.6 mg per pound) of body weight injected into a muscle or into a vein every six hours as needed.
    • For suppository dosage form:
      • Adults: 50 to 100 milligrams (mg) inserted into the rectum every six to eight hours as needed.
      • Children younger than 6 years of age: Use and dose must be determined by your doctor.
      • Children 6 to 8 years of age: 12.5 to 25 mg inserted into the rectum every eight to twelve hours as needed.
      • Children 8 to 12 years of age: 25 to 50 mg inserted into the rectum every eight to twelve hours as needed.
      • Children 12 years of age and older: 50 mg inserted into the rectum every eight to twelve hours as needed.
  • For diphenhydramine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 25 to 50 milligrams (mg) every four to six hours as needed.
      • Children: 1 to 1.5 mg per kg (0.45 to 0.7 mg per pound) of body weight every four to six hours as needed.
    • For injection dosage form:
      • Adults: 10 milligrams (mg) injected into a muscle or into a vein. Dose may be increased to 25 to 50 mg every two to three hours.
      • Children: 1 to 1.5 mg per kg (0.45 to 0.68 mg per pound) of body weight injected into a muscle every six hours.
  • For hydroxyzine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 25 to 100 milligrams (mg) three or four times a day as needed.
      • Children younger than 6 years of age: 12.5 mg every six hours as needed.
      • Children 6 years of age and older: 12.5 to 25 mg every six hours as needed.
      
      For injection dosage form:
      • Adults: 25 to 100 milligrams (mg) injected into a muscle.
      • Children: 1 mg per kg (0.45 mg per pound) of body weight injected into a muscle.
• For Parkinson's disease:
  • For diphenhydramine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 25 milligrams (mg) three times a day when starting treatment. Your doctor may increase the dose gradually later if needed.
    • For injection dosage form:
      • Adults: 10 to 50 milligrams (mg) injected into a muscle or into a vein.
      • Children: 1.25 mg per kg (0.6 mg per pound) of body weight four times a day injected into a muscle.
• For use as a sedative (to help sleep):
  • For diphenhydramine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 50 milligrams (mg) twenty to thirty minutes before bedtime if needed.
  • For doxylamine
    • For oral dosage form (tablets):
      • Adults: 25 milligrams (mg) thirty minutes before bedtime if needed.
      • Children: Use and dose must be determined by your doctor.
  • For hydroxyzine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 50 to 100 milligrams (mg).
      • Children: 0.6 mg per kg (0.3 mg per pound) of body weight.
    • For injection dosage form:
      • Adults: 50 milligrams (mg) injected into a muscle.
• For anxiety:
  • For hydroxyzine
    • For oral dosage forms (capsules, tablets, or liquid):
      • Adults: 50 to 100 milligrams (mg).
      • Children: 0.6 mg per kilogram (0.3 mg per pound) of body weight.
    • For injection dosage form:
      • Adults: 50 to 100 milligrams (mg) injected into a muscle every four to six hours as needed.
      • Children: 1 mg per kilogram (0.45 mg per pound) of body weight injected into a muscle.

Missed dose--If you are taking this medicine regularly and you miss a dose, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

For patients taking this medicine by mouth:

• Antihistamines can be taken with food or a glass of water or milk to lessen stomach irritation if necessary. However, food may change the amount of astemizole that is absorbed. For this reason, astemizole should be taken on an empty stomach.
• If you are taking the extended-release tablet form of this medicine, swallow the tablets whole. Do not break, crush, or chew before swallowing.

For patients taking dimenhydrinate or diphenhydramine for motion sickness:

• Take this medicine at least 30 minutes or, even better, 1 to 2 hours before you begin to travel.

For patients using the suppository form of this medicine:

• To insert suppository: First remove the foil wrapper and moisten the suppository with cold water. Lie down on your side and use your finger to push the suppository well up into the rectum. If the suppository is too soft to insert, chill the suppository in the refrigerator for 30 minutes or run cold water over it before removing the foil wrapper.

For patients using the injection form of this medicine :

• If you will be giving yourself the injections, make sure you understand exactly how to give them. If you have any questions about this, check with your health care professional.

Storage--To store this medicine:

• Keep out of the reach of children, since overdose may be very dangerous in children.
• Store away from heat and direct light.
• Do not store the capsule or tablet form of this medicine in the bathroom medicine cabinet, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the liquid form of this medicine from freezing.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

Before you have any skin tests for allergies, tell the doctor in charge that you are taking this medicine. The results of the test may be affected by this medicine.

When taking antihistamines on a regular basis, make sure your doctor knows if you are taking large amounts of aspirin at the same time (as for arthritis or rheumatism). Effects of too much aspirin, such as ringing in the ears, may be covered up by the antihistamine.

Astemizole and terfenadine should not be taken with clarithromycin (e.g., Biaxin), erythromycin (e.g., E-Mycin), itraconazole (e.g., Sporanox), ketoconazole (e.g., Nizoral), mibefradil (e.g., Posicor), or troleandomycin . Using these medicines together may increase the risk of serious side effects affecting the heart.

Antihistamines will add to the effects of alcohol and other CNS depressants (medicines that slow down the nervous system, possibly causing drowsiness). Some examples of CNS depressants are sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine .

This medicine may cause some people to become drowsy or less alert than they are normally. Even if taken at bedtime, it may cause some people to feel drowsy or less alert on arising. Some antihistamines are more likely to cause drowsiness than others. Drowsiness is less likely with cetirizine, and rare with astemizole, loratadine, and terfenadine. Make sure you know how you react to the antihistamine you are taking before you drive, use machines, or do anything else that could be dangerous if you are not alert .

Antihistamines may cause dryness of the mouth, nose, and throat. Some antihistamines are more likely to cause dryness of the mouth than others (astemizole and terfenadine, for example, more commonly produce this effect). For temporary relief of mouth dryness, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

For patients using dimenhydrinate, diphenhydramine, or hydroxyzine:

• This medicine controls nausea and vomiting. For this reason, it may cover up the signs of overdose caused by other medicines or the symptoms of appendicitis. This will make it difficult for your doctor to diagnose these conditions. Make sure your doctor knows that you are taking this medicine if you have other symptoms of appendicitis such as stomach or lower abdominal pain, cramping, or soreness. Also, if you think you may have taken an overdose of any medicine, tell your doctor that you are taking this medicine.

For patients using diphenhydramine or doxylamine as a sleeping aid:

• If you are already taking a sedative or tranquilizer, do not take this medicine without consulting your doctor first.

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if the following side effect occurs:

Less common or rare--with high doses of astemizole or terfenadine; less frequent or rare with azatadine, cetirizine, clemastine, cyproheptadine, dexchlorpheniramine, diphenhydramine, or loratadine

Fast or irregular heartbeat; fever; abdominal or stomach pain; burning; chills; clay-colored stools or dark urine; cough; diarrhea; difficulty swallowing; dizziness; fast heartbeat; fever; headache; hives; itching; prickly sensations; puffiness or swelling of the eyelids or around the eyes, face, lips or tongue; seizures; shortness of breath; skin rash; tightness in chest; tingling; unusual tiredness or weakness; wheezing

Also, check with your doctor as soon as possible if any of the following side effects occur:

Less common or rare

Sore throat; unusual bleeding or bruising; unusual tiredness or weakness

Symptoms of overdose

Clumsiness or unsteadiness; convulsions (seizures); drowsiness (severe); dryness of mouth, nose, or throat (severe); feeling faint; flushing or redness of face; hallucinations (seeing, hearing, or feeling things that are not there); shortness of breath or troubled breathing; trouble in sleeping

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your health care professional if any of the following side effects continue or are bothersome:

More common

Drowsiness; dry mouth, nose, or throat; gastrointestinal upset, stomach pain, or nausea; increased appetite and weight gain; thickening of mucus

Less common or rare

Blurred vision or any change in vision; clumsiness or unsteadiness; confusion (not with diphenhydramine); constipation; diarrhea; difficult or painful urination; dizziness (not with brompheniramine, hydroxyzine, or tripelennamine; drowsiness (with high doses of astemizole, loratadine, and terfenadine; dryness of mouth, nose, or throat; early menstruation; fast heartbeat; fatigue; gastrointestinal upset, stomach pain or nausea; increased appetite and weight gain; increased sensitivity of skin to sun; increased sweating; loss of appetite; nightmares (not with azatadine, chlorpheniramine, cyproheptadine, hydroxyzine, or loratadine); ringing or buzzing in ears; skin rash; thickening of mucus; tremor; unusual excitement, nervousness, restlessness, or irritability; vomiting

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your health care professional.

Additional Information

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although this use is not included in product labeling, astemizole, cetirizine, loratadine, and terfenadine are used in certain patients with asthma together with asthma medicines. The antihistamine is used before and during exposure to substances that cause reactions, to prevent or reduce bronchospasm (wheezing or difficulty in breathing).

Cyproheptadine is used as an appetite stimulant, in adults and children

Cyproheptadine is used for treatment of vascular headaches.

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for this use.

Revised: 11/10/2000

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