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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.
    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.
    It is very important that you read and understand the following information. If any of it causes you special concern, check with your doctor or pharmacist. Also, if you have any questions or if you want more information about this medicine or your medical problem, ask your doctor, nurse, or pharmacist.

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 doctor and pharmacist if you are allergic to any other substances, such as foods, preservatives, or dyes.
    Diet -- Make certain your doctor and pharmacist know 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.
    Pregnancy -- Most antihistamines have not been studied in pregnant women. Although these antihistamines have not been shown to cause problems in humans, studies in animals have shown that some other antihistamines, such as meclizine (e.g., Antivert) and cyclizine (e.g., Marezine), may cause birth defects.
    Also, studies in animals have shown that terfenadine, when given in doses several times the human dose, lowers the birth weight and increases the risk of death of the offspring.
    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 up to many times the usual human dose. Be sure you have discussed this with your doctor.
    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, loratadine, and terfenadine cause these same side effects.

Age Groups

    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:
    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 Therapy

    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:
    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 doctor and pharmacist know 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
• Central nervous system (CNS) depressants -- 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
• Erythromycin (e.g., E-Mycin) or
• Itraconazole (e.g., Sporanox) or
• Ketoconazole (e.g., Nizoral) -- Use of these medicines with astemizole and terfenadine may cause heart problems, such as an irregular heartbeat; these medicines should not be used together
• Monoamine oxidase (MAO) inhibitors (furazolidone [e.g., Furoxone], isocarboxazid [e.g., Marplan], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], 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 may become more severe; 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
• Liver disease -- Higher blood levels of astemizole or terfenadine may result, which may increase the chance of heart problems

    Before you begin using any new medicine (prescription or nonprescription) or if you develop any new medical problem while you are using this medicine, check with your doctor, nurse, or pharmacist.

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.
    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.

Dosing

    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.
• 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 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 doctor, nurse, or pharmacist.

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 in arthritis or rheumatism). Effects of too much aspirin, such as ringing in the ears, may be covered up by the antihistamine.
    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 (astemizole, loratadine, and terfenadine, for example, rarely produce this effect). 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, loratadine, and terfenadine, for example, rarely 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 only
        Fast or irregular heartbeat
    Also, check with your doctor as soon as possible if any of the following side effects occur:
    Less common or rare
        Sore throat and fever; 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 doctor or pharmacist if any of the following side effects continue or are bothersome:
    More common -- rare with astemizole, loratadine, and terfenadine; less common with cetirizine
        Drowsiness; thickening of mucus
    Less common or rare
        Blurred vision or any change in vision; confusion; difficult or painful urination; dizziness; dryness of mouth, nose, or throat; fast heartbeat; increased sensitivity of skin to sun; increased sweating; loss of appetite (increased appetite with astemizole and cyproheptadine); nightmares; ringing or buzzing in ears; skin rash; stomach upset or stomach pain (more common with pyrilamine and tripelennamine); unusual excitement, nervousness, restlessness, or irritability; weight gain (with astemizole and cyproheptadine only)

    Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor or pharmacist.

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

*This information is reproduced from the Mayo Clinic Family Pharmacist v 2.0
Copyright 1994-1995 IVI Publishing Inc.

This information may not be complete and/or up to date.  Please do not use this as any sort of authoritative text for this drug.  Please consult with a physician before taking this or any drug.  This is presented only for reference usage within this site.