Health Guide
Drug Guide

Antihistamine (Oral route, parenteral route, rectal route)

Brand Names:

Dosage Forms:

Uses of This Medicine:

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.

Antihistamine preparations are available both over-the-counter (OTC) and with your doctor's prescription.

Do not give any over-the-counter (OTC) cough and cold medicine to a baby or child under 4 years of age. Using these medicines in very young children might cause serious or possibly life-threatening side effects .

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 these uses are not included in product labeling, some antihistamines are used in certain patients with the following medical conditions:

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.

Before Using This Medicine:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to medicines in this group or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

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.

Do not give any over-the-counter (OTC) cough and cold medicine to a baby or child under 4 years of age. Using these medicines in very young children might cause serious or possibly life-threatening side effects .

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.

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.

Desloratadine and fexofenadine 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, and loratadine 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 cetirizine, desloratadine, or loratadine cause these same side effects.

Other medicines

Although certain medicines should not be used together at all, in other cases two 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 any of these medicines, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using medicines in this class with any of the following medicines is not recommended. Your doctor may decide not to treat you with a medication in this class or change some of the other medicines you take.

Using medicines in this class with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Other interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Using medicines in this class with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use your medicine, or give you special instructions about the use of food, alcohol, or tobacco.

Other medical problems

The presence of other medical problems may affect the use of medicines in this class. Make sure you tell your doctor if you have any other medical problems, especially:

Proper Use of This Medicine:

For patients taking this medicine by mouth:

For patients taking dimenhydrinate or diphenhydramine for motion sickness:

For patients using the suppository form of this medicine:

For patients using the injection form 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 medicines in this class 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 these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For use as an antihistamine:

For nausea, vomiting, and vertigo (only dimenhydrinate and diphenhydramine are used for vertigo):

For Parkinson's disease:

For use as a sedative (to help sleep):

For anxiety:

Missed dose

If you miss a dose of this medicine, 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.

Storage

Keep out of the reach of children.

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Do not keep outdated medicine or medicine no longer needed.

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.

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 desloratadine and loratadine. 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 . 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:

For patients using diphenhydramine or doxylamine as a sleeping aid:

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 any of the following side effects occur:

Less common or rare

Less common or rare with azatadine, cetirizine, clemastine, cyproheptadine, desloratadine, dexchlorpheniramine, diphenhydramine, or loratadine

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

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

Some 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. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
Drowsiness
dry mouth, nose, or throat
gastrointestinal upset, stomach pain, or nausea
headache
increased appetite and weight gain
thickening of mucus
Less common or rare
Acid or sour stomach
belching
blurred vision or any change in vision
body aches or pain
clumsiness or unsteadiness
confusion (not with diphenhydramine)
congestion
constipation
cough
diarrhea
difficult or painful urination
difficulty in moving
difficult or painful menstruation
dizziness (not with brompheniramine or hydroxyzine)
drowsiness (with high doses of desloratadine and loratadine)
dryness of mouth, nose, or throat
early menstruation
fast heartbeat
fever
heartburn
hoarseness
increased sensitivity of skin to sun
increased sweating
indigestion
loss of appetite
joint pain
muscle aching or cramping
muscle pains or stiffness
nausea
nightmares (not with azatadine, chlorpheniramine, cyproheptadine, desloratadine, hydroxyzine, or loratadine)
ringing or buzzing in ears
runny nose
skin rash
swollen joints
stomach discomfort, upset or pain
tender swollen glands in neck
tremor
unusual excitement, nervousness, restlessness, or irritability
vomiting

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

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.


Last Updated: 10/12/2016

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