Antihistamines (Systemic)

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.

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.

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

• Erythromycin (e.g., E-Mycin) or
• Ketoconazole (e.g., Nizoral) - Use of these medicines with fexofenadine may cause an increased amount of fexofenadine in the blood.

• 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

• Monoamine oxidase (MAO) inhibitor activity (isocarboxazid [e.g., Marplan], 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

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

• Intestinal obstruction or
• Stomach ulcer - Use of cyproheptadine may make these conditions worse.

• Liver disease or
• Kidney disease - Effects of desloratadine may be increased because of slower removal from the body.