Antihistamines, Phenothiazine-derivative (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 phenothiazine-derivative antihistamines, the following should be considered:

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

Pregnancy - Methdilazine, promethazine, and trimeprazine have not been studied in pregnant women. In animal studies, promethazine has not been shown to cause birth defects. However, other phenothiazine medicines caused jaundice and muscle tremors in a few newborn babies whose mothers received these medicines during pregnancy. Also, the newborn baby may have blood clotting problems if promethazine is taken by the mother within 2 weeks before delivery.

Breast-feeding - Small amounts of antihistamines pass into the breast milk. Use by nursing mothers is not recommended since babies are more sensitive to the side effects of antihistamines, such as unusual excitement or irritability. Also, with the use of phenothiazine-derivative antihistamines there is the chance that the nursing baby may be more at risk of having difficulty in breathing while sleeping or of the sudden infant death syndrome (SIDS). However, more studies are needed to confirm this.

In addition, 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.

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. The use of phenothiazine-derivative antihistamines is not recommended in children who have a history of difficulty in breathing while sleeping, or a family history of sudden infant death syndrome (SIDS) .

Children who show signs of Reye's syndrome should not be given phenothiazine-derivative antihistamines, especially by injection. Uncontrolled movements that may occur with phenothiazine-derivative antihistamines may be mistakenly confused with symptoms of Reye's syndrome.

Adolescents - Adolescents who show signs of Reye's syndrome should not be given phenothiazine-derivative antihistamines, especially by injection. Uncontrolled movements that may occur with phenothiazine-derivative antihistamines may be mistakenly confused with symptoms of Reye's syndrome.

Older adults - Elderly patients are especially sensitive to the effects of antihistamines. Confusion; difficult or painful urination; dizziness; drowsiness; feeling faint; or dryness of the 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. In addition, uncontrolled movements may be more likely to occur in elderly patients taking phenothiazine-derivative antihistamines.

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 taking phenothiazine-derivative antihistamines, it is especially important that your health care professional know if you are taking/receiving any of the following:

• Amoxapine (e.g., Asendin) or
• Antipsychotics (medicine for mental illness) or
• Methyldopa (e.g., Aldomet) or
• Metoclopramide (e.g., Reglan) or
• Metyrosine (e.g., Demser) or
• Pemoline (e.g., Cylert) or
• Pimozide (e.g., Orap) or
• Rauwolfia alkaloids (alseroxylon [e.g., Rauwiloid], deserpidine [e.g., Harmonyl], rauwolfia serpentina [e.g., Raudixin], reserpine [e.g., Serpasil]) - Side effects of these medicines, such as uncontrolled body movements, may become more severe and frequent if they are used together with phenothiazine-derivative antihistamines

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

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

• Contrast agent, injected into spinal canal - If you are having an x-ray test of the head, spinal canal, or nervous system for which you are going to receive an injection into the spinal canal, phenothiazine-derivative antihistamines may increase the chance of seizures; stop taking any phenothiazine-derivative antihistamine 48 hours before the test and do not start taking it until 24 hours after the test

• Levodopa - When used together with phenothiazine-derivative antihistamines, the levodopa may not work as it should

• Monoamine oxidase (MAO) inhibitor activity (isocarboxazid [e.g., Marplan], isocarboxazid [e.g., Marplan], phenelzine [e.g., Nardil], procarbazine [e.g., Matulane], selgiline [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 phenothiazine-derivative 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:

• Blood disease or
• Heart or blood vessel disease - These medicines may cause more serious conditions to develop

• Enlarged prostate or
• Urinary tract blockage or difficult urination - Phenothiazine-derivative antihistamines may cause urinary problems to become worse

• Epilepsy - Phenothiazine-derivative antihistamines, especially promethazine given by injection, may increase the chance of seizures

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

• Jaundice - Phenothiazine-derivative antihistamines may make the condition worse

• Liver disease - Phenothiazine-derivative antihistamines may build up in the body, which may increase the chance of side effects such as muscle spasms

• Reye's syndrome - Phenothiazine-derivative antihistamines, especially promethazine given by injection, may increase the chance of uncontrolled movements