Some commonly used brand names are:

In the U.S.—

In Canada—

Another commonly used name for trimeprazine is alimemazine.

• Antiemetic -- Promethazine
• Antihistaminic, H ₁-receptor --Methdilazine; Promethazine; Trimeprazine
• Antivertigo agent -- Promethazine
• Sedative-hypnotic --Promethazine; Trimeprazine

Phenothiazine (FEE-noe-THYE-a-zeen) -derivative 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 these antihistamines are also used to prevent motion sickness, nausea, vomiting, and dizziness. In addition, some of them may be used to help people go to sleep and control their anxiety before or after surgery.

Phenothiazine-derivative antihistamines may also be used for other conditions as determined by your doctor.

In the U.S. these antihistamines are available only with your doctor's prescription. In Canada some 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
• Methdilazine
  • Syrup (U.S.)
  • Tablets (U.S.)
  • Chewable tablets (U.S.)
• Promethazine
  • Syrup (U.S. and Canada)
  • Tablets (U.S. and Canada)
• Trimeprazine
  • Extended-release capsules (U.S.)
  • Syrup (U.S. and Canada)
  • Tablets (U.S. and Canada)

Parenteral
• Promethazine
  • Injection (U.S. and Canada)

Rectal
• Promethazine
  • Suppositories (U.S.)

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.

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

• 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

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.

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 capsule form of this medicine, swallow it whole. Do not break, crush, or chew before swallowing.

For patients taking promethazine for motion sickness :

• Take this medicine 30 minutes to 1 hour 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.

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 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 methdilazine
• For regular (short-acting) oral dosage forms (tablets or liquid):
  • For allergy symptoms:
    • Adults and teenagers—8 milligrams (mg) every six to twelve hours as needed.
    • Children younger than 3 years of age—Use and dose must be determined by your doctor.
    • Children 3 to 12 years of age—4 mg every six to twelve hours as needed.

For promethazine
• For regular (short-acting) oral dosage forms (tablets or liquid):
  • For allergy symptoms:
    • Adults and teenagers—10 to 12.5 mg four times a day before meals and at bedtime; or 25 mg at bedtime as needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 5 to 12.5 mg three times a day or 25 mg at bedtime as needed.
  • For nausea and vomiting:
    • Adults and teenagers—25 mg for the first dose, then 10 to 25 mg every four to six hours if needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 10 to 25 mg every four to six hours as needed.
  • For prevention of motion sickness:
    • Adults and teenagers—25 mg taken one-half to one hour before traveling. The dose may be repeated eight to twelve hours later if needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 10 to 25 mg one-half to one hour before traveling. The dose may be repeated eight to twelve hours later if needed.
  • For vertigo (dizziness):
    • Adults and teenagers—25 mg two times a day as needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 10 to 25 mg two times a day as needed.
  • For use as a sedative:
    • Adults and teenagers—25 to 50 mg.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 10 to 25 mg.
• For injection dosage form:
  • For allergy symptoms:
    • Adults and teenagers—25 mg injected into a muscle or into a vein.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 6.25 to 12.5 mg injected into a muscle three times a day or 25 mg at bedtime as needed.
  • For nausea and vomiting:
    • Adults and teenagers—12.5 to 25 mg injected into a muscle or into a vein every four hours as needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 12.5 to 25 mg injected into a muscle every four to six hours as needed.
  • For use as a sedative:
    • Adults and teenagers—25 to 50 mg injected into a muscle or into a vein.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 12.5 to 25 mg injected into a muscle.
• For suppository dosage form:
  • For allergy symptoms:
    • Adults and teenagers—25 mg inserted in rectum. Another 25-mg suppository may be inserted two hours later if needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 6.25 to 12.5 mg inserted into the rectum three times a day or 25 mg at bedtime as needed.
  • For nausea and vomiting:
    • Adults and teenagers—25 mg inserted into the rectum for the first dose, then 12.5 to 25 mg every four to six hours if needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 12.5 to 25 mg inserted into the rectum every four to six hours as needed.
  • For vertigo (dizziness):
    • Adults and teenagers—25 mg inserted into the rectum, two times a day as needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 12.5 to 25 mg inserted into the rectum two times a day as needed.
  • For use as a sedative:
    • Adults and teenagers—25 to 50 mg inserted into the rectum.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 years of age and older—Your doctor will determine dose based on the weight and/or size of the child. Children usually are given 12.5 to 25 mg inserted into the rectum.

For trimeprazine
• For regular (short-acting) oral dosage forms (tablets or liquid):
  • For allergy symptoms:
    • Adults and teenagers—2.5 mg four times a day as needed.
    • Children younger than 2 years of age—Use and dose must be determined by your doctor.
    • Children 2 to 3 years of age—1.25 mg at bedtime or three times a day as needed.
    • Children 3 to 12 years of age—2.5 mg at bedtime or three times a day as needed.
• For long-acting oral dosage forms (extended-release capsules):
  • For allergy symptoms:
    • Adults and teenagers—5 mg every twelve 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—5 mg once a day as needed.

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.

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.

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

When taking phenothiazine-derivative 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.

Phenothiazine-derivative 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. Make sure you know how you react to the phenothiazine-derivative antihistamine you are taking before you drive, use machines, or do anything else that could be dangerous if you are not alert.

Phenothiazine-derivative antihistamines may cause dryness of the mouth, nose, and throat. 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.

This medicine controls nausea and vomiting. For this reason, it may cover up some of 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.

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 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);  muscle spasms (especially of neck and back) ;  restlessness;  shortness of breath or troubled breathing;  shuffling walk;  tic-like (jerky) movements of head and face;  trembling and shaking of hands;  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 (less common with methdilazine);  thickening of mucus 
  
  

• Less common or rare
  • Blurred vision or any change in vision;  burning or stinging of rectum (with rectal suppository);  confusion;  difficult or painful urination;  dizziness;  dryness of mouth, nose, or throat;  fast heartbeat;  feeling faint;  increased sensitivity of skin to sun ;  increased sweating;  loss of appetite;  nightmares;  ringing or buzzing in ears;  skin rash;  unusual excitement, nervousness, restlessness, or irritability  
  
  

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