Medications and Drugs
Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD
GENERIC NAME: promethazine
BRAND NAME: Phenergan, Phenadoz, Promethegan
DRUG CLASS AND MECHANISM: Promethazine is a phenothiazine in the same
drug class as chlorpromazine (Thorazine) and trifluoperazine (Stelazine).
However, unlike the other drugs in this class, promethazine is not used as an
anti-psychotic. It used as an anti-histamine, sedative, and
antiemetic
(anti-nausea). The body releases histamine during several types of allergic
reactions. When histamine binds to its receptors on cells, it stimulates changes
within the cells that lead to sneezing, itching, and increased mucus production.
Antihistamines such as promethazine compete with histamine for one of the
receptors for histamine (the H1 receptor) on cells. However, when the
antihistamines bind to the receptors they do not stimulate the cells. Instead,
they prevent histamine from binding and stimulating the cells. Promethazine also
blocks the action of acetylcholine (anticholinergic effect), and this may
explain its benefit in reducing the
nausea of motion sickness. It is used as a
sedative because it causes drowsiness as a side effect. The FDA approved
promethazine in 1951.
PRESCRIPTION: Yes
GENERIC AVAILABLE: Yes
PREPARATIONS: Tablets: 12.5, 25, and 50 mg; Suppositories: 12.5, 25,
and 50 mg; Syrup: 6.25 mg/5 ml; Injection: 25 and 50 mg/ml.
STORAGE: Tablets, syrup and injection should be stored at room
temperature between 15-25 C (68-77 F). Suppositories should be stored at 2-8 C
(36-46 F).
PRESCRIBED FOR: Promethazine is prescribed for treating nausea or vomiting, motion sickness, and allergic reactions and for sedation.
DOSING:
- Allergic reactions are treated with 6.25-25 mg 3 times daily.
A single 25 mg dose administered at bedtime also may suffice.
- Nausea and
vomiting may be managed with 12.5-25 mg administered every 4-6 hours as needed.
- Doses of 12.5-50 mg at bedtime are used for sedation.
- For prevention of motion
sickness, 25 mg is used 30 to 60 minutes before the motion begins and then every
8 to 12 hours as needed. Oral, rectal and injectable doses are similar.
- Promethazine injections are used when the oral route is not possible (for
example, with severe vomiting).
- Tablets may be taken with or without food.
- Suppositories are unwrapped and moistened with water before insertion into the
rectum. If the suppository is too soft from being stored in a warm place, it may
be chilled in the refrigerator for 20 to 30 minutes or placed in cold water
before the wrapper is removed.
DRUG INTERACTIONS: Promethazine should not be taken with any of the
MAO (mono-amine oxidase) inhibitor-class of antidepressants, for example,
isocarboxazid (Marplan), phenelzine (Nardil), tranylcypromine (Parnate), and
procarbazine (Matulane), because of the increased risk of extrapyramidal
symptoms (EPS)--uncontrollable movement disorders.
Excessive anti-cholinergic effects (described below) can occur when
promethazine is used with other antihistamines, for example, diphenhydramine
(Benadryl); some phenothiazines, for example,
thioridazine (Mellaril); some
tricyclic antidepressants, for example, amitriptyline (Elavil); clozapine
(Clozaril), cyclobenzaprine (Flexeril), and
disopyramide (Norpace).
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
- Drug Interactions - Learn about potential drug interactions you may be exposed to. Drug interactions can occur with prescription drugs, OTC medication, vitamins, herbs, and supplements.
- Nausea and Vomiting - Nausea and vomiting symptoms of many conditions including motion sickness, pregnancy, emotional stress, gallbladder disease, and more. Learn how to recognize the warning signs of nausea and vomiting on MedicineNet.com
- Drugs: What You Should Know About Your Drugs - Find out what you should know about your drugs such as side effects, warnings and precautions, storage information, and if a generic version is as good as the brand name.
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