Promethazine

Promethazine is a prescription drug used for the treatment of various allergy symptoms and motion sickness as well as to induce sedation and prevent vomiting. It belongs to a family of anti-allergy drugs called H1-receptor antagonists. Other members of this family include alimemazine (trimeprazine) and cyproheptadine. Promethazine is marketed as Phenergan by Wyeth and was approved in 1951.

Uses

Promethazine is indicated for:

• Allergic rhinitis
• Vasomotor rhinitis
• Allergic conjunctivitis
• Mild, uncomplicated allergic skin manifestations of urticaria and angioedema
• Treatment of allergic reactions to blood or plasma
• Dermographism
• Anaphylaxis
• Preoperative, postoperative, or obstetric sedation
• Prevention and control of nausea and vomiting associated with certain types of anesthesia and surgery
• Therapy adjunctive to meperidine or other analgesics for control of post-operative pain
• Sedation to aid sleep
• Motion sickness
• Antiemetic therapy in postoperative patients

Promethazine is occasionally used a recreational drug in combination with cough syrup, notably in and around Houston.^[1] Promethazine is also sometimes used with opioids to counteract the nausea they cause.

How Promethazine is Taken

Promethazine can be taken as oral tablets, by injection, or as a rectal suppository. Tablet strengths include 12.5 mg, 25 mg, and 50 mg.

For Allergies

The average oral dose is 25 mg taken before bedtime; however, 12.5 mg may be taken before meals and at bedtime, if necessary.

For Motion Sickness

The average adult dose is 25 mg taken twice daily. The initial dose should be taken one-half to one hour before anticipated travel and be repeated 8 to 12 hours later, if necessary. For children, Phenergan, 12.5 to 25 mg, twice daily, may be administered.

For Nausea and Vomiting

The average effective dose of promethazine for the active therapy of nausea and vomiting in children or adults is 25 mg.

For nausea and vomiting in children, the usual dose is 0.5 mg per pound of body weight, and the dose is adjusted to the age and weight of the patient and the severity of the condition being treated.

For prophylaxis of nausea and vomiting, as during surgery and the postoperative period, the average dose is 25 mg repeated at 4- to 6-hour intervals, as necessary.

For Sedation

Administration of 12.5 to 25 mg promethazine by the oral route or by rectal suppository at bedtime will provide sedation in children. Adults usually require 25 to 50 mg for nighttime, presurgical, or obstetrical sedation.

For Pre- and Postoperative Use

Promethazine in 12.5- to 25-mg doses for children and 50-mg doses for adults the night before surgery relieves apprehension and produces a quiet sleep.

For preoperative medication, children require doses of 0.5 mg per pound of body weight in combination with an appropriately reduced dose of narcotic or barbiturate and the appropriate dose of an atropine-like drug. Usual adult dosage is 50 mg promethazine with an appropriately reduced dose of narcotic or barbiturate and the required amount of a belladonna alkaloid.

Postoperative sedation and adjunctive use with analgesics may be obtained by the administration of 12.5 to 25 mg in children and 25- to 50-mg doses in adults.

How Promethazine Works

Like many other anti-allergy medications, promethazine works by blocking the histamine H1 receptor. Histamine release by mast cells is responsible for many symptoms of allergic reactions. Promethazine essentially prevents this released histamine from acting by blocking the histamine H1 receptor.^[2]

How the Body Affects Promethazine

Promethazine is well absorbed from the gastrointestinal tract. Effects are usually noticed within 20 minutes after dosing and generally last 4-6 hours.

Promethazine is metabolized by the liver into a variety of metabolites. These are eliminated via the urine.

Side Effects

Drowsiness is by far the most prominent side effect of using promethazine.

Risks and Precautions

Promethazine may cause drowsiness and impair the ability to perform potentially hazardous tasks, such as driving a vehicle or operating heavy machinery. Prolonged exposure to the sun should be avoided while on promethazine.

It is well-known that promethazine must not be injected into the arteries. In a product-liability lawsuit that was recently heard by the US Supreme Court (Wyeth v. Levine), the plaintiff (Diana Levine) was given promethazine by injection and her arterial blood was inadvertently exposed. She subsequently experienced gangrene and eventual amputation of her hand and forearm, illustrating the need for caution when injecting this drug.^[3]

Drug Interactions

• Promethazine may intensify the sedative action of other depressants, such as alcohol, sedatives/hypnotics, narcotics, anesthetics, tricyclic antidepressants, and tranquilizers; therefore, such agents need to be avoided or administered in reduced dosage in patients receiving promethazine.

• Because of the potential for promethazine to reverse epinephrine's effect on increasing blood pressure, epinephrine should NOT be used to treat low blood pressure associated with promethazine.

• Concurrent use of other agents with anticholinergic properties should be undertaken with caution.

• Drug interactions have been reported when some MAOI and phenothiazines are used concurrently.

Effectiveness

At this point in time, there are no well-designed studies available attesting to the effectiveness of promethazine over other medications for allergies, sedation and vomiting.

References

1. ↑ Peters RJ Jr, Kelder SH, Markham CM, Yacoubian GS Jr, Peters LA, Ellis A. Beliefs and social norms about codeine and promethazine hydrochloride cough syrup (CPHCS) onset and perceived addiction among urban Houstonian adolescents: an addiction trend in the city of lean. J Drug Educ. 2003;33(4):415-25. Abstract
2. ↑ BURN JH. The pharmacology of chlorpromazine and promethazine. Proc R Soc Med. 1954 Aug;47(8):617-21. Citation
3. ↑ Walker EP, High Court Hears Oral Arguments on FDA Labels v. State Tort Statutes. MedPage Today, November 3, 2008. Accessed November 29, 2008.

External Links

• MedlinePlus
• FDA: Patient Information Sheet
• Drugs.com
• Rx List