promethazine n : antihistamine (trade name Phenergan) used to treat allergies; also an antiemetic used to treat motion sickness [syn: Phenergan]

Promethazine is a first-generation H1 receptor antagonist antihistamine and antiemetic medication. It is a prescription drug in the United States, but is available over the counter in the United Kingdom, Switzerland, and many other countries (brand names Phenergan, Promethegan, Romergan, Fargan, Farganesse, Prothiazine, Avomine, Atosil, RhinathioL).

Promethazine also has strong anticholinergic and sedative effects. Previously it was used as an antipsychotic, although it is generally not administered for this purpose now; promethazine has only approximately 1/10 of the antipsychotic strength of chlorpromazine.

Chemically, Promethazine HCl appears as a white to faint yellow crystaline powder which is practically odorless. Slow oxidation may occur upon prolonged exposure to air causing blue discoloration. Promethazine as the HCl salt is freely soluble in water and somewhat soluble in alcohol.

Indications

• As sedative
• For preoperative sedation and to counteract postnarcotic nausea
• As antiallergic medication to combat hay fever, allergic rhinitis, etc. To treat allergic reactions it can be given alone or in combination with oral decongestants like pseudo-ephedrine.
• As an adjunct treatment for anaphylactoid conditions (IM/IV route preferred).
• Together with codeine or dextromethorphan against cough
• As a motion sickness or seasickness remedy when used with Ephedrine or Pseudoephedrine.
• As an antipruritic (pruritus vulvae).
• To combat moderate to severe morning sickness and hyperemesis gravidarum. In the UK promethazine is drug of first choice being preferred as an older drug with which there is a greater experience of use in pregnancy (second line being metoclopramide or prochlorperazine). Whilst in the US, Zofran (ondansetron) is the usual drug of choice, though the high cost is prohibitive for some women.

Contraindications

• Promethazine should not be given to children under two years of age; there is potential for fatal respiratory depression in this age group.
• Hypersensitivity to phenothiazines
• Closed angle glaucoma
• Intoxication with alcohol or other central depressants
• Severe hypotension or shock
• Coma due to any reason
• Severely impaired liver function
• Urine hesitancy due to enlargement of the prostate gland

Mechanism of action

• Promethazine is a phenothiazine derivative that competitively blocks histamine H1 receptors without blocking the secretion of histamine.
• It has sedative, anti-motion-sickness, anti-emetic, and anti-cholinergic effects
• However, unlike other phenothiazines, it has no dopaminergic action due to a structural difference with other phenothiazines.

Side effects

Typical side effects are:

• Blurred vision
• Confusion in the elderly
• Drowsiness, dizziness, fatigue, more rarely vertigo
• Dry mouth
• Seizures (extremely rare)
• Neuroleptic malignant syndrome (extremely rare)
• Respiratory depression in patients under age of 2 and in those with severely compromised pulmonal function
• Constipation
• Euphoria (very rare with high IV doses and/or coadministration with opioids/CNS depressants)
• Restless legs http://www.cordingleyneurology.com/restless.htmlhttp://www.revolutionhealth.com/drugs-treatments/rating/phenergan/

Laboratory examinations

All patients should have their blood pressure measured frequently. During long-term therapy, blood cell counts, liver function studies, EKG, and EEG are recommended. The intervals should be determined according to the risk profile of the patient. In high doses Promethazine can create auditory and visual hallucinations causing panic and intense fear. If mixed with alcohol less needs to be taken to get these effects therefore can really take someone by surprise.

Recreational use

Promethazine is sometimes used as a recreational drug in conjunction with codeine in prescription cough syrup. The syrup by itself contains 7% alcohol. The traditional mixture of Sprite and cough syrup with codeine, which is known as "purple drank" or "Sizzurp", is popularized in the rap world, especially in the Houston area. It is also sometimes used to counteract nausea caused by illicit opioid use.

References

• Basic and Clinical Pharmacology

Footnotes

External links