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Promethazine chemical structure
Promethazine

N, N-dimethyl-1-(10H-phenothiazin-10-yl)propan-2-amine
IUPAC name
CAS number
60-87-7
ATC code

D04AA10 ., .

PubChem
4927
DrugBank
APRD00601
Chemical formula {{{chemical_formula}}}
Molecular weight 284.425 g/mol
Bioavailability 88% absorbed but after first-pass metabolism reduced to 25% absolute bioavailability
Metabolism Hepatic glucuronidation and sulfoxidation
Elimination half-life 16-19 hours
Excretion Renal and biliary
Pregnancy category
Legal status
(injection POM(UK))
Routes of administration Oral, rectal, IV, IM

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®).

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.

Indications[edit | edit source]

  • As sedative/hypnotic
  • 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.
  • Together with codeine or dextromethorphan against cough
  • It can be used to increase the activity of opioids. It allows lower opioid doses and decreases their emetic properties.
  • As a motion sickness or seasickness when used with Ephedrine or Pseudoephedrine.
  • As an antipruritic (pruritus vulvae).
  • To combat moderate to severe morning sickness and hyperemesis gravidarum.

Contraindications[edit | edit source]

  • 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

Side effects[edit | edit source]

Typical side effects are:

  • Blurred vision
  • Confusion in the elderly
  • Drowsiness, dizziness, fatigue, more rarely vertigo
  • Dry mouth
  • Seizures (extremely rare)
  • Malignant neuroleptic syndrome (extremely rare)
  • Respiratory depression in patients under age of 2 and in those with severely compromised pulmonal function
  • Constipation

Dosage[edit | edit source]

Depending on disease and clinical condition (age, liver function):

  • Mild to moderate cases of agitation: 25–50 mg orally, 3 to 4 times daily
  • Insomnia: depending upon severity, 25–100 mg orally at bedtime

In pediatric patients doses as low as 5–10 mg, 3 times daily may suffice. For precise dosing syrup forms exist.

As an anti-emetic:

  • Adult: 6.25 mg IV, or 12.5 mg IM
  • Pediatric (greater than 2 years old): 0.25 mg/kg IV/ IM

Laboratory examinations[edit | edit source]

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.

Recreational use[edit | edit source]

Promethazine is sometimes used as a recreational drug in conjunction with Codeine in prescription cough syrup. The mixture of Sprite and cough syrup with codeine is popularized in the rap world, especially in the Houston area.[How to reference and link to summary or text]

External links[edit | edit source]

References[edit | edit source]

  • Basic and Clinical Pharmacology, 9th ed (2004). Katzung, Bertram G. pp. 264–265.


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