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Promethazine chemical structure
| N, N-dimethyl-1-(10H-phenothiazin-10-yl)propan-2-amine|
| CAS number |
| ATC code |
| PubChem |
| DrugBank |
|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|
|Legal status|| |
|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.
- 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.
- 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
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
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
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.
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]
- Letter from Wyeth Pharmaceuticals to practitioners regarding use of Phenergan in under twos. (PDF format)
- Basic and Clinical Pharmacology, 9th ed (2004). Katzung, Bertram G. pp. 264–265.
(Acrivastine) (Astemizole) (Azelastine) (Brompheniramine) (Carbinoxamine) (Cetirizine) (Chlorphenamine) (Clemastine) (Desloratadine) (Dimenhydrinate) (Diphenhydramine) (Doxylamine) (Loratadine) (Fexofenadine) (Meclizine) (Promethazine) (Triprolidine)
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