Promethazine

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Promethazine

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® and Promethegan®).

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

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.
For severe Morning sickness - as an older drug with a greater experience of use during pregnancy, it is generally preferred to newer agents.

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 impared liver function
Urine hesitancy due to enlargement of the prostate gland

Side effects

Typical side effects are:

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

Dosage

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.

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.

External links

Letter from Wyeth Pharmaceuticals to practitioners regarding use of Phenergan in under twos. (PDF format)

References

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

Antiemetics | H1 receptor antagonists | Hypnotics

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