Promethazine Totally Explained

Everything about Promethazine totally explained

, | PubChem = 4927 | DrugBank = APRD00601 | C = 17 |H = 20 |N = 2 |S = 1 | molecular_weight = 284.425 g/mol | bioavailability = 88% absorbed but after first-pass metabolism reduced to 25% absolute bioavailability | protein_bound = 93% | metabolism = Hepatic glucuronidation and sulfoxidation | elimination_half-life = 16-19 hours | excretion = Renal and biliary | pregnancy_AU = C | pregnancy_US = C | pregnancy_category = | legal_AU = | legal_UK = P | legal_US = Rx-only | 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, Farganesse, Prothiazine, Avomine, Atosil, RhinathioL).
Promethazine also has strong anticholinergic and sedative effects. Previously it was used as an antipsychotic, although it's generally not administered for this purpose now; promethazine has only approximately 1/10 of the antipsychotic strength of chlorpromazine.

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's 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 shouldn't be given to children under two years of age; there's 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 (External Link

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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 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.

Further Information

Get more info on 'Promethazine'.

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