Dexchlorpheniramine

Dexchlorpheniramine under the trade name Polaramine is an antihistamine drug with anticholinergic properties that is used to treat allergic conditions such as hay fever or urticaria. Polaramine (dexchlorpheniramine maleate) is available as a tablet for immediate release oral use and as a syrup.

Mechanism of action:
Dexchlorpheniramine competes with histamine for binding at the H1-receptor sites and competitively antagonizes the effects of histamine on the H1 receptors. It does not prevent the release of histamine. Blocking the H1-receptors suppresses the formation of the oedema, flare, and pruritus that results from increased histamine activity. Dexchlorpheniramine can bind to both central and peripheral H1-receptors, so does have some sedative effects.

Pharmocokinetics:
Well absorbed from the GI tract with onset of action in about 30-60 minutes; the maximum therapeutic effect can take about 6 hours and the duration of action lasts between 4-8 hours.
Protein binding is about 70%
The half-life in healthy adults is 20-24 hours.

Contraindications: children under 2 years of age (respiratory suppression risks); those taking monoamine oxidase inhibitors (MAOIs); previous history of hypersensitivity to dexchlorpheniramine.

Caution in those narrow-angle glaucoma; peptic ulcer; bladder neck obstruction; pyloroduodenal obstruction; hypertension; increased intraocular pressure; hyperthyroidism; renal or hepatic impairment. Safety during pregnancy has not been established. Dexchlorpheniramine is excreted in breast milk.

Side effects: drowsiness is the most common

Chemical formula: C₁₆H₁₉ClN₂.C₄H₄O₄

In Australia, this is an S3, pharmacy only medication. The Polaramine brand has been discontinued in the USA.

Other H1 Antagoinsts/Antihistamines:

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