HISTADEX

Indications

• Allergic rhinitis
• Urticaria
• Allergic conjunctivitis
• Common cold symptoms

Dosage

Children: For children aged 6 to 12 years, the recommended dose is 1 to 2 mg every 4 to 6 hours, not exceeding 6 mg per day. For children aged 2 to 6 years, refer to the BNF for Children for specific dosing recommendations.

Adults: The typical adult dose for allergic conditions is 2 to 4 mg taken every 4 to 6 hours, not exceeding 24 mg per day.

Mechanism of action

Dexchlorpheniramine antagonizes histamine H1 receptors, competing with histamine for binding sites on effector cells. This prevents the actions mediated by histamine, such as urticaria and pruritus. Additionally, its anticholinergic effects lead to a drying effect on nasal mucosa, further alleviating allergy symptoms.

Pharmacodynamics

As an H1 receptor antagonist, dexchlorpheniramine reduces the physiological effects of histamine, including vascular permeability, smooth muscle contraction, and stimulation of sensory nerves. Its anticholinergic properties can cause sedation and dry secretions, which are common side effects associated with first-generation antihistamines.

Pharmacokinetics

Dexchlorpheniramine is well absorbed from the gastrointestinal tract. It has a moderate volume of distribution and is metabolized in the liver. The drug has a relatively long half-life, allowing for once or twice daily dosing in most cases. The elimination of the drug occurs primarily through urinary excretion of its metabolites.

Contra-indications

• Hypersensitivity to dexchlorpheniramine or any of its components
• Severe asthma
• Narrow-angle glaucoma
• Prostatic hypertrophy

Adverse effects

• Drowsiness
• Dry mouth
• Dizziness
• Nausea
• Constipation
• Blurred vision

Interactions

• Increased sedation when used with alcohol, opioids, or other central nervous system depressants
• May enhance the anticholinergic effects of other medications with anticholinergic properties

Precautions

• Use with caution in patients with hepatic impairment
• Caution in patients with a history of seizures
• Should be used with caution in elderly patients due to increased sensitivity

Pregnancy

Dexchlorpheniramine is classified as category B. Animal studies have not shown any risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. Use only if clearly needed.

Breast-feeding

Dexchlorpheniramine is excreted in breast milk, and caution should be exercised when administering to nursing mothers.

Storage

Store below 25°C. Protect from light and moisture.

Formulations

• Tablets
• Syrup

Mechanism of action

Dexchlorpheniramine is an antihistamine that antagonizes histamine H1 receptors. Antihistamines used in the treatment of allergy act by competing with histamine for H1-receptor sites on effector cells. They thereby prevent, but do not reverse, responses mediated by histamine alone. Antihistamines antagonize, in varying degrees, most of the pharmacological effects of histamine, including urticaria and pruritus. Also, the anticholinergic actions of most antihistamines provide a drying effect on the nasal mucosa. /Antihistamines/ DEXCHLORPHENIRAMINE MALEATE ANTAGONIZES MANY OF CHARACTERISTIC EFFECTS OF HISTAMINE. WHEN TESTED IN DOGS, ANTIHISTAMINIC POTENCY OF DEXTRO ISOMER WAS 100 TIMES GREATER THAN THAT OF LEVO ISOMER, & 2.5 TIMES GREATER THAN RACEMIC FORM. ON CIRCUS-MOVEMENT ATRIAL FLUTTER, LEVO FORM WAS 1.4 & 2.3 TIMES THAT OF RACEMIC & DEXTRO CMPD. H1 antagonists inhibit most responses of smooth muscle to histamine. Antagonism of the constrictor action of histamine on respiratory smooth muscle is easily shown in vivo and in vitro. /Histamine Antagonists: H1 Antagonists/ For more Mechanism of Action (Complete) data for DEXCHLORPHENIRAMINE (7 total), please visit the HSDB record page.