ALLEREX SYRUP

Indications

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

Dosage

Children: Refer to BNF for Children for specific dosing information.

Adults: Refer to BNF for specific dosing information.

Mechanism of action

Chorpheniramine exerts its effects by antagonizing the H1 histamine receptors, which prevents histamine from binding and activating these receptors. This action reduces the physiological effects of histamine, including vasodilation and increased vascular permeability, leading to a decrease in allergy symptoms. Additionally, chorpheniramine has some anticholinergic effects, which can contribute to its efficacy in relieving allergic symptoms.

Pharmacodynamics

As an antihistamine, chorpheniramine competes with histamine for binding to H1 receptors, leading to a reduction in the pharmacological effects associated with histamine release. The onset of action typically occurs within 1-2 hours after oral administration and can last for 4-6 hours, although the duration may vary between individuals.

Pharmacokinetics

Chorpheniramine is well absorbed from the gastrointestinal tract. It undergoes hepatic metabolism and is primarily excreted in the urine. The half-life of chorpheniramine is approximately 12-13 hours, but this can be prolonged in elderly patients or those with liver impairment. Food does not significantly affect the absorption of chorpheniramine.

Contra-indications

• Hypersensitivity to chorpheniramine or any of its components
• Severe asthma or bronchial obstruction
• Use in neonates and premature infants
• Concurrent use of monoamine oxidase inhibitors (MAOIs)

Adverse effects

• Drowsiness
• Dizziness
• Dry mouth
• Constipation
• Blurred vision
• Urinary retention
• Gastrointestinal disturbances

Interactions

• Increased sedation when used with alcohol, sedatives, or tranquilizers
• Potentially increased anticholinergic effects when combined with other anticholinergic medications
• Increased risk of hypertensive crisis when used with MAOIs

Precautions

• Use with caution in patients with glaucoma
• Use with caution in patients with prostatic hypertrophy
• May exacerbate asthma or other respiratory conditions
• Caution in patients with cardiovascular disease due to potential anticholinergic effects

Pregnancy

Chorpheniramine is classified as Category B. Animal reproduction studies have not shown a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women.

Breast-feeding

Chorpheniramine is excreted in breast milk. Caution is advised when administered to nursing mothers.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Tablets
• Extended-release tablets
• Syrup
• Injection