ANTIHIST 2% W/W CREAM

Indications

• Allergic rhinitis
• Urticaria
• Pruritus
• Allergic conjunctivitis
• Anaphylactic reactions (adjunctive treatment)

Dosage

Children: Refer to the BNF for Children for appropriate pediatric dosing guidelines.

Adults: Refer to the BNF for specific dosing recommendations based on the condition being treated, as dosing may vary.

Mechanism of action

Mepyramine binds to the histamine H1 receptor, promoting a G protein-coupled inactive state that interferes with Gq/11-mediated signaling. By competing with histamine for binding at H1-receptor sites, it suppresses histaminic responses, including edema, flare, and itching. Its sedative properties are linked to actions within the central nervous system, while its anticholinergic effects provide a drying action on the nasal mucosa.

Pharmacodynamics

As an H1 receptor antagonist, mepyramine inhibits the effects of histamine, which include increased vascular permeability, smooth muscle contraction, and sensory nerve stimulation. This leads to reduced symptoms of allergic responses, such as swelling and itchiness. Mepyramine also demonstrates anticholinergic properties, resulting in additional drying effects on mucosal surfaces.

Pharmacokinetics

Mepyramine is absorbed through the gastrointestinal tract and distributed throughout the body. It crosses the blood-brain barrier, which contributes to its sedative effects. The drug is metabolized in the liver and excreted primarily via urine. The onset of action can vary but is generally within 1 to 2 hours, with a duration of effect that can last several hours.

Adverse effects

• Drowsiness
• Dry mouth
• Dizziness
• Blurred vision
• Gastrointestinal disturbances

Interactions

• CNS depressants may enhance sedative effects
• Alcohol may increase the risk of sedation and dizziness

Precautions

• Use with caution in patients with glaucoma
• Use with caution in patients with urinary retention
• Caution in patients with respiratory conditions such as asthma

Pregnancy

Mepyramine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Mepyramine is excreted in breast milk; caution should be exercised when administered to nursing mothers.

Storage

Store in a cool, dry place away from direct sunlight.

Formulations

• Tablets
• Syrup

Mechanism of action

Mepyramine is a histamine H1 receptor inverse agonist. It binds to a G protein-coupled form of the receptor and promotes a G protein-coupled inactive state of the H1 receptor that interferes with the Gq/11-mediated signaling. Mepyramine competes with histamine for binding at H₁-receptor sites on the effector cell surface, resulting in suppression of histaminic edema, flare, and pruritus. The sedative properties of Mepyramine occur at the subcortical level of the CNS. 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/ 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/ H1 antagonists strongly block the action of histamine that results in increased permeability and formation of edema and wheal. /Histamine Antagonists: H1 Antagonists/ Some H1 antagonists possess local anesthetic activity ... . /Histamine Antagonists: H1 Antagonists/ For more Mechanism of Action (Complete) data for PYRILAMINE (6 total), please visit the HSDB record page.