Clemastine is a first-generation antihistamine medication used primarily for the treatment of allergic conditions such as allergic rhinitis (hay fever), allergic conjunctivitis, and itching associated with chronic urticaria (hives). It provides rapid relief of symptoms but requires twice-daily dosing and may cause sedation and other CNS side effects. Brand names: Tavist Allergy, Dayhist Allergy.
Key points:
-
Action: Clemastine blocks the effects of histamine at H1 receptors, thereby alleviating symptoms such as sneezing, itching, runny nose, and watery eyes caused by allergic reactions.
-
Indications: For the relief of symptoms associated with allergic rhinitis (both seasonal and perennial), allergic conjunctivitis, and chronic idiopathic urticaria (hives).
-
Administration: The usual dosage of clemastine for adults and children aged 12 years and older is 1 tablet (1.34 mg) taken orally every 12 hours, with a maximum daily dose of 6 tablets (8.04 mg). Clemastine is typically taken with water, with or without food.
-
Timing: Clemastine has a relatively rapid onset of action, with symptom relief typically occurring within 1 hour after administration. The duration of action is generally 4 to 6 hours per dose, requiring twice-daily dosing.
-
Safety: Like other first-generation antihistamines, it has a higher incidence of sedation and central nervous system (CNS) side effects compared to second-generation antihistamines. Common side effects may include drowsiness, dizziness, dry mouth, blurred vision, constipation, and urinary retention.
-
Contraindications: It should not be used in patients with narrow-angle glaucoma, urinary retention, severe liver disease, or severe respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD). Use with caution in elderly patients, as they may be more susceptible to CNS side effects.