Clemastine

Introduction

Clemastine fumarate is a white crystalline powder, very slightly soluble in water slightly soluble in alcohol, and methanol. It has two chiral centers, each of which is (R) absolute configuration. A comparison of the activities of the antipodes indicates that the asymmetric center close to the side chain of nitrogen is of lesser importance to antihistaminic activity. It is a long-acting ethanolamine antihistamine with sedative and anticholinergic side effects.

Structure

Synthesis

Mechanism of Action:

Clemastine selectively antagonizes the histamine H1 receptor, inhibiting the action of endogenous histamine. This inhibition results in temporary relief from the negative symptoms induced by histamine.

Properties and uses:

• Commonly used to treat symptoms of allergic conditions, including allergic rhinitis (hay fever), hives (urticaria), and itching.
• It may be found in over-the-counter allergy medications and cough and cold preparations.

Assay: 

Dissolve the sample in anhydrous acetic acid and titrate against 0.1 M perchloric acid. Determine the end-point potentiometrically.

Dosage forms: 

Clemastine oral solution B.P., Clemastine tablets B.P.