Clemastine fumarate

Manufacturing Process

9.9 g of α-methyl-p-chlorobenzhydrol are added to a suspension of 2.3 g of powdered sodamide in 30 cc of benzene. Subsequently 7.4 g of Nmethylpyrrolidyl-(2)-ethyl chloride are added and the solution is heated to the boil at reflux for 20 hours. Then shaking is first effected with water and then 4 times each time with 25 cc of 2 N hydrochloric acid. The acid extracts are made alkaline with potassium hydroxide solution while cooling strongly, and the precipitated oil is extracted with ether. After drying of the ethereal solution over potassium carbonate, the solvent is evaporated and the residue is fractionally distilled in a high vacuum, whereby N-methyl-2-[2'-(α-methyl-pchlorobenzhydryloxy)-ethyl]-pyrrolidine boils over at 154°C/0.02 mm Hg. The base is converted to the fumarate by reaction with fumaric acid.

Therapeutic Function

Antihistaminic

Biological Activity

H 1 -receptor antagonist. Clinically-used antihistamine.

Biochem/physiol Actions

Clemastine fumarate is an antihistamine H1-antagonist and anticholinergic that also has antipruritic activity.

Veterinary Drugs and Treatments

Clemastine may be used for symptomatic relief of histamine1-related allergic conditions.

Definition

ChEBI: The fumaric acid salt of clemastine. An antihistamine with antimuscarinic and moderate sedative properties, it is used for the symptomatic relief of allergic conditions such as rhinitis, urticaria, conjunctivitis and in pruritic (severe itching) skin condi ions.

Brand name

Tavist (Novartis).

General Description

Dextrorotatory clemastine, R,R-2[2[1-(4-chlorophenyl)-1-phenylethoxy]ethyl]-1- methylpyrrolidine hydrogen furnarate (1:1) (Tavist), has two chiral centers, each of which has the (R) absolute configuration. A comparison of the activities of the enantiomers indicates that the asymmetric center close to the terminal side chain nitrogen is of lesser importance to antihistaminic activity.? This member of the ethanolamine series is characterized by a long duration of action, with an activity that reaches a maximum in 5 to 7 hours and persists for 10 to 12 hours. It is well absorbed when administered orally, and it is excreted primarily in the urine. The side effects are those usually encountered with this series of antihistamines. Clemastine is closely related to chlorphenoxamine, which is used for its central cholinergic-blocking activity. Therefore, it is not surprising that clemastine has significant antimuscarinic activity.