Clemastine Fumarate Syrup (Clemastine Fumarate Syrup) Drug Information: Clinical Pharmacology

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May 26, 2012

Clemastine Fumarate Syrup

Hay Fever »

What is hay fever? What are the symptoms and signs?

Hay fever is a misnomer. Hay is not a usual cause of this problem, and it does not cause fever. Early descriptions of sneezing, nasal congestion, and eye irritation while harvesting field hay promoted this popular term. Allergic rhinitis is the correct term used to describe this allergic reaction, and many different substances cause the allergic symptoms noted in hay fever. Rhinitis means "irritation of the nose" and is a derivative of rhino, meaning nose. Allergic rhinitis which occurs during a specific season is called "seasonal allergic rhinitis." When it occurs throughout the year, it is called "perennial allergic rhinitis." Rhinosinusitis is the medical term that refers to inflammation of the nasal lining as well as the lining tissues of the sinuses. This term is sometime used because the two conditions frequently occur together.

Symptoms of allergic rhinitis, or hay fever...

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Clemastine Fumarate Syrup

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CLINICAL PHARMACOLOGY

Clemastine fumarate is an antihistamine with anticholinergic (drying) and sedative side effects. Antihistamines competitively antagonize various physiological effects of histamine including increased capillary permeability and dilatation, the formation of edema, the "flare" and "itch" response, and gastrointestinal and respiratory smooth muscle constriction. Within the vascular tree, H₁-receptor antagonists inhibit both the vasoconstrictor and vasodilator effects of histamine. Depending on the dose, H₁-receptor antagonists can produce CNS stimulation or depression. Most antihistamines exhibit central and/or peripheral anticholinergic activity. Antihistamines act by competitively blocking H₁-receptor sites. Antihistamines do not pharmacologically antagonize or chemically inactivate histamine, nor do they prevent the release of histamine.

Pharmacokinetics

Antihistamines are well-absorbed following oral administration. Chlorpheniramine maleate, clemastine fumarate, and diphenhydramine hydrochloride achieve peak blood levels within 2-5 hours following oral administration. The absorption of antihistamines is often partially delayed by the use of controlled release dosage forms. In these instances, plasma concentrations from identical doses of the immediate and controlled release dosage forms will not be similar. Tissue distribution of the antihistamines in humans has not been established. Antihistamines appear to be metabolized in the liver chiefly via mono- and didemethylation and glucuronide conjugation. Antihistamine metabolites and small amounts of unchanged drug are excreted in the urine. Small amounts of the drugs may also be excreted in breast milk.

In normal human subjects who received histamine injections over a 24-hour period, the antihistaminic activity of clemastine reached a peak at 5-7 hours, persisted for 10-12 hours and, in some cases, for as long as 24 hours. Pharmacokinetic studies in man utilizing ³H and ¹⁴C labeled compound demonstrates that: clemastine is rapidly absorbed from the gastrointestinal tract, peak plasma concentrations are attained in 2-4 hours, and urinary excretion is the major mode of elimination.

Last reviewed on RxList: 8/11/2008
This monograph has been modified to include the generic and brand name in many instances.