Clemastine Fumarate Dailymed

Rx only

Description

Clemastine belongs to the benzhydryl ether group of antihistaminic compounds. The chemical name is (+)-(2R)-2-[2-[[(R)-p-Chloro-α-methyl-α-phenylbenzyl]-oxy]ethyl]-1-methylpyrrolidine fumarate (1:1).

C₂₁H₂₆C1NO.C₄H₄O₄ M.W. 459.97 Each tablet for oral administration contains 2.68 mg of clemastine fumarate, USP.

Inactive ingredients: colloidal silicon dioxide, corn starch, lactose monohydrate, povidone, pregelatinized starch and stearic acid.

Clinical Pharmacology

Clemastine fumarate is an antihistamine with anticholinergic (drying) and sedative side effects. Antihistamines appear to compete with histamine for cell receptor sites on effector cells. The inherently long duration of antihistaminic effects of clemastine fumarate has been demonstrated in wheal and flare studies. In normal human subjects who received histamine injections over a 24-hour period, the antihistaminic activity of clemastine reached a peak at 5 to 7 hours, persisted for 10 to 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 and nearly completely absorbed from the gastrointestinal tract, peak plasma concentrations are attained in 2 to 4 hours, and urinary excretion is the major mode of elimination.

Indications And Usage

Clemastine Fumarate Tablets USP, 2.68 mg are indicated for the relief of symptoms associated with allergic rhinitis such as sneezing, rhinorrhea, pruritus, and lacrimation. Clemastine Fumarate Tablets USP, 2.68 mg are also indicated for the relief of mild, uncomplicated allergic skin manifestations of urticaria and angioedema. It should be noted that clemastine fumarate is indicated for the dermatologic indications at the 2.68 mg dosage level only.

Contraindications

Usage in Nursing Mothers

Because of the higher risk of antihistamines for infants generally and for newborns and prematures in particular, antihistamine therapy is contraindicated in nursing mothers.

Usage in Lower Respiratory Disease

Antihistamines should not be used to treat lower respiratory tract symptoms including asthma. Antihistamines are also contraindicated in the following conditions:

Hypersensitivity to clemastine fumarate or other antihistamines of similar chemical structure.

Monoamine oxidase inhibitor therapy (see Drug Interactions section).

Warnings

Antihistamines should be used with considerable caution in patients with: narrow angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, symptomatic prostatic hypertrophy, and bladder neck obstruction.

Usage in Children

Safety and efficacy of clemastine fumarate have not been established in children under the age of 12 years.

Usage in Pregnancy

Experience with this drug in pregnant women is inadequate to determine whether there is exists a potential for harm to the developing fetus.

Usage with CNS Depressants

Clemastine has additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc.).

Usage in Activities Requiring Mental Alertness

Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc.

Usage in the Elderly (approximately 60 years or older)

Antihistamines are more likely to cause dizziness, sedation, and hypotension in elderly patients.

Clemastine fumarate should be used with caution in patients with: history or bronchial asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease, and hypotension.

Drug Interactions

MAO inhibitors prolong and intensify the anticholinergic (drying) effects of antihistamines.

Adverse Reactions

Transient drowsiness, the most common adverse reaction associated with clemastine fumarate, occurs relatively frequently and may require discontinuation of therapy in some instances. \

Antihistaminic Compounds

It should be noted that the following reactions have occurred with one or more antihistamines and, therefore, should be kept in mind when prescribing drugs belonging to this class, including clemastine. The most frequent adverse reactions are italicized.

• General: Urticaria, drug rash, anaphylactic shock, photosensitivity, excessive perspiration, chills, dryness of the mouth, nose, and throat.
• Cardiovascular System: Hypotension, headache, palpitations, tachycardia, extrasystoles.
• Hematologic System: Hemolytic anemia, thrombocytopenia, agranulocytosis.
• Nervous System: Sedation, sleepiness, dizziness, disturbed coordination, fatigue, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesias, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, hysteria, neuritis, convulsions.
• GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation.
• GU System: Urinary frequency, difficult urination, urinary retention, early menses.
• Respiratory System: Thickening of bronchial secretions, tightness of chest and wheezing, nasal stuffiness.