| Item |
Information |
|
Drug Groups
|
approved |
|
Description
|
An ethanolamine-derivative, first generation histamine H1 antagonist used in hay fever, rhinitis, allergic skin conditions, and pruritus. It causes drowsiness. [PubChem] |
| Indication |
For the relief of symptoms associated with allergic rhinitis such as sneezing, rhinorrhea, pruritus and acrimation. Also for the management of mild, uncomplicated allergic skin manifestations of urticaria and angioedema. Used as self-medication for temporary relief of symptoms associated with the common cold. |
| Pharmacology |
Clemastine 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. |
| Toxicity |
Oral LD50 in rat and mouse is 3550 mg/kg and 730 mg/kg, respectively. Antihistamine overdosage reactions may vary from central nervous system depression to stimulation. In children, stimulation predominates initially in a syndrome which may include excitement, hallucinations, ataxia, incoordination, muscle twitching, athetosis, hyperthermia, cyanosis convulsions, tremors, and hyperreflexia followed by postictal depression and cardio-respiratory arrest. Convulsions in children may be preceded by mild depression. Dry mouth, fixed dilated pupils, flushing of the face, and fever are common. In adults, CNS depression, ranging from drowsiness to coma, is more common. |
| Affected Organisms |
| • |
Humans and other mammals |
|
| Biotransformation |
Antihistamines appear to be metabolized in the liver chiefly via mono- and didemethylation and glucuronide conjugation. |
| Absorption |
Rapidly absorbed from the gastrointestinal tract. |
| Elimination |
Urinary excretion is the major mode of elimination. |
| References |
| • |
Hayashi H, Okajima M, Yamada K: Atrial T (Ta) loop in dogs with or without atrial injury. Am Heart J. 1976 May;91(5):607-17.
[Pubmed]
|
| • |
Schran HF, Petryk L, Chang CT, O'Connor R, Gelbert MB: The pharmacokinetics and bioavailability of clemastine and phenylpropanolamine in single-component and combination formulations. J Clin Pharmacol. 1996 Oct;36(10):911-22.
[Pubmed]
|
|
| External Links |
|
|