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Pronunciation
(KLEM as teen)
Generic Available (U.S.)
Yes
Index Terms
Brand Names: U.S.
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Perennial and seasonal allergic rhinitis and other allergic symptoms including urticaria
Pregnancy Risk Factor
B
Lactation
Enters breast milk/not recommended
Contraindications
Hypersensitivity to clemastine or any component of the formulation; narrow-angle glaucoma
Warnings/Precautions
Concerns related to adverse effects:
• CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).
Disease-related concerns:
• Asthma: Use with caution in patients with a history of asthma.
• Cardiovascular disease: Use with caution in patients with cardiovascular disease (including hypertension and ischemic heart disease).
• Increased intraocular pressure: Use with caution in patients with increased intraocular pressure.
• Prostatic hyperplasia/urinary obstruction: Use with caution in patients with prostatic hyperplasia and/or GU obstruction.
• Pyloroduodenal obstruction: Use with caution in patients with pyloroduodenal obstruction (including stenotic peptic ulcer).
• Thyroid dysfunction: Use with caution in patients with thyroid dysfunction.
Concurrent drug therapy issues:
• Sedatives: Effects may be potentiated when used with other sedative drugs or ethanol.
Special populations:
• Elderly: Avoid use of this potent anticholinergic agent due to increased risk of confusion, dry mouth, constipation, and other anticholinergic effects; clearance decreases in patients of advanced age (Beers Criteria).
Adverse Reactions
Frequency not defined.
Cardiovascular: Palpitation, hypotension, tachycardia
Central nervous system: Dyscoordination, sedation, somnolence slight to moderate, sleepiness, confusion, restlessness, nervousness, insomnia, irritability, fatigue, headache, dizziness increased
Dermatologic: Rash, photosensitivity
Gastrointestinal: Diarrhea, nausea, xerostomia, epigastric distress, vomiting, constipation
Genitourinary: Urinary frequency, difficult urination, urinary retention
Hematologic: Hemolytic anemia, thrombocytopenia, agranulocytosis
Ocular: Blurred vision
Otic: Tinnitus
Respiratory: Thickening of bronchial secretions
Miscellaneous: Anaphylaxis
Metabolism/Transport Effects
Inhibits CYP2D6 (weak), CYP3A4 (weak)
Drug Interactions
Acetylcholinesterase Inhibitors (Central): Anticholinergics may diminish the therapeutic effect of Acetylcholinesterase Inhibitors (Central). Acetylcholinesterase Inhibitors (Central) may diminish the therapeutic effect of Anticholinergics. If the anticholinergic action is a side effect of the agent, the result may be beneficial. Risk C: Monitor therapy
Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Risk C: Monitor therapy
Amphetamines: May diminish the sedative effect of Antihistamines. Risk C: Monitor therapy
Anticholinergics: May enhance the adverse/toxic effect of other Anticholinergics. Exceptions: Levocabastine (Nasal); Paliperidone. Risk C: Monitor therapy
ARIPiprazole: CYP3A4 Inhibitors (Weak) may increase the serum concentration of ARIPiprazole. Management: Monitor for increased aripiprazole systemic exposure/affects with concomitant use of a weak CYP3A4 inhibitor. Decrease aripiprazole dose to 25% of the usual dose in patients receiving both a CYP3A4 and a CYP2D6 inhibitor (regardless of potencies). Risk C: Monitor therapy
ARIPiprazole: CYP2D6 Inhibitors (Weak) may increase the serum concentration of ARIPiprazole. Management: Monitor for increased aripiprazole pharmacologic effects. Aripiprazole dose adjustments may or may not be required based on concomitant therapy and/or indication. Consult product labeling for specific recommendations. Risk C: Monitor therapy
Benzylpenicilloyl Polylysine: Antihistamines may diminish the diagnostic effect of Benzylpenicilloyl Polylysine. Management: Suspend systemic H1 antagonists for benzylpenicilloyl-polylysine skin testing and delay testing until systemic antihistaminic effects have dissipated. A histamine skin test may be used to assess persistent antihistaminic effects. Risk D: Consider therapy modification
Betahistine: Antihistamines may diminish the therapeutic effect of Betahistine. Risk C: Monitor therapy
CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Exceptions: Levocabastine (Nasal). Risk C: Monitor therapy
Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (e.g., opioids, barbiturates) with concomitant use. Risk D: Consider therapy modification
Hyaluronidase: Antihistamines may diminish the therapeutic effect of Hyaluronidase. Management: Patients receiving antihistamines (particularly at larger doses) may not experience the desired clinical response to standard doses of hyaluronidase. Larger doses of hyaluronidase may be required. Risk D: Consider therapy modification
HydrOXYzine: May enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce adult dose of CNS depressant agents by 50% with initiation of concomitant methotrimeprazine therapy. Further CNS depressant dosage adjustments should be initiated only after clinically effective methotrimeprazine dose is established. Risk D: Consider therapy modification
Metyrosine: CNS Depressants may enhance the sedative effect of Metyrosine. Risk C: Monitor therapy
Pimozide: CYP3A4 Inhibitors (Weak) may increase the serum concentration of Pimozide. Risk X: Avoid combination
Pramlintide: May enhance the anticholinergic effect of Anticholinergics. These effects are specific to the GI tract. Risk D: Consider therapy modification
Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Ethanol: May increase CNS depression; monitor for increased effects with coadministration. Caution patients about effects.
Mechanism of Action
Competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract
Pharmacodynamics/Kinetics
Onset of action: Peak effect: Therapeutic: 5-7 hours
Duration: 8-12 hours; may persist for 24 hours
Absorption: Well absorbed
Distribution: Vd: ~800 L (range: 500-1000 L) (Sharma, 2003)
Metabolism: Hepatic; metabolized via unidentified enzymes by O-dealkylation followed by alcohol dehydration, aliphatic oxidation, aromatic oxidation, and direct oxidation; significant first-pass effect (Sharma, 2003)
Bioavailability: ~40% (Sharma, 2003)
Half-life elimination: ~21 hours (range: 10-33 hours) (Sharma, 2003)
Time to peak: 2-4 hours
Excretion: Urine (~42% as metabolites) (Sharma, 2003)
Dosage
Oral:
Infants and Children <6 years: 0.05 mg/kg/day as clemastine base or 0.335-0.67 mg/day clemastine fumarate (0.25-0.5 mg base/day) divided into 2 or 3 doses; maximum daily dosage: 1.34 mg (1 mg base)
Children 6-12 years: 0.67-1.34 mg clemastine fumarate (0.5-1 mg base) twice daily; do not exceed 4.02 mg/day (3 mg/day base)
Children ≥12 years and Adults:
1.34 mg clemastine fumarate (1 mg base) twice daily to 2.68 mg (2 mg base) 3 times/day; do not exceed 8.04 mg/day (6 mg base)
OTC labeling: 1.34 mg clemastine fumarate (1 mg base) twice daily; do not exceed 2 mg base/24 hours
Elderly: Lower doses should be considered in patients >60 years
Monitoring Parameters
Look for a reduction of rhinitis, urticaria, eczema, pruritus, or other allergic symptoms
Geriatric Considerations
Elderly patients may be more susceptible to adverse effects.
This medication is considered to be potentially inappropriate in this patient population (Beers Criteria: Quality of evidence - moderate; Strength of recommendation - strong).
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia (normal salivary flow resumes upon discontinuation).
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
Drowsiness is common; may cause nervousness; rare reports of depression
Mental Health: Effects on Psychiatric Treatment
Concurrent use with psychotropics may result in additive sedation
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Syrup, oral, as fumarate: 0.67 mg/5 mL (120 mL) [equivalent to clemastine base 0.5 mg/5 mL; prescription formulation]
Tablet, oral, as fumarate: 1.34 mg [equivalent to clemastine base 1 mg; OTC], 2.68 mg [equivalent to clemastine base 2 mg; prescription formulation]
Tavist® Allergy: 1.34 mg [scored; equivalent to clemastine base 1 mg]
Pricing: U.S. (www.drugstore.com)
Syrup (Clemastine Fumarate)
0.67 mg/5 mL (120): $18.99
Tablets (Clemastine Fumarate)
1.34 mg (100): $25.99
2.68 mg (30): $17.98
Tablets (Tavist Allergy)
1.34 mg (16): $17.99
References
American Academy of Pediatrics Committee on Drugs, “The Transfer of Drugs and Other Chemicals Into Human Milk,” Pediatrics, 2001, 108(3):776-89.
"American Geriatrics Society Updated Beers Criteria for Potentially Inappropriate Medication Use in Older Adults," J Am Geriatr Soc, 2012 [epub ahead of print].
Kok TH, Taitz LS, Bennett MJ, et al, “Drowsiness Due to Clemastine Transmitted in Breast Milk,” Lancet, 1982, 1:914-5.
Sharma A and Hamelin BA, "Classic Histamine H1 Receptor Antagonists: A Critical Review of Their Metabolic and Pharmacokinetic Fate from a Bird's Eye View," Curr Drug Metab, 2003, 4(2):105-29.
International Brand Names
Lexi-Comp.com
Last full review/revision April 2012
Content last modified April 2012
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