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Pronunciation:

(KLEM as teen)

U.S. Brand Names:

Dayhist® Allergy [OTC]; Tavist® Allergy [OTC]

Synonyms:

Clemastine Fumarate

Generic Available:

Yes

Use:

Perennial and seasonal allergic rhinitis and other allergic symptoms including urticaria

Pregnancy Risk Factor:

Lactation:

Enters breast milk/not recommended

Contraindications:

Hypersensitivity to clemastine or any component of the formulation; narrow-angle glaucoma

Warnings/Precautions:

Safety and efficacy have not been established in children <6 years of age. Use caution with bladder neck obstruction, symptomatic prostate hypertrophy, asthmatic attacks, stenosing peptic ulcer, increased intraocular pressure, hyperthyroidism, cardiovascular disease, hypertension, and in the elderly. May cause drowsiness; use caution in performing tasks which require alertness.

Adverse Reactions:

Frequency not defined.

Cardiovascular: Palpitations, hypotension, tachycardia

Central nervous system: Dyscoordination, sedation, slight to moderate somnolence, sleepiness, confusion, restlessness, nervousness, insomnia, irritability, fatigue, headache, increased dizziness

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

Overdosage/Toxicology:

Symptoms of overdose include anemia, metabolic acidosis, hypotension, hypothermia

There is no specific treatment for an antihistamine overdose, however, most of its clinical toxicity is due to anticholinergic effects. For anticholinergic overdose with severe life-threatening symptoms, physostigmine 1-2 mg (0.5 mg or 0.02 mg/kg for children) I.V., slowly may be given to reverse these effects.

Drug Interactions:

Inhibits CYP2D6 (weak), 3A4 (weak)

Increased toxicity (CNS depression): CNS depressants, MAO inhibitors, tricyclic antidepressants, phenothiazines

Ethanol/Nutrition/Herb Interactions:

Ethanol: Avoid ethanol (may increase CNS depression).

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: 8-16 hours

Absorption: Almost complete

Metabolism: Hepatic

Excretion: Urine

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

Patient Education:

Avoid alcohol; may cause drowsiness, may impair coordination or judgment

Nursing Implications:

Raise bed rails, institute safety measures, assist with ambulation

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:

Syrup, as fumarate [prescription formulation]: 0.67 mg/5 mL (120 mL) [0.5 mg base/5 mL; contains alcohol 5.5%; citrus flavor]

Tablet, as fumarate: 1.34 mg [1 mg base; OTC], 2.68 mg [2 mg base; prescription formulation]

Dayhist® Allergy, Tavist® Allergy: 1.34 mg [1 mg base]

International Brand Names:

Agasten® (BR); Alagyl® (JP); Alergosan® (YU); Benanzyl® (JP); Clamist® (IN); Clemanil® (JP); Clemastin® (BG, RO); Clemastinum® (PL); Fuluminol® (JP); Inbestan® (JP); Kinotomin® (JP); Lacretin® (JP); Mallermin-F® (JP); Marsthine® (JP); Masletine® (JP); Piloral® (JP); Tavegil® (DE, ES, GB, IT, LU, NL); Tavegyl® (AT, BG, CH, CO, CZ, DK, EG, HU, ID, JO, KW, LB, MT, NO, PT, RO, RU, SE, SI, TR, ZA); Tavist® (MX); Telgin-G® (JP); Xolamin® (JP)

References

"American Academy of Pediatrics Committee on Drugs. The Transfer of Drugs and Other Chemicals Into Human Milk,"Pediatrics, 2001, 108(3):776-89.

Kok TH, Taitz LS, Bennett MJ, et al, "Drowsiness Due to Clemastine Transmitted in Breast Milk,"Lancet, 1982, 1:914-5.

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