Classifications: antihistamine (h1-receptor antagonist);
Therapeutic: antihistamine
; h1-receptor antagonist
Prototype: Diphenhydramine
Pregnancy Category: B


1.34 mg, 2.68 mg tablets; 0.67 mg/5 mL syrup


An antihistamine (H1-receptor antagonist) that competes for H1-receptor sites on effector cells, thus blocking histamine effectiveness. Has greater selectivity for peripheral H1-receptors and, consequently, it produces little sedation. Has prominent antipruritic activity and low incidence of unpleasant adverse effects.

Therapeutic Effect

Effective in controlling various allergic reactions (e.g., nasal congestion, sneezing, itching).


Symptomatic relief of allergic rhinitis (sneezing, rhinorrhea, pruritus) and mild uncomplicated allergic skin manifestations such as urticaria and angioedema.


Hypersensitivity to clemastine or to other antihistamines of similar chemical structure; lower respiratory tract symptoms, including acute asthma; concomitant MAO INHIBITOR therapy; closed angle glaucoma; children <6 y; lactation.

Cautious Use

History of bronchial asthma, COPD; increased intraocular pressure; GI or GU obstruction; hyperthyroidism; hepatic disease; cardiovascular disease, hypertension, older adults; children, pregnancy (category B).

Route & Dosage

Allergic Rhinitis
Adult: PO 1.34 mg b.i.d., may increase up to 8.04 mg/d
Child: PO >6 y, 0.67 mg b.i.d., may increase up to 4.02 mg/d; <6 y, 0.335–0.67 mg/kg/d in 2 divided doses (max: 1.34 mg/d)

Allergic Urticaria
Adult: PO 2.68 mg b.i.d. or t.i.d., may increase up to 8.04 mg/d
Child: PO 1.34 mg b.i.d., may increase up to 4.02 mg/d


  • Drug may be administered with food, water, or milk to reduce possibility of gastric irritation.
  • Older adult patients usually require less than average adult dose.
  • Store at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

Body as a Whole: Anaphylaxis, excess perspiration, chills. CV: Hypotension, palpitation, tachycardia, extrasystoles. GI: Dry mouth, epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation. Hematologic: Hemolytic anemia, thrombocytopenia, agranulocytosis. CNS: Sedation, transient drowsiness, dry nose and throat, headache, dizziness, weakness, fatigue, disturbed coordination; confusion, restlessness, nervousness, hysteria, convulsions, tremors, irritability, euphoria, insomnia, paresthesias, neuritis. Respiratory: Dry nose and throat, thickening of bronchial secretions, tightness of chest, wheezing, nasal stuffiness. Skin: Urticaria, rash, photosensitivity. Special Senses: Vertigo, tinnitus, acute labyrinthitis, blurred vision, diplopia. Urogenital: Difficult urination, urinary retention, early menses.


Drug: Alcohol and other cns depressants increase sedation; mao inhibitors may prolong and intensify anticholinergic effects.


Absorption: Readily from GI tract. Peak: 5–7 h. Duration: 10–12 h. Distribution: Into breast milk. Metabolism: In liver. Elimination: In urine.

Nursing Implications

Assessment & Drug Effects

  • Monitor for drowsiness, poor coordination, or dizziness, especially in the older adult or debilitated. Supervision of ambulation may be warranted.
  • Assess for symptomatic relief with use of the medication.
  • Lab tests: Periodic hematological studies with long-term use.

Patient & Family Education

  • Check with physician before taking alcohol or other CNS depressants, since effects may be additive.
  • Clemastine may cause lethargy and drowsiness; therefore, necessary safety precautions should be taken.
  • Older adults should make position changes slowly and in stages, particularly from recumbent to upright posture, as dizziness and hypotension occur more frequently than in younger patients.
  • Avoid driving and other potentially hazardous activities until response to the drug has been established.
  • Frequent sips of water or sugarless hard candy to relieve dry mouth.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 02/01/2023 (0)
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