clemastine

Absorption: Well absorbed following oral administration.

Distribution: Enters breast milk in high concentrations.

Metabolism/Excretion: Extensively metabolized by the liver.

Half-Life: Unknown.

Time/Action Profile ⬆ ⬇

(antihistaminic effects)

ROUTE	ONSET	PEAK	DURATION
PO	15–60 min	1–2 hr	8–16 hr

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
Angle-closure glaucoma;
Known alcohol intolerance (liquid form);
Lactation: Lactation.

Use Cautiously in:

Acute asthma attacks;
Liver disease;
Prostatic hyperplasia;
Hyperthyroidism;
Hypertension;
OB: 2nd-generation antihistamines are preferred in pregnancy;
Pedi: Children 6 yr (safety and effectiveness not established);
Geri: Older adults are more susceptible to adverse reactions.

Adv. Reactions/Side Effects ⬆ ⬇

CV: hypertension, arrhythmias, hypotension, palpitations, tachycardia

Derm: rash

EENT: blurred vision

GI: dry mouth, GI obstruction, constipation, nausea, vomiting

GU: urinary retention

Neuro: drowsiness, paradoxical excitation (children), confusion, dizziness

Resp: thick mucus

Interactions ⬆ ⬇

Drug-drug:

Additive CNS depression with other CNS depressants, including alcohol, opioid analgesics, and sedative/hypnotics.
May antagonize effects of cholinergic agonists (e.g. donepezil).

Drug-Natural Products:

Concomitant use of kava-kava, valerian, skullcap, chamomile, or hops can ↑ CNS depression.

Route/Dosage ⬆ ⬇

PO (Adults ): OTC labeling: 1.34 mg (1 mg base) twice daily. Rx labeling: 1.34 mg (1 mg base) twice daily; may increase up to 2.68 mg (2 mg base) 3 times daily.
PO (Children 6–12 yr): 0.67–1.34 mg (0.5–1 mg base) twice daily. (not to exceed 4.02 mg/day (3 mg/day base).

Availability ⬆ ⬇

(Generic available)

Tablets: 2.68 mg (2 mg base)
Syrupcitrus flavor: 0.67 mg/5 mL (0.67 mg clemastine fumarate = 0.5 mg base) (contains 5.5% alcohol)

Assessment ⬆ ⬇

Assess allergy symptoms (rhinitis, conjunctivitis, hives, urticaria) prior to and periodically during therapy.
Assess lung sounds and character of bronchial secretions. Maintain fluid intake of 1500–2000 mL/day to decrease viscosity of secretions.

Lab Test Considerations:

May cause false-negative reactions on allergy skin tests; discontinue 3 days prior to testing.

Toxicity and Overdose:

Symptoms of toxicity in children include excitement, hyperreflexia, hallucinations, tremors, ataxia, fever, seizures, fixed dilated pupils, dry mouth, and facial flushing. The dose that causes seizures approximates the lethal dose. Adults are more likely to experience severe drowsiness.

Implementation ⬆ ⬇

PO: Administer with food or milk to decrease GI irritation.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take medication as directed. Do not take more than recommended amount. Take missed doses as soon as possible unless almost time for next dose. Do not double doses.
May cause drowsiness. Caution patient to avoid driving or other activities requiring alertness until response to drug is known.
Caution patient to avoid using alcohol or other CNS depressants, including opioids, concurrently with this drug.
Advise patient that good oral hygiene, frequent rinsing of mouth with water, and sugarless gum or candy may help relieve dry mouth. Patient should notify dentist if dry mouth persists for >2 wk.
Geriatric patients are at risk for orthostatic hypotension. Advise patient to change positions slowly.
Instruct patient to contact health care professional if symptoms persist or if difficulty with urination; changes in vision; confusion; severe dry mouth, nose, and throat; or dizziness occurs. May be more common in geriatric patients. Parents should notify health care professional if their child has difficulty sleeping, becomes unusually excited or irritable, or develops shortness of breath or facial flushing.
Rep: May cause fetal harm. Advise females of reproductive potential to avoid taking clemastine during pregnancy and breastfeeding and to notify health care professional if pregnancy is planned or suspected.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇