Dosing & Uses
Dosage Forms & Strengths
tablet
- 4mg
oral solution
- 2mg/5mL
Hypersensitivity Reaction
4 mg PO q8hr initially; maintenance: 4-20 mg/day, up to 32 mg/day divided q8hr in some patients; not to exceed 0.5 mg/kg/day
Spasticity Associated With Spinal Cord (Off-label)
2-4 mg PO q8hr initially; not to exceed 24 mg/day
Migraine Headache Prophylaxis (Off-Label)
2 mg PO q12hr with or without propanol
Decreased Appetite Secondary to Chronic Disease (Off-label)
2 mg PO q6hr for one week; THEN 4 mg PO q6hr
Drug-Induced Sexual Dysfunction (Off-label)
4-12 mg PO 1-2 hours before anticipated coitus or 1-16 mg/day
Serotonin Syndrome (Off-Label)
12 mg initially PO, followed by 2 mg q2hr or 4-8 mg PO q6hr as needed to control symptoms
Dosing Modifications
Nonanticholinergic antihistamines should be considered first when treating allergic reactions (Beers Criteria)
Advanced age is associated with reduced clearance and greater risk of confusion, dry mouth, constipation, and other anticholinergic effects and toxicity; use lower end of dosage range (4 mg PO q12hr) for elderly patients, or administer less frequently
Renal impairment: Elimination is reduced in renal insufficiency; administer lower doses, and monitor closely
Dosage Forms & Strengths
tablet
- 4mg
oral solution
- 2mg/5mL
Hypersensitivity Reaction
<2 years old: Safety and efficacy not established
2-6 years old: 2 mg PO q8-12hr; not to exceed 12 mg/day
7-14 years old: 4 mg PO q8-12hr; not to exceed 16 mg/day
Alternatively, total daily dose of 0.25 mg/kg or 8 mg/m²
Migraine
Prophylaxis
< 3 years: Safety and efficacy not established
>3 years and adolescents: 0.2-0.4 mg/kg/day PO divided BID; not to exceed 0.5 mg/kg/day
Loss of Appetite (Including Anorexia Nervosa; Off-label)
Stimulation of appetite
<13 years: Safety and efficacy not established
>13 years: 2 mg PO q6hr initially; increased to up to 8 mg q6hr over 3 weeks
Dosing Modifications
Renal impairment: Elimination is reduced in renal insufficiency; administer lower doses, and monitor closely
Interactions
Interaction Checker
No Results
Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor
Adverse Effects
Frequency Not Defined
Psychiatric/neurologic: CNS depression, drowsiness, sedation ranging from mild drowsiness to deep sleep (most frequent), dizziness, lassitude, disturbed coordination; less commonly, restlessness, insomnia, tremors, euphoria, nervousness, irritability, delirium, seizures, toxic psychosis, paresthesia
Muscular: Weakness
Cardiovascular: Palpitation, tachycardia, palpitation, ECG changes (eg, widened QRS), arrhythmias (eg, extrasystole, heart block), hypotension, hypertension, dizziness, sedation, hypotension
GI: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation
Hepatic: Cholestasis, hepatitis, hepatic failure, hepatic function abnormality, jaundice (rare)
Skin: Eczema, pruritus, inflammation, papular rash, erythema on exposed skin
Sensory: Visual disturbances, blurred vision, diplopia, tinnitus, acute labyrinthitis
Renal: Dysuria, urinary retention
Respiratory: Thickening of bronchial secretions, wheezing, nasal stuffiness
Other: Vertigo, sweating, chills, early menses, headache, impotence, dryness of mouth, nose, and throat, facial dyskinesia, tightness of chest, faintness
Warnings
Contraindications
Documented hypersensitivity
Premature infants and neonates
Nursing women
Concomitant monoamine oxidase inhibitor therapy
Narrow-angle glaucoma
Stenosing peptic ulcer, pyloroduodenal obstruction
Symptomatic prostatic hypertrophy
Bladder neck obstruction
Elderly, debilitated patients
Cautions
Elimination reduced in renal insufficiency
Use with caution in cardiovascular disease, including hypertension
Elderly patients: Avoid use in elderly because of high incidence of anticholinergic effects; may exacerbate existing lower urinary conditions or benign prostatic hyperplasia; if used, administer at low end of dosage range
May cause CNS depression, which may impair mental abilities; use caution when operating heavy machinery
Use caution in cardiovascular disease, including hypertension and ischemic heart disease
Use with caution in patients with increased intraocular pressure, history of asthma or other chornic breathing disorders, or thyroid dysfunction
Nonanticholinergic antihistamines should be considered first for treatment of allergic reaction in the elderly (Beers criteria)
Antihistamines may cause excitation in young children
Pregnancy & Lactation
Pregnancy category: B
Lactation: Excretion in milk unknown; contraindicated
Pregnancy Categories
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Pharmacology
Mechanism of Action
Serotonin and histamine antagonist; competitively inhibits H1 receptor, mediating bronchial constriction, smooth-muscle contraction, edema, hypotension, CNS depression, and cardiac arrhythmias; prevents histamine release in blood vessels and is more effective in preventing histamine response than in reversing it; may be useful in patients with syndromes sustained by histamine-producing tumors
Moderate anticholinergic activity with low sedative effect
May have anti-5HT2 effects
May have some calcium-channel blocking activity
Absorption
Peak plasma time: 6-9 hr
Metabolism
Metabolized by glucuronidation via UGT1A
Metabolites: Quaternary ammonium glucuronide conjugate
Elimination
Excretion: Urine (40%), feces (2-20%)
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Patient Handout
Formulary
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