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Pharmacologic class: Piperidine (nonselective)
Therapeutic class: Antihistamine
Pregnancy risk category B
Antagonizes effects of histamine at histamine1-receptor sites, preventing histamine-mediated responses. Also blocks effects of serotonin, causing increased appetite.
Syrup: 2 mg/5 ml
Tablets: 4 mg
Indications and dosages
➣ Allergy symptoms caused by histamine release (including seasonal and perennial allergic rhinitis); chronic urticaria; angioedema; dermographism; cold urticaria; adjunctive therapy for anaphylactic reactions
Adults: Initially, 4 mg P.O. q 8 hours. Maintenance dosage is 4 to 20 mg/day in three divided doses, to a maximum dosage of 0.5 mg/kg/day.
Children ages 7 to 14: 2 to 4 mg P.O. q 12 hours. Don't exceed 16 mg/day.
Children ages 2 to 6: 2 mg P.O. q 12 hours. Don't exceed 12 mg/day.
• Vascular cluster headaches
• Anorexia nervosa
• Cushing's syndrome
• Hypersensitivity to drug
• Alcohol intolerance (syrup only)
• Bladder neck obstruction
• Angle-closure glaucoma
• Ulcer disease
• Symptomatic prostatic hypertrophy
• MAO inhibitor use within past 14 days
Use cautiously in:
• hepatic impairment
• elderly patients
• pregnant patients (safety not established)
• breastfeeding patients.
• Give with food or milk to decrease GI upset.
CNS: drowsiness, dizziness, excitation (especially in children), fatigue, sedation, hallucinations, disorientation, tremor
CV: palpitations, hypotension, arrhythmias
EENT: blurred vision, nasal dryness and congestion, dry throat
GI: constipation, dry mouth
GU: urinary retention, urinary frequency, ejaculatory inhibition, early menses
Respiratory: thickened bronchial secretions
Skin: rash, photosensitivity
Other: weight gain
Drug-drug. CNS depressants (including opioid analgesics, sedative-hypnotics): increased CNS depression
MAO inhibitors: intensified, prolonged anticholinergic effects
Drug-diagnostic tests. Allergy skin tests: false-negative reactions
Drug-behaviors. Alcohol use: increased CNS depression
• Monitor patient for excessive anti-cholinergic effects.
• Assess for excessive CNS depression.
• Discontinue drug 4 days before diagnostic skin testing.
• Advise patient to take drug with food to minimize GI upset.
• Caution patient not to use other CNS depressants, sleep aids, or alcohol during therapy.
• Instruct patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.