Pharmacologic class: Histamine antagonist
Therapeutic class: Antihistamine
Pregnancy risk category C
Antagonizes effects of histamine at histamine1-receptor sites, but doesn't bind to or inactivate histamine. Also shows anticholinergic, antipruritic, and sedative activity.
Capsules (liquigels): 4 mg
Elixir: 2 mg/5 ml
Suspension: 12 mg/5 ml
Tablets: 4 mg, 8 mg, 12 mg
Tablets (extended-release): 8 mg, 12 mg
Indications and dosages
➣ Symptomatic relief of allergic symptoms caused by histamine release; severe allergic or hypersensitivity reactions
Adults and children ages 12 and older: 4 to 8 mg P.O. three to four times daily, or 8 to 12 mg extended-release tablets P.O. two or three times daily. Maximum dosage is 36 mg/day.
Children ages 6 to 12: 2 mg P.O. q 4 to 6 hours as needed, not to exceed 12 mg/day
Children ages 2 to 6: 1 mg P.O. q 4 to 6 hours p.r.n., not to exceed 6 mg/day
• Hypersensitivity to drug
• Coronary artery disease
• Urinary retention
• Pyloroduodenal obstruction
• Peptic ulcer
• MAO inhibitor use within past 14 days
Use cautiously in:
• angle-closure glaucoma, hepatic disease, hyperthyroidism, hypertension, bronchial asthma
• elderly patients
• pregnant patients.
• Give with food if GI upset occurs.
• Don't break or crush extended-release tablets.
• Shake oral suspension well before measuring dose.
☞ Check elixir and suspension doses carefully, because the mg/ml varies widely between the two liquids.
CNS: drowsiness, sedation, dizziness, excitation, irritability, syncope, tremor
CV: hypertension, hypotension, palpitations, tachycardia, extrasystole, arrhythmias, bradycardia
EENT: blurred vision, nasal congestion or dryness, dry or sore throat
GI: nausea, vomiting, constipation, dry mouth
GU: urinary retention or hesitancy, dysuria, early menses, decreased libido, impotence
Hematologic: hemolytic anemia, hypoplastic anemia, thrombocytopenia, agranulocytosis, leukopenia, pan-cytopenia
Respiratory: thickened bronchial secretions, chest tightness, wheezing
Skin: urticaria, rash
Other: increased or decreased appetite, weight gain
Drug-drug. CNS depressants (including opioids and sedative-hypnotics): additive CNS depression
MAO inhibitors: intensified, prolonged anticholinergic effects
Drug-diagnostic tests. Allergy tests: false results
Granulocytes, platelets: decreased counts
Drug-behaviors. Alcohol use: increased CNS depression
• Monitor respiratory status.
• Stay alert for urinary retention, urinary frequency, and painful or difficult urination. Discontinue drug if these problems occur.
• With long-term use, monitor CBC.
• Monitor elderly patient for dizziness, sedation, and hypotension.
• If patient takes over-the-counter antihistamines, monitor him closely to avoid potential overdose.
• Advise patient to take drug with meals if GI upset occurs.
• Instruct patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• Caution patient to avoid alcohol while taking drug.
• Urge patient to tell all prescribers which drugs and over-the-counter preparations he's taking.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.