Diphenhydramine HCl

 Action Competitively antagonizes histamine at H1 receptor sites.

 Indications Symptomatic relief of perennial and seasonal allergic rhinitis, vasomotor rhinitis and allergic conjunctivitis; temporary relief of runny nose and sneezing caused by common cold; relief of allergic and nonallergic pruritic symptoms; treatment of urticaria and angioedema; amelioration of allergic reactions to blood or plasma; adjunct to epinephrine and other standard measures in anaphylaxis; relief of uncomplicated allergic conditions of immediate type when oral therapy is impossible or contraindicated (parenteral form); treatment and prophylactic treatment of motion sickness; nighttime sleep aid; management of parkinsonism (including drug-induced) in elderly who are intolerant of more potent agents, in mild cases in other age groups and in combination with centrally acting anticholinergics; control of cough from colds or allergy (syrup formulations).

 Contraindications Hypersensitivity to antihistamines; narrow-angle glaucoma; stenosing peptic ulcer; symptomatic prostatic hypertrophy; asthmatic attack; bladder neck obstruction; pyloroduodenal obstruction; MAOI therapy; history of sleep apnea; use in newborn or premature infants and in nursing women.

 Route/Dosage

Hypersensitivity Reactions, Type 1/Antiparkinsonism/Motion Sickness Adults: PO 25 to 50 mg q 4 to 6 hr (max, 300 mg/day). IV/IM 10 to 100 mg (rate not exceeding 25 mg/min or deep IM; max, 400 mg/day).

Children (6 to under 12 yr): PO 12.5 to 25 mg q 4 to 6 hr (max, 150 mg). IV/IM 5 mg/kg/day or 150 mg/m2 /day (max, 300 mg divided into 4 doses at a rate not exceeding 25 mg/min or deep IM).

Nighttime Sleep Aid Adults: PO 50 mg at bedtime.

Cough Suppressant (Syrup) Adults: PO 25 mg q 4 hr (max, 150 mg/24 hr).

Children (6 to 12 yr): PO 12.5 mg q 4 hr (max, 75 mg/24 hr).

Children (2 to 6 yr): PO 6.25 mg q 4 hr (max, 25 mg/24 hr).

 Interactions

Alcohol, CNS depressants: May cause additive CNS depression.

MAOIs: May increase anticholinergic effects.

Injectable form is incompatible with dexamethasone sodium phosphate, furosemide, iodipamide meglumine, parenteral barbiturates, and phenytoin.

 Lab Test Interferences

Skin tests: Antihistamines may prevent or diminish otherwise positive reaction to dermal reactivity indicators.

 Adverse Reactions

CARDIOVASCULAR: Orthostatic hypotension; palpitations; bradycardia; tachycardia; reflex tachycardia; extrasystoles; faintness. CNS: Drowsiness (often transient); sedation; dizziness; faintness; disturbed coordination.EENT: Nasal stuffiness; dry mouth, nose and throat; sore throat. GI: Epigastric distress; nausea; vomiting; diarrhea; constipation; change in bowel habits. HEMATOLOGIC: Hemolytic anemia; thrombocytopenia; agranulocytosis. METABOLIC: Increased appetite, weight gain. RESPIRATORY: Thickening of bronchial secretions; chest tightness; wheezing; respiratory depression. OTHER: Hypersensitivity reactions; photosensitivity.

 Precautions

Pregnancy: Category B. Lactation: Excreted in breast milk. Children: Contraindicated in newborn and premature infants. Overdosage may cause hallucinations, convulsions, and death. Antihistamines may diminish mental alertness. In young children drug may produce paradoxical excitation. Use with caution in children younger than 2 yr. Elderly and debilitated patients: Greater risk of dizziness, excessive sedation, syncope, toxic confusional states, and hypotension in patients older than 60 yr. Dosage reduction may be required. Special risk patients: Use with caution in patients predisposed to urinary retention, prostatic hypertrophy, history of bronchial asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease, or hypertension. Hepatic impairment: Use with caution in patients with cirrhosis or other liver diseases. Hypersensitivity reactions: May occur. Have epinephrine 1:1000 immediately available. Respiratory disease: Generally not recommended to treat lower respiratory tract symptoms including asthma. Sulfites: Some diphenhydramine products may contain sulfites as preservatives and aspartame as sweetener. Avoid in sulfite-allergic patients and in patients with phenylketonuria, respectively.

 Administration/Storage

• If patient is prone to excessive salivation (eg, postencephalitic patients), administer drug after meals. If mouth dries excessively, administer drug before meals.
• Syrup formulations are used only for control of cough.
• If drug is prescribed for motion sickness, administer first dose 30 min prior to exposure to motion.
• Give IM injection deep in muscle.
• Do not administer drug for at least 2 days before skin allergy testing.
• Store in tightly closed containers at room temperature.
• Store injection formulation in light-resistant container and protect from light.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Be alert for conditions that may place patient at greater risk for adverse effects (eg, bronchial asthma, glaucoma, prostatic hypertrophy).
• Be prepared to institute supportive treatment (eg, advanced life support) in event of severe adverse reaction or overdose.
• Observe patient for adverse reactions to medication such as dry mouth, headaches, disorientation, drowsiness, tachycardia, shortness of breath, nausea, skin rash, urinary retention, constipation, or increase in BP.
• If administering medication to children or elderly, be alert to fact that they are more likely to experience side effects and paradoxical reactions such as excitement, irritability, sleeplessness.
• Explain that drowsiness may occur at first but will lessen or disappear during long-term therapy.

 Patient/Family Education

• Instruct patient not to discontinue long-term therapy without consulting health care provider.
• Warn patient using topical medication to avoid excessive application to skin eruptions.
• Instruct patient to report these symptoms to health care provider: excessive drowsiness or dry mouth, GI upset, constipation, blurred vision, rash, hives, difficulty breathing, difficulty urinating, confusion, fainting, irregular heart rate.
• Encourage patient to take sips of water frequently, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.
• Instruct patient to avoid intake of alcoholic beverages or other CNS depressants.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.