Diphenhydramine Hydrochloride (diphenhydramine hydrochloride 50 mg) Dailymed

Revised MAY 1999

1000590101

Rx only

Description:

Diphenhydramine Hydrochloride is an antihistamine drug having the chemical name 2-(diphenylmethoxy)-N, N-dimethylethylamine hydrochloride. It occurs as a white, odorless crystalline powder and is freely soluble in water and alcohol. The structural formula is as follows:
C₁₇H₂₁NO • HCl Molecular Weight: 291.82
Each capsule contains 50 mg of diphenhydramine hydrochloride for oral administration.

Inactive Ingredients:

Anhydrous lactose, lactose monohydrate and magnesium stearate.

The 50 mg capsule shell contains D&C red no. 28, FD&C blue no. 1, FD&C red no. 40, gelatin, silicon dioxide and sodium lauryl sulfate.

The imprinting ink contains D&C yellow no. 10 aluminum lake, FD&C blue no. 1 aluminum lake, FD&C blue no. 2 aluminum lake, FD&C red no. 40 aluminum lake, pharmaceutical glaze, propylene glycol and synthetic black iron oxide.

Clinical Pharmacology:

Diphenhydramine hydrochloride is an antihistamine with anticholinergic (drying) and sedative effects. Antihistamines appear to compete with histamine for cell receptor sites on effector cells.

A single oral dose of diphenhydramine hydrochloride is quickly absorbed with maximum activity occurring in approximately one hour. The duration of activity following an average dose of diphenhydramine hydrochloride is from four to six hours. Diphenhydramine is widely distributed throughout the body, including the CNS. Little, if any, is excreted unchanged in the urine; most appears as the degradation products of metabolic transformation in the liver, which are almost completely excreted within 24 hours.

Indications And Usage:

Diphenhydramine hydrochloride in the oral form is effective for the following indications:

Antihistaminic:

For allergic conjunctivitis due to foods; mild, uncomplicated allergic skin manifestations of urticaria and angioedema; amelioration of allergic reactions to blood or plasma; dermatographism; as therapy for anaphylactic reactions adjunctive to epinephrine and other standard measures after the acute manifestations have been controlled.

Motion Sickness:

For active and prophylactic treatment of motion sickness.

Antiparkinsonism:

For parkinsonism (including drug-induced) in the elderly unable to tolerate more potent agents; mild cases of parkinsonism (including drug-induced) in other age groups; in other cases of parkinsonism (including drug-induced) in combination with centrally acting anticholinergic agents.

Nighttime sleep-aid.

Contraindications:

Use in Newborn or Premature Infants:

This drug should not be used in newborn or premature infants.

Use in Nursing Mothers:

Because of the higher risk of antihistamines for infants generally, and for newborns and prematures in particular, antihistamine therapy is contraindicated in nursing mothers.

Antihistamines are also contraindicated in the following conditions: Hypersensitivity to diphenhydramine hydrochloride and other antihistamines of similar chemical structure.

Warnings:

Antihistamines should be used with considerable caution in patients with narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, symptomatic prostatic hypertrophy, or bladder-neck obstruction.

Use in Children:

In infants and children, especially, antihistamines in overdosage may cause hallucinations, convulsions, or death.

As in adults, antihistamines may diminish mental alertness in children. In the young child, particularly, they may produce excitation.

Use in Elderly (approximately 60 years or older):

Antihistamines are more likely to cause dizziness, sedation, and hypotension in elderly patients.

Precautions:

General:

Diphenhydramine hydrochloride has an atropine-like action and therefore should be used with caution in patients with a history of lower respiratory disease including asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease or hypertension.

Information for Patients:

Patients taking diphenhydramine hydrochloride should be advised that this drug may cause drowsiness and has an additive effect with alcohol.

Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc.

Drug Interactions:

Diphenhydramine hydrochloride has additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc).

MAO inhibitors prolong and intensify the anticholinergic (drying) effects of antihistamines.

Carcinogenesis, Mutagenesis, Impairment of Fertility:

Long-term studies in animals to determine mutagenic and carcinogenic potential have not been performed.

Pregnancy:

Pregnancy Category B:

Reproduction studies have been performed in rats and rabbits at doses up to 5 times the human dose and have revealed no evidence of impaired fertility or harm to the fetus due to diphenhydramine hydrochloride. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Adverse Reactions:

The most frequent adverse reactions are underscored.

• General: Urticaria, drug rash, anaphylactic shock, photosensitivity, excessive perspiration, chills, dryness of mouth, nose and throat.
• Cardiovascular System: Hypotension, headache, palpitations, tachycardia, extrasystoles.
• Hematologic System: Hemolytic anemia, thrombocytopenia, agranulocytosis.
• Nervous System: Sedation, sleepiness, dizziness, disturbed coordination, fatigue, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesia, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, neuritis, convulsions.
• GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation.
• GU System: Urinary frequency, difficult urination, urinary retention, early menses.
• Respiratory System: Thickening of bronchial secretions, tightness of chest and wheezing, nasal stuffiness.