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Diphenhydramine Description

Diphenhydramine hydrochloride is an antihistamine drug having the chemical name 2-(Diphenylmethoxy)-N,N-dimethylethylamine hydrochloride. It occurs as a white, crystalline powder, is freely soluble in water and alcohol and has the molecular weight of 291.82. The molecular formula is C17H21NO•HCl. The structural formula is as follows:

Diphenhydramine hydrochloride injection is a sterile, pyrogen-free solution intended for I.M. or I.V. administration. Each mL contains 50 mg Diphenhydramine Hydrochloride, USP and sufficient hydrochloric acid and/or sodium hydroxide solution for pH adjustment (5.0–6.0). This product contains no antimicrobial preservative and is intended as a single use vial; once the unit is assembled and used, any remaining portion of the solution must be discarded with the entire unit.

Diphenhydramine - Clinical Pharmacology

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

Diphenhydramine hydrochloride in the injectable form has a rapid onset of action. Diphenhydramine hydrochloride is widely distributed throughout the body, including the CNS. A portion of the drug is excreted unchanged in the urine, while the rest is metabolized via the liver. Detailed information on the pharmacokinetics of Diphenhydramine hydrochloride injection is not available.

Indications and Usage for Diphenhydramine

Diphenhydramine hydrochloride in the injectable form is effective in adults and pediatric patients, other than premature infants and neonates, for the following conditions when Diphenhydramine in the oral form is impractical.

Antihistaminic

For amelioration of allergic reactions to blood or plasma, in anaphylaxis as an adjunct to epinephrine and other standard measures after the acute symptoms have been controlled, and for other uncomplicated allergic conditions of the immediate type when oral therapy is impossible or contraindicated.

Motion Sickness

For active treatment of motion sickness.

Antiparkinsonism

For use in parkinsonism, when oral therapy is impossible or contraindicated, as follows: parkinsonism in the elderly who are unable to tolerate more potent agents, mild cases of parkinsonism in other age groups, and in other cases of parkinsonism in combination with centrally acting anticholinergic agents.

Contraindications

Use in Neonates or Premature infants

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

Use in Nursing Mothers

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

Use as a Local Anesthetic

Because of the risk of local necrosis, this drug should not be used as a local anesthetic.

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.

Local necrosis has been associated with the use of subcutaneous or intradermal use of intravenous Diphenhydramine.

Use in Pediatric Patients

In pediatric patients, especially, antihistamines in overdosage may cause hallucinations, convulsions, or death.

As in adults, antihistamines may diminish mental alertness in pediatric patients. In the young pediatric patient, particularly, they may produce excitation.

Use in the 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 bronchial asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease or hypertension. Use with caution in patients with lower respiratory disease, including asthma.

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

Reproduction studies have been performed in rats and rabbits at doses up to 5 times the human dose an 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.

Pediatric Use

Diphenhydramine Hydrochloride Injection should not be used in neonates and premature infants (see CONTRAINDICATIONS).

Diphenhydramine Hydrochloride Injection may diminish mental alertness, or, in the young pediatric patient, cause excitation. Overdosage may cause hallucinations, convulsions, or death (see WARNINGS and OVERDOSAGE). See also DOSAGE AND ADMINISTRATION section.

Adverse Reactions

The most frequent adverse reactions are underscored.

1. General: Urticaria, drug rash, anaphylactic shock, photosensitivity, excessive perspiration, chills, dryness of mouth, nose, and throat
2. Cardiovascular System: Hypotension, headache, palpitations, tachycardia, extrasystoles
3. Hematologic: Hemolytic anemia, thrombocytopenia, agranulocytosis
4. 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
5. GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation
6. GU System: Urinary frequency, difficult urination, urinary retention, early menses
7. Respiratory System: Thickening of bronchial secretions, tightness of chest or throat and wheezing, nasal stuffiness.

Overdosage

Antihistamine overdosage reactions may vary from central nervous system depression to stimulation. Stimulation is particularly likely in pediatric patients. Atropine-like signs and symptoms, dry mouth; fixed, dilated pupils; flushing and gastrointestinal symptoms may also occur.

Stimulants should not be used.

Vasopressors may be used to treat hypotension.

Diphenhydramine Dosage and Administration

THIS PRODUCT IS FOR INTRAVENOUS OR INTRAMUSCULAR ADMINISTRATION ONLY.

Diphenhydramine hydrochloride in the injectable form is indicated when the oral form is impractical.

DOSAGE SHOULD BE INDIVIDUALIZED ACCORDING TO THE NEEDS AND THE RESPONSE OF THE PATIENT.

Pediatric Patients

Other than premature infants and neonates: 5 mg/kg/24 hr or 150 mg/m2/24 hr. Maximum daily dosage is 300 mg. Divide into four doses, administered intravenously at a rate generally not exceeding 25 mg/min, or deep intramuscularly.

Adults

10 to 50 mg intravenously at a rate generally not exceeding 25 mg/min, or deep intramuscularly; 100 mg if required; maximum daily dosage is 400 mg.

NOTE: Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

How is Diphenhydramine Supplied

Diphenhydramine Hydrochloride Injection, USP, 50 mg per mL, 1 mL vial.
In unit-use packages containing one single dose vial and a vial injector.
Twenty-five unit-use packages per carton.

Stock No. 1390      NDC 0548-1390-00      1 mL      21 G. × 1 1/2" Needle

Syringe Assembly Directions

USE ASEPTIC TECHNIQUE

Do not assemble until ready to use.

*CAUTION: IMPROPER ENGAGING MAY CAUSE GLASS BREAKAGE AND SUBSEQUENT INJURY.

Store at Controlled room temperature 15° to 30°C (59° to 86°F). Protect from light. Retain in carton until time of use.

Rx Only

INTERNATIONAL MEDICATION SYSTEMS, LIMITED

So. El Monte, CA 91733, U.S.A.
Amphastar Pharmaceuticals Company

Rev.7-00

6913900J

Revised: 05/2006