DIPHENHYDRAMINE HYDROCHLORIDE
INJECTION, USP

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 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.

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.

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.

For active treatment of motion sickness.

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.

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

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

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

Hypersensitivity to diphenhydramine hydrochloride and other antihistamines of similar chemical structure.

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.

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.

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

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.

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.

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.

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

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.

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: 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 or throat and wheezing, nasal stuffiness.

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.

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.

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.

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.

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

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.