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Benadryl Injection (Diphenhydramine Injection): Side Effects, Uses, Dosage, Interactions, Warnings

Benadryl Injection

Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 10/18/2023

Drug Summary

What Is Benadryl Injection?

Benadryl Injection (diphenhydramine hydrochloride) is an antihistamine used to treat life-threatening allergic reactions (anaphylaxis) along with epinephrine and other treatments. Benadryl Injection is also used to relieve symptoms of household allergies, hay fever and the common cold when medication cannot be given by mouth. Benadryl Injection is also used to treat nausea, vomiting and dizziness caused by motion sickness when medication cannot be given by mouth. The brand name of Benadryl Injection is discontinued, but generic versions may be available.

What Are Side Effects of Benadryl Injection?

Benadryl Injection may cause serious side effects including:

  • mood changes,
  • restlessness,
  • confusion,
  • pounding or irregular heartbeat,
  • ringing in the ears,
  • seizure, and
  • difficulty urinating

Get medical help right away, if you have any of the symptoms listed above.

Common side effects of Benadryl Injection (diphenhydramine hydrochloride) include:

  • drowsiness,
  • dizziness,
  • headache,
  • irritability,
  • stomach upset,
  • vision changes (e.g., blurred vision),
  • decreased coordination, or
  • dry mouth/nose/throat.

Tell your doctor right away if you have any serious side effects of Benadryl Injection including mental/mood changes (such as restlessness, confusion), pounding or irregular heartbeat, ringing in the ears, seizures, or difficulty urinating.

Seek medical care or call 911 at once if you have the following serious side effects:

  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheadedness, or passing out;
  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors.

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

Dosage for Benadryl Injection

The adult dose of Benadryl Injection is 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.

What Drugs, Substances, or Supplements Interact with Benadryl Injection?

Benadryl Injection may interact with antihistamines applied to the skin, antispasmodics, drugs for Parkinson's disease, MAO inhibitors, antidepressants, or drugs that cause drowsiness (such as antihistamines, anti-seizure drugs, medicine for sleep or anxiety, muscle relaxants, narcotics, or psychiatric medicines). Tell your doctor all medications and supplements you use.

Benadryl Injection During Pregnancy and Breastfeeding

During pregnancy, Benadryl Injection should be used only if prescribed. This drug passes into breast milk and may have undesirable effects on a nursing infant. Consult your doctor before breastfeeding.

Additional Information

Our Benadryl Injection (diphenhydramine hydrochloride) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

Description for Benadryl Injection

Benadryl (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 a molecular weight of 291.82. The molecular formula is C17H21NO • HCl, and structural formula:

Benadryl in the parenteral form is a sterile, pyrogen-free solution available in a concentration of 50 mg of diphenhydramine hydrochloride per mL. The solutions for parenteral use have been adjusted to a pH between 5.0 and 6.0 with either sodium hydroxide or hydrochloric acid. The multidose Steri-Vials® contain 0.1 mg/mL benzethonium chloride as a germicidal agent.

Uses for Benadryl Injection

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

Dosage for Benadryl Injection

THIS PRODUCT IS FOR INTRAVENOUS OR INTRAMUSCULAR ADMINISTRATION ONLY.

Benadryl in the injectable form is indicated when the oral form is impractical.

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

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.

HOW SUPPLIED

Benadryl in parenteral form is supplied as:

Benadryl Steri-Vials®

-sterile, pyrogen-free solution containing 50 mg diphenhydramine hydrochloride in each milliliter of solution with 0.1 mg/mL benzethonium chloride as a germicidal agent. Available in 10-mL (NDC 0071-4402-10) Steri-Vials.

-sterile, pyrogen-free solution containing 50 mg diphenhydramine hydrochloride in each milliliter of solution. Available in packages of twenty-five 1 mL (NDC 0071-4259-13) Steri-Vials.

Benadryl Steri-Dose®

-sterile, pyrogen-free solution containing 50 mg diphenhydramine hydrochloride in a 1-mL disposable syringe (Steri-Dose). Available in packages of ten syringes (NDC 0071-4259-45).

Benadryl Ampoule

-sterile, pyrogen-free solution containing 50 mg diphenhydramine hydrochloride in a 1-mL ampoule. Available in packages of ten (NDC 0071-4259-03).

Store at controlled room temperature 15°-30°C (59°-86°F). Protect from freezing and light.

Rx only

Side Effects for Benadryl Injection

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 or throat and wheezing, nasal stuffiness

Drug Interactions for Benadryl Injection

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.

Warnings for Benadryl Injection

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 Benadryl.

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 for Benadryl Injection

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

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.

Pediatric Use

Benadryl should not be used in neonates and premature infants (see CONTRAINDICATIONS).

Benadryl may diminish mental alertness, or, in the young pediatric patient, cause excitation. Overdosage may cause hallucinations, convulsions, or death (see WARNINGS, OVERDOSAGE, and DOSAGE AND ADMINISTRATION sections).

Overdose Information for Benadryl Injection

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.

Contraindications for Benadryl Injection

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.

Clinical Pharmacology for Benadryl Injection

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.

Benadryl 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.

Patient Information for Benadryl Injection

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.

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