Saturday, January 12, 2013


25 mg capsule, 50 mg capsule
12.5 mg/5 ml syrup

DRUG CATEGORY: Antihistamine

BRAND NAME: Benadryl®

Each 25 mg capsule contains 25 mg Diphenhydramine Hydrochloride.
Each 50 mg capsule contains 50 mg Diphenhydramine Hydrochloride.
Each 5ml contains 12.5 mg of Diphenhydramine Hydrochloride.

Diphenhydramine is 2-(diphenylmethoxy)-N,N-dimethylethylamine hydrochloride, and occurs as a white, crystalline powder, and is freely soluble in water and alcohol.

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.

ORAL: Diphenhydramine in the oral form is effective for the following indications.
  • ANTIHISTAMINIC: For perennial and seasonal (hay fever) allergic rhinitis; vasomotor rhinitis, allergic conjunctivis due to inhalant allergens and foods; 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 extrapyramidal reactions) 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.
Use in Newborn or Premature Infants: This drug should not be used in newborn or premature infants.
Use in Breastfeeding Mother: Because of the higher risk of antihistamines fro infants generally and for newborns and prematures in particular, antihistamine therapy is contraindicated in breastfeeding mothers. For pregnant women, consult your doctor before using this product.
Use in Lower Respiratory Disease: Antihistamine should NOT be used to treat lower respiratory tract symptom including asthma.
Antihistamines are also contraindicated in the following conditions: Hypersensitivity to diphenhydramine hydrochloride and other antihistamines of similar chemical structure; monoamine oxidase inhibitor therapy.

Antihistamines should be used with considerable caution in patients with narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, sympatomatic prostatic hypertrophy, or bladder-neck obstruction.
Use in Children: In infants and children, especially, antihistamine, in over-dosage 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 Pregnancy: Experience with this drug in pregnant women is inadequate to determine whether there exists a potential for harm to the developing fetus.
Use with CNS Depressants: Diphenhydramine hydrochloride has additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc.)
Use in activities requiring mental alertness: Patients should be warned about engaging in activities requiring mental alertness, such as driving a car or operating appliances, machinery, etc.
Use in the Elderly (approximately 60 years or older): 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 history of brochial asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease, or hypertension.

MAO inhibitors prolong and intensify the anticholinergic effects of antihistamines.

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 System: Hemolytic anemia, thrombocytopenis, agranulocytosis.
  4. Nervous System: Sedation, sleepiness, dizziness, disturbed coordination, fatique, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesia, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, hysteria, 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 and wheezing nasal stuffiness.

Antihistamine overdosage reactions may vary from central nervous system depression to stimulation. Stimulation is particularly likely in children. Atropine-like signs and symptoms like dry mouth, fixed dilated pupils; flushing and gastrointestinal symptoms may also occur. If vomiting has not occurred spontaneously, the patient should be induced to vomit. This the best done by having the patient drink a glass of water or milk, after which the patient should be mad to gag. Precautions against aspiration must be taken, especially in infants and children.
If vomiting is unsuccessful, gastric lavage is indicated within 3 hours after ingestion and even later if large amounts of milk or cream were given before hand.
Isotonic or ½ isotonic saline is the lavage solution of choice.
Saline cathartics, as milk or magnesia, by osmosis, draw water into the bowel and therefore are valuable for their action in rapid dilution of bowel content.
Stimulants should not be used.
Vasopressors may be used to treat hypotension.

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 is from 4 to 6 hours.
The usual adult dosage is 50 mg three or four times daily. Children (over 20 lbs): 12.5 to 25 mg, three or four times daily. Maximum daily dosage not to exceed 300 mg. Based upon body weight, the recommended dosage is 5 mg/kg/24 hours. In motion sickness, full dosage is recommended for prophylactic use, the first dose to be given 30 minutes before exposure to motion and similar doses before meals and upon retiring for duration of exposure.

Diphenhydramine hydrochloride should be stored at temperatures not exceeding 30oC and protected from light.

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