Diphenhydramine is an antihistamine used in psychiatric medicine to treat phenothiazine drug-induced abnormal muscle movement. It is also used in general medicine to treat allergies, allergic reactions, motion sickness, insomnia , cough, and nausea. When diphenhydramine is used for allergy-related symptoms, it is sold in the United States as an over-the-counter medication Benadryl. For use in the treatment of the tremors caused by phenothiazines, diphenhydramine is prescribed in the generic form.
Some drugs called phenothiazines are used to treat psychotic disorder such as schizophrenia . As a side effect, these drugs may cause tremors and abnormal involuntary movements of the muscles, referred to as extrapyramidal neurologic movement disorders . Diphenhydramine is used to control these symptoms. Other uses of the drug include the treatment of nausea, vomiting, and itching. Diphenhydramine is used to help limit allergic reactions to transfused blood products. It can induce sleep. It is sometimes used to treat the stiffness and tremor of Parkinson's disease. In liquid form, it may relieve minor throat irritation.
Diphenhydramine is an antihistamine that is readily distributed throughout the body. It is easily absorbed when taken by mouth. Maximal action occurs approximately one hour after swallowing the drug. The effects continue for four to six hours. Diphenhydramine acts on cells in the brain . It seems to compete with the chemical histamine for specific receptor sites on cells in the brain and central nervous system. This means that it achieves its theraputic effect by taking the place of the neurotransmitter histamine on these cells. Diphenhydramine is a useful medication for individuals with mild Parkinsonism when it is used in combination with centrally acting anticholinergic drugs.
The dosage of diphenhydramine must be adjusted according to the needs of individuals and their responses. Adults are generally given 25–50 mg orally, three to four times daily. Diphenhydramine may be administered through a vein or injected deep within a muscle. The usual dosage is 10–50 mg per injection, although some people may require 100 mg. The total daily dosage should not exceed 400 mg. People who forget to take a dose of this drug should skip the dose and take the next one at the regularly scheduled time. They should not double up subsequent doses if one is missed.
People should not take diphenhydramine if they are taking other preparations that contain antihistamines unless specifically directed to do so by a physician.
People with peptic ulcer disease, bowel obstructions, an enlarged prostate, angle closure glaucoma, or difficulty urinating due to a blockage in the bladder should not use diphenhydramine without close physician supervision and monitoring. People with asthma, heart disease, high blood pressure, or an overactive thyroid should use this drug with caution. Before taking diphenhydramine, people with these conditions should discuss the risks and benefits of this drug with their doctor. Individuals should not take diphenhydramine for several days before an allergy test, as it will interfere with accurate results.
Elderly people are more sensitive to the sedating effects of diphenhydramine. The drug may also cause dizziness and lower blood pressure. Older people should slowly change position from sitting or lying to standing while taking this medication to prevent dizziness and fainting.
Drowsiness commonly occurs after taking diphenhydramine. This effect may be more pronounced if alcohol or any other central nervous system depressant, such as a tranquilizer or a particular medication for pain, is also taken. People taking the drug should not drive, or operate machinery, or perform hazardous tasks requiring mental alertness until the effects of the medication have worn off. In some people, diphenhydramine also may cause dizziness, difficulties with coordination, confusion, restlessness, nervousness, difficulty sleeping, blurry or double vision, ringing in the ears, headache, or convulsions.
Stomach distress is a relatively common side effect of diphenhydramine. Some people may develop poor appetites, nausea, vomiting, diarrhea, or constipation. Individuals also may experience low blood pressure, palpitations, rapid or irregular heartbeats, frequent urination, or difficulty urinating. Urine may be retained in the bladder. Other side effects of diphenhydramine are associated with persons in age groups that are unlikely to use the drug.
Diphenhydramine may also cause hives, a rash, sensitivity to the sun, and a dry mouth and nose. Thickened lung secretions are common among older persons.
Alcohol, pain medications, sleeping pills, tranquilizers, and antidepressants may make the drowsiness associated with diphenhydramine more severe. Diphenhydramine should not be used by persons taking hay fever medicines, sedatives, narcotics, anesthetics, barbiturates or muscle relaxants.
Adams, Michael and Norman Holland. Core Concepts in Pharmacology. Philadelphia: Lippincott-Raven, 1998.
Foreman, John C. and Torben Johansen. Textbook of Receptor Pharmacology. 2nd ed. Boca Raton, FL: CRC Press, 2002.
Page, Clive P., and Michael Murphy. Integrated Pharmacology. St. Louis: Mosby-Year Book, 2002.
Von Boxtel, Chris J., Budiono Santoso, and I. Ralph Edwards. Drug Benefits and Risks: International Textbook of Clinical Pharmacology. New York: John Wiley and Sons, 2001.
Agostini J. V., L. S. Leo-Summers, S. K. Inouye. "Cognitive and other adverse effects of diphenhydramine use in hospitalized older patients." Archives of Internal Medicine (2001) 161, no. 17: 2091-2097.
Cox D., Z. Ahmed, and A. J. McBride. "Diphenhydramine dependence." Addiction (2001) 96, no. 3: 516-517.
Vinson D. R., and D. L. Drotts. "Diphenhydramine for the prevention of akathisia induced by prochlorperazine: a randomized, controlled trial." Annals of Emergency Medicine (2001) 37, no. 2: 125-131.
American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211-2672. Telephone: (913) 906-6000. Web site: <http://www.aafp.org>.
American College of Physicians. 190 N Independence Mall West, Philadelphia, PA 19106-1572. Telephone: (800) 523-1546, x2600 or (215) 351-2600. Web site: <http://www.acponline.org>.
American Parkinson Disease Association, Inc. 1250 Hylan Boulevard, Suite 4B, Staten Island, NY 10305-1946. Telephone: (800) 223-2732 or (718) 981-8001. FAX: (718) 981-4399. Web site: <http://www.apdaparkinson.com>.
American Psychiatric Association. 1400 K Street NW, Washington, DC 20005. Telephone: (888) 357-7924. FAX (202) 682-6850.
American Society for Clinical Pharmacology and Therapeutics. 528 North Washington Street, Alexandria, VA 22314. Telephone: (703) 836-6981. Fax: 703-836-5223.
American Society for Pharmacology and Experimental Therapeutics. 9650 Rockville Pike, Bethesda, MD 20814-3995. Telephone: (301) 530-7060.
Parkinson's Disease Foundation. 710 West 168th Street, New York, NY 10032-9982. Telephone: (800) 457-6676 or (212) 923-4700. FAX: (212) 923-4778. Web site: <http://www.pdf.org>.
L. Fleming Fallon, Jr., M.D., Dr.P.H.
"Diphenhydramine." Gale Encyclopedia of Mental Disorders. . Encyclopedia.com. (April 29, 2017). http://www.encyclopedia.com/psychology/encyclopedias-almanacs-transcripts-and-maps/diphenhydramine
"Diphenhydramine." Gale Encyclopedia of Mental Disorders. . Retrieved April 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/psychology/encyclopedias-almanacs-transcripts-and-maps/diphenhydramine
Diphenhydramine is an antihistamine, used to treat allergies, motion sickness, allergic reactions, insomnia, cough, nausea, and phenothiazine drug-induced abnormal muscle movement.
Diphenhydramine is frequently ordered for cancer patients to aid in controlling nausea and itching . It may be given after a blood transfusion to limit allergic reactions to blood products. Because of its sedating properties, diphenhydramine is often used to assist in inducing sleep. It is also used to control nausea, treat the stiffness and tremor of Parkinson's disease, and control symptoms of extrapyramidal neurologic movement disorders (tremors and abnormal involuntary movements of the muscles) caused by some drugs used to treat psychosis or nausea and vomiting ). The drug may also be formulated as a syrup and used to relieve a cough caused by minor throat irritation due to a cold or hay fever.
Diphenhydramine is an antihistamine that dries, sedates, and is distributed throughout the body. It is readily absorbed when taken by mouth, with peak action occurring about one hour after ingestion. The effects last from four to six hours. This type of drug seems to compete with histamine for receptor sites after exposure to an allergen. By blocking histamine from attaching to the receptor site, the drug decreases itchiness, a runny nose, hives, and other symptoms of an allergic reaction.
The dose should be adjusted depending on the needs of the patient and their response to the medication. Adults generally take from 25 mg to 50 mg, three to four times daily. For sleep, 50 mg at bedtime is the usual dose. Injectable diphenhydramine, 10 mg to 50 mg, may be administered through a vein or injected deep within a muscle. Some patients may require 100 mg injections. The daily dose should not exceed 400 mg. Patients should not double up on doses if one is missed.
Children weighing more than 20 pounds may take from 12.5 mg to 25 mg, three to four times daily. Children should not consume more than 300 mg in one day. The doctor may calculate a recommended dosage based on the child's weight. Parents should not double up on doses if one is missed.
Lotions or creams with diphenhydramine may be applied to the skin to relieve itching in adults and children older than two. The creams contain 1% or 2% diphenhydramine and may be used on the affected area three to four times per day. Topical diphenhydramine should not be applied to large areas of the body, blistered or oozing skin, sunburn, or lesions caused by poison ivy or chicken-pox. Patients should not use topical diphenhydramine with other antihistamine-containing lotions or creams.
Patients with angle closure glaucoma, peptic ulcer disease, bowel obstructions, an enlarged prostate, or difficulty urinating due to a blockage in the bladder should not use this medication without a doctor's order and monitoring. This drug should be used with caution in patients with asthma, heart disease, high blood pressure, or an overactive thyroid. Prior to taking this medication, patients with these conditions should discuss this medication with their doctor. Patients should not take diphenhydramine for several days prior to an allergy test. It will interfere with obtaining accurate results.
Elderly patients are prone to diphenhydramine's sedating effects. The drug may also cause dizziness and lower blood pressure in this population group. Patients should slowly change position from sitting or lying to standing when taking this medication.
Children also may experience drowsiness. In young children, this drug may produce the opposite effect. Pregnant women and those breast feeding should discuss the use of this and other drugs with their physician prior to use.
Drowsiness commonly occurs after taking diphenhydramine. This effect may be more pronounced if alcohol or another central nervous system depressant, such as a tranquilizer or pain medication, is also ingested. Those taking the drug should refrain from driving or operating machinery or appliances until the medication has worn off. It also may cause dizziness, coordination difficulties, confusion, restlessness, nervousness, difficulty sleeping, blurry or double vision, ringing in the ears, headache, or convulsions.
Stomach distress also is common with diphenhydramine. Patients may develop a poor appetite, nausea and vomiting , diarrhea or constipation. Patients also may experience low blood pressure, palpitations, a rapid or irregular heart beat, an early onset of menstruation, frequent urination, or difficulty urinating, with urine retained in the bladder.
Diphenhydramine may also cause hives, a rash, sensitivity to the sun, and a dry mouth and nose. Thickened lung secretions are common.
Alcohol, pain medications, sleeping pills, tranquilizers and antidepressants may make the drowsiness associated with diphenhydramine more severe.
Diphenhydramine's drying effects may be stronger and last longer when taken with an antidepressant called an MAO inhibitor.
Debra Wood, RN
—Something that triggers an allergic reaction
—Agent that blocks or counteracts the action of histamine
Extrapyramidal movement disorders
—Involuntary movements that occur as a side effect of psychiatric medications
—Substance released during allergic reaction
"Diphenhydramine." Gale Encyclopedia of Cancer. . Encyclopedia.com. (April 29, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/diphenhydramine
"Diphenhydramine." Gale Encyclopedia of Cancer. . Retrieved April 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/diphenhydramine