Diphenhydramine hydrochloride is the generic name (meaning it is not a brand name) for a medication that relieves allergy symptoms, hypersensitive reactions, motion sickness, and uncontrollable muscle movements. It also promotes sleepiness.
HOW DOES DIPHENHYDRAMINE HYDROCHLORIDE WORK?
Diphenhydramine hydrochloride works by blocking the effects a natural compound in the body, known as histamine, that is released during allergic reactions and leads to sneezing, watery eyes, itching, swelling, widening of blood vessels, increased heart rate, decreased blood pressure, increased secretions (release of substances) in the digestive system, and anaphalaxis (a severe, life threatening hypersensitivity to something one is allergic to). Although diphenhydramine hydrochloride decreases the amount and intensity of coughing, it does not eliminate the reflex to cough.
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Substances that block the effects of histamine are known as antihistamines (the Greek word "anti" means to "work against"). Diphenhydramine hydrochloride also reduces uncontrollable muscle movements by competing with the chemical messenger, acetylcholine, which contributes to muscle movements. Drugs that interfere with acetylcoline are described as anticholinergic. The word part "choline" in "anticholinergic" comes from "choline" in acetylcholine.
WHO TAKES DIPHENHYDRAMINE HYDROCHLORIDE?
Diphenhydramine hydrochloride is given to people who are experiencing allergic reactions, such as itchy skin, runny nose, cough, hives (types of skin eruptions), other skin rashes, and hay fever (allergic reactions to trees, grass, or weed pollens). Pollen is a dusty substance found in some plants that helps them reproduce. Because diphenhydramine hydrochloride causes sleepiness, it is also taken by people who are having difficulty sleeping. It is also given to relieve motion sickness and nausea, vomiting, and dizziness that is unrelated to motion sickness.
Some older patients with Parkinson's disease (a type of brain disorder that leads to serious difficulties with muscle movements), who cannot take stronger drugs for this condition, take diphenhydramine hydrochloride because it decreases muscle stiffness and tremors (uncontrollable shaking movements). Some younger patients with mild Parkinson's disease also take diphenhydramine hydrochloride. Because it helps control involuntary muscle movements, diphenhydramine hydrochloride is also given to patients who have developed involuntary movements as a side effect from another drug.
WHAT FORMS ARE DIPHENHYDRAMINE HYDROCHLORIDE AVAILABLE IN AND HOW SHOULD IT BE TAKEN?
Diphenhydramine hydrochloride is available in capsule form, tablet form, syrup form, injectable form (through a muscle or vein), cream form, gel form, stick form, spray form, and in an elixir (a clear, sweet, part-alcoholic liquid that is taken by mouth) form. It should be taken with milk or a meal to reduce stress on the digestive system. It is OK to remove the contents from the capsule and take it with water or food.
The skin should be cleaned before applying this medication on the skin in cream form or any other form that is rubbed on the skin. Do not apply this medication to exposed or blistered skin. If irritation occurs after using this drug, you should stop using it and contact your doctor.
WHAT ARE SIDE EFFECTS OF DIPHENHYDRAMINE HYDROCHLORIDE?
Common side effects of diphenhydramine hydrochloride are sleepiness, dry mouth, nausea, thickening of mucus, and anorexia (serious loss in body weight due to refusal to eat). Less common side effects are as follows: skin rash, rapid heartbeat, hypersensitivity reactions (such as to the light and sun), blurry vision, ringing in the ears, dizziness, headache, low blood pressure, diarrhea, difficult urination (peeing), painful urination, difficulty pooping (constipation), and confusion. There are no known special problems associated with long-term use of this drug.
DOES DIPHENHYDRAMINE HYDROCHLORIDE CAUSE BIRTH DEFECTS?
There are no known significant increases in birth defects associated with diphenhydramine hydrochloride in humans. However, the safety of this drug with pregnant women has not yet been determined. Animal studies have not found that birth defects are associated with this drug.
WHAT CAN I DO TO AVOID OR DECREASE DRY MOUTH THAT CAN OCCUR BY TAKING THIS DRUG?
To avoid dry mouth as a result of using diphenhydramine hydrochloride, it is recommended to take frequent sips of water or to use a sugarless gum and candy. Keeping your mouth clean by brushing your teeth regularly also helps. If dry mouth continues for more than 2 weeks, you should contact your doctor and/or your dentist.
WHO SHOULD NOT TAKE DIPHENHYDRAMINE HYDROCHLORIDE?
People with the following conditions should not take diphenhydramine hydrochloride: suddenly occurring attacks of asthma (difficulty breathing due to narrowing of the airway passage) and hypersensitivity to this drug. Moms who are secreting (releasing) breast milk should not take diphenhydramine hydrochloride because it passes into the breast milk. Children under age two should avoid this drug. People who cannot tolerate alcohol should also avoid this drug if it is taken in a form that includes alcohol, such as a syrup.
WHO SHOULD BE ESPECIALLY CAREFUL WHEN USING DIPHENHYDRAMINE HYDROCHLORIDE?
People who are elderly (over age 60) should be careful when using diphenhydramine hydrochloride because they are more likely to suffer side effects. It is recommended by many doctors that elderly patients take lower doses of this drug. Since the safety of diphenhydramine hydrochloride is not established during pregnancy, pregnant women should also be cautious before taking this medication.
People with the following medical conditions should also be careful when using diphenhydramine hydrochloride: severe breathing problems, severe liver disease, seizures (involuntary muscle movements due to overexcitement of nerve cells in the brain), or an enlarged prostate. The prostate is a gland near the bladder that produces a fluid that is part of semen. Semen is a fluid that is discharged from a male's penis in order to reproduce with a female.
People with narrow-angle glaucoma should also be careful when using diphenhydramine hydrochloride. Narrow-angle glaucoma is a sudden, painful condition in the eye as well as blurry vision caused by increased pressure that is due to a blockage of a watery fluid known as aqueous humor. You should contact your doctor for advice if you have any of the previously mentioned conditions.
WHAT PRECAUTIONS SHOULD BE TAKEN WITH DIPHENHYDRAMINE HYDROCHLORIDE?
Individuals taking diphenhydramine hydrochloride should avoid direct exposure to the sun and use sunscreen, since the body can become oversensitive to the effects of this drug when they are exposed to the sun. Alcohol and other substances that decrease the activity of the brain and spinal cord should also be avoided, since taking either of them with diphenhydramine hydrochloride can lead to negative reactions.
Driving, hazardous work, and other activities requiring alertness should be avoided when taking diphenhydramine hydrochloride, until you can assess how this drug affects you. Piloting an aircraft is not allowed when taking this drug.
HOW LONG DOES IT TAKE FOR DIPHENHYDRAMINE HYDROCHLORIDE TO WORK?
When taken by mouth, diphenhydramine hydrochloride works within 15 to 60 minutes. When injected through a muscle, it takes 20 to 30 minutes to work. When injected through a vein, it works rapidly.
HOW LONG DO THE EFFECTS OF DIPHENHYDRAMINE HYDROCHLORIDE LAST?
The effects of diphenhydramine hydrochloride work for approximately 4 to 8 hours, regardless of the form it is taken in.
WHEN SHOULD I STOP TAKING DIPHENHYDRAMINE HYDROCHLORIDE?
You should stop taking diphenhydramine hydrochloride if it is not effective after 5 days. You should also call your doctor at this point if the drug is not working.
HOW IS DIPHENHYDRAMINE HYDROCHLORIDE ABSORBED BY THE BODY?
Diphenhydramine hydrochloride is absorbed well by the body if one takes it by mouth or if it is injected through a muscle. However, it may not be absorbed well if taken as a cream or as another form that is rubbed on the skin.
Diphenhydramine hydrochloride is distributed widely throughout the body. It enters into the breast milk and crosses the placenta (an organ in a female that nourishes a baby during pregnancy). 95% of this drug is metabolized (chemically processed) by the liver.
DOES DIPHENHYDRAMINE HYDROCHLORIDE INTERACT WITH OTHER DRUGS OR FOODS?
Yes. This is why you should contact your doctor to see what you should do if you are taking other antihistamines, anticholinergics (drugs that reduce uncontrollable muscle movements by competing with the chemical messenger, acetylcholine), or central nervous system depressants (drugs that decrease the activity of the brain and/or spine). Using diphenhydramine hydrochloride with these drugs will further slow down certain bodily functions.
Diphenhydramine hydrochloride also interacts with disopyramide and quinidine(drugs used to control abnormal heart beat) as well as antidepressants known as tricyclics and MAO inhibitors. The interaction between diphenhydramine hydrochloride and these drugs makes side effects such as dry mouth and blurry vision worse.
Diphenhydramine hydrochloride can lead to excessive sleepiness when taken in combination with the following: 5-HTP (a chemical supplement believed to improve mood, sleep, pain, and decrease appetite), GABA (a chemical messenger in the body that sends messages telling it to slow down), kava (an herb believed to have calming effects), melatonin (a natural chemical in the body thought to promote sleep), melissa (leaves and flowers of a plant that is thought to have calming effects on the body), and valerian (an herb thought to help people sleep). Diphenhydramine hydrochloride is not known to interact with any foods.
WHAT IS THE USUAL DOSE FOR DIPHENHYDRAMINE HYDROCHLORIDE?
The dose of diphenhydramine hydrochloride that should be taken varies according to the reason for why this medication is being taken, the form in which the medication is taken, the age of the person, and the weight of the person. Following are the doses for diphenhydramine hydrochloride, according to these factors:
HAY FEVER SYMPTOMS (capsules, tablets, elixir, syrup):
Teenagers and adults: 25 to 50 milligrams (mg) very 4 to 6 hours.
Children weighing more than 20.02 pounds: 12.5 to 25 mg every 4 to 6 hours. The total dose per day should not be more than 300 mg a
Children weighing less than 20.02 pounds: 6.25 to 12.5 mg every 4 to 6 hours.
HAY FEVER SYMPTOMS (injection):
Adults: 10 to 50 mg through a vein or muscle, 2-3 times a day. A single dose may be as much as 100 mg, but the total dose per day
should not be more than 400 mg.
Children: 1.25 mg per 2.2 pounds (one kilogram) of body weight into a muscle four times a day. The total dose per day should not be more
than 300 mg.
HAY FEVER SYMPTOMS (cream, gel, or stick):
Adults and children 12 years or older: Apply cream, gel, or stick that says "2%," three to four times a day.
Children ages 6-12 years or older: Apply cream, gel, or stick that says "1%," three to four times a day.
COUGH (liquid form):
Adults and teenagers: 25 mg, every 4 to 6 hours, as needed. The total dose should not be more than 150 mg a day.
Children ages 2 to 6: 6.25 mg (half a teaspoon) every 4 to 6 hours. The total dose should not be more than 25 mg a day.
Children ages 6 to 12: 12.5 mg (1 teaspoon) to 25 mg (2 teaspoons) every 4 to 6 hours. The total dose should not be more than 75 mg a
NAUSEA, VOMITTING, AND DIZZINESS (capsules, tablets, elixir, syrup):
Adults: 25 to 50 mg every 4 to 6 hours.
Children: 1 to 1.5 mg per 2.2 pounds every 4 to 6 hours.
NAUSEA, VOMITTING, AND DIZZINESS (injection):
Adults: 10 mg through a vein or muscle. This may be increased to 25 to 50 mg every 2 to 3 hours.
Children: 1 to 1.5 mg per 2.2 pounds every 6 hours.
When using diphenhydramine hydrochloride to prevent motion sickness, it should be taken 30 minutes before traveling and 1 to 2 hours
before being exposed to anything that would lead to motion sickness, such as sitting on a boat before traveling on it.
PARKINSON'S DISEASE (capsules, tablets, elixir, syrup):
Adults: 25 mg, 3 times a day. The doctor may increase the dose slowly over time, but the total dose should not be more than 400 mg a
Children: 1.25 mg per 2.2 lbs into a muscle, four times a day. The total dose should not be more than 300 mg a day.
SLEEPING AND/OR RELAXATION DIFFICULTIES (capsules, tablets, elixir, syrup):
Adults: 50 mg, 20 to 30 minutes before going to bed.
For people who have occasional sleeping difficulties, this medication may be effective when taken only as needed (for example, only taking
it on the night one is having difficulty sleeping). For people with more serious sleeping problems, this medication may need to be taken on
a more regular basis. Such individuals should consult with their doctor to determine the length of time needed to take this medication or for
a possible change to another sleep medication.
WHAT IF I MISS A DOSE?
If you miss a dose of diphenhydramine hydrochloride, you should check with your doctor. Doctors generally recommend that you take it again as soon as you can. However, if this time is near your next scheduled dose, doctors generally recommend skipping the dose that was missed and not doubling the next dose.
WHAT ARE SYMPTOMS OF AN OVERDOSE OF DIPHENHYDRAMINE HYDROCHLORIDE AND WHAT SHOULD I DO?
Symptoms of an overdose of diphenhydramine hydrochloride include: being very sleepy, wide pupils (the black circle in the eyeball) that do not decrease in size in response to light, confusion, difficulty breathing, being excited easily, poor coordination, weak pulse, passing out, and seizures (involuntary muscle movements due to overexcitement of nerve cells in the brain). When an overdose occurs, the Emergency Medical Service (EMS) or the nearest poison control center should be called immediately. If in doubt of where to call, dial 911.
DOES DIPHENHYDRAMINE HYDROCHLORIDE INTERFERE WITH ANY LABARATORY TESTS?
Yes. If you are going to have your skin tested for an allergic reaction, then diphenhydramine hydrochloride can interfere with such a test. If this is the case, this medication should be stopped four days before taking such a skin test.
WHERE SHOULD DIPHENHYDRAMINE HYDROCHLORIDE BE STORED?
Diphenhydramine hydrochloride should be stored in a dry place and should be kept away from heat and direct light. Liquid forms should not be frozen.
WHAT ELSE IS DIPHENHYDRAMINE HYDROCHLORIDE KNOWN AS?
Diphenhydramine hydrochloride has been trademarked (given brand names) by several companies. These names are as follows: Allerdryl, AllerMax, Aller-med, Banophen, Beldin, Beldin Cough, Belix, Bena-D, Bena-D 50, Benadryl, Benadryl Itch Relief Children's, Benadryl Complete Allergy, Benadryl Dye-Free Allergy Medication, Benadryl Itch Stopping Gel Children's Formula, Benadryl Itch Stopping Gel Maximum Strength, Benahist, Ben-Allergin, Ben-Allergin 50, Benaphen, Benoject, Benylin Cough, Bydramine Cough, Compoz, Diahist, Dihydrex, Diphen-Cough, Diphenacen-10, Diphenacen, Diphenadryl, Diphenhist, Dormarex 2, Dormin, Fenylhist, Fynex, Genahist, Gen-D-Phen, Hydramine, Hydramyn, Hydril, Hyrexin, Hyrexin-50, Insomnal, Maximum Strength Benadryl Itch Relief, Miles Nervine, Nauzene Maximum Strength, Nervine Nighttime Sleep-Aid, Nidryl, Noradyl, Nordryl, Nordryl Cough, Nytol, Nytol Extra Strength, Nytol Maximum Strength, Nyto with DPH, Phendry, PMS-Diphenhydramine, Siladril, Silphen, Sleep-Eze D, Sleep-Eze D Extra Strength, Sleep-Eze 3, Sleepwell 2-nite, Sominex, Sominex Formula 2, Tusstat, Twilite, Uni-Bent Cough, Unisom SleepGels Maximum Strength, Valdrene, and Wehdryl.
Diphenhydramine hydrochloride can be purchased in your local drug store under one of the previously mentioned trademarked names. By law, the brand name versions of a generic drug all need to have the same ingredients as the generic version. The only difference between medications with brand names and those without brand names is the price.
WHY IS IT CALLED DIPHENHYDRAMINE HYDROCHLORIDE?
The chemical name for diphenhydramine hydrochloride is 2-(Diphenylmethoxy)-N,N-dimethylethylamine hydrochloride. By looking at the letters in purple, you can tell how diphenhydramine hydrochloride got its name.