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P-I-E-N-O Drug Brand Name,
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diphenhydramine/ BenadrylTM , DiphedrylTM
ANTIHISTAMINE/anticholinergic
Description: Diphenhydramine
is an antihistamine of the ethanolamine class. Ethanolamine
antihistamines have significant antimuscarinic activity and
produce marked sedation in most patients. In general,
gastrointestinal side effects are minimal. Diphenhydramine is a
popular antihistamine due to its relative safety after parenteral
administration. In addition to the usual allergic symptoms, the
drug also treats irritant cough, although the drying effect may
be counterproductive. Diphenhydramine is effective in the relief
of nausea, vomiting, and vertigo associated with motion sickness.
It also is used commonly to treat drug-induced extrapyramidal
symptoms as well as to treat mild cases of Parkinson's disease.
Diphenhydramine was originally approved by the FDA in 1946 as a
prescription-only drug but was later changed to OTC status. Due
to its ability to induce drowsiness, it is also promoted as an
OTC hypnotic.
Mechanism of Action: Rather
than preventing the release of histamine, as do cromolyn and
nedocromil, diphenhydramine competes with free histamine for
binding at HA-receptor sites. Diphenhydramine competitively
antagonizes the effects of histamine on HA-receptors in the GI
tract, uterus, large blood vessels, and bronchial muscle. (Continues below video)
Antihistamines also possess anticholinergic
properties in varying degrees; ethanolamine derivatives have
greater anticholinergic activity than do other antihistamines,
which probably accounts for the antidyskinetic action of
diphenhydramine. This anticholinergic action appears to be due to
a central antimuscarinic effect, which also may be responsible
for its antiemetic effects, although the exact mechanism is
unknown. Diphenhydramine has a direct suppressive action on the
cough center and causes sedation via CNS depression. Topical
diphenhydramine provides local relief from insect bites, minor
burns, sunburn, or minor abrasions, possibly due to an anesthetic
effect resulting from decreased permeability of nerve cell
membranes to sodium ions (preventing the transmission of nerve
impulses). Following prolonged administration of diphenhydramine,
tolerance can occur, but this may be beneficial because of
reduced sedative effects.
Pharmacokinetics: In general,
antihistamines are well absorbed from the GI tract, but different
antihistamines vary in solubility, which affects the onset of
action. Less soluble antihistamines have a slower onset of action
and are less likely to cause toxicity. Onset of action of
diphenhydramine occurs in about 15-30 minutes, with peak
concentration occurring in about 2-4 hours. The duration of
action ranges from 4-6 hours. Diphenhydramine is highly
protein-bound. It is widely distributed in body tissues and
fluids, and it crosses the placenta and is excreted into breast
milk.
Metabolism occurs in the liver to produce
diphenylmethoxyacetic acid, which may be conjugated; other
metabolites are also formed. Plasma half-life is between 2-8
hours. Excretion, consisting of unchanged drug and metabolites,
is primarily renal and occurs within 24-48 hours of dosage.
CONTRAINDICATIONS/PRECAUTIONS:
Diphenhydramine is relatively contraindicated in patients with
asthma and COPD, especially during acute attacks, because
anticholinergic actions may thicken secretions and reduce
expectoration.
Diphenhydramine is classified as pregnancy
category C. Antihistamines generally are not recommended for use
in pregnancy, especially during the third trimester, because
there is a risk of seizures in the fetus. Risks-benefits should
be considered during pregnancy and in women expecting to become
pregnant. Antihistamines are contraindicated for use in women who
are breast-feeding because they can induce hyperexcitability in
the infant, seizures in premature infants, and inhibited
lactation. Alternative methods of feeding are recommended if
diphenhydramine therapy is deemed necessary.
Diphenhydramine should be used with extreme
caution in children. Children can experience paradoxical CNS
stimulation and should be supervised in their activities to
ensure safety. Some children have experienced respiratory
depression and sleep apnea while taking antihistamines; SIDS has
occurred. The drug should be used with extreme caution in
children with a family history of SIDS or sleep apnea.
Antihistamines are contraindicated in neonates because they may
experience paradoxical CNS stimulation and there is an increased
risk of seizures.
Diphenhydramine should be used with extreme
caution in patients predisposed to or with closed-angle glaucoma.
Due to its anticholinergic actions, it can increase intraocular
pressure, precipitating an acute attack of glaucoma.
Diphenhydramine must also be used cautiously in patients with
open-angle glaucoma; glaucoma therapy may need to be adjusted.
Diphenhydramine should be used cautiously in
patients with hepatic disease. Diphenhydramine is extensively
metabolized in the liver, hepatic impairment may lead to a
decrease in metabolism, a subsequent increase in drug levels, and
an added risk of toxicity.
Because of anticholinergic effects,
diphenhydramine should be used with extreme caution in patients
with bladder obstruction, GI obstruction, prostatic hypertrophy,
or urinary retention. Antihistamines have a quinidine-like action
as well as anticholinergic action, and should be used with
caution in patients with cardiac disease because they can cause
tachycardia, palpitations, and/or arrhythmias.
Diphenhydramine should be used with caution in
patients with hyperthyroidism or hypertension since it can
exacerbate these conditions.
Antihistamines should be used with caution in
patients undertaking tasks requiring mental alertness. Drowsiness
can be severe in some patients. Adverse effects are more likely
to occur in geriatric patients. Patients should exercise extreme
caution until the effects are known. Alcohol can add to sedation
caused by diphenhydramine.
In addition, antihistamines can mask signs of
allergic reactions, thus delaying the diagnosis of a
hypersensitivity reaction.
DRUG INTERACTIONS: If
diphenhydramine is used concomitantly with other CNS depressants,
additive CNS effects, such as drowsiness and sedation, can occur.
Patients taking diphenhydramine should be warned not to
self-medicate with with ethanol; barbiturates; anxiolytics,
sedatives, and hypnotics; or other HA-blockers.
MAOIs can increase and prolong anticholinergic
and CNS depressant effects of diphenhydramine. Their concurrent
use is not recommended.
Other drugs that have anticholinergic activity
can add to the anticholinergic side effects of diphenhydramine.
These drugs include tricyclic antidepressants, direct
anticholinergics, and phenothiazines. Diphenhydramine often is
used to treat extrapyramidal symptoms associated with
phenothiazine or butyrophenone therapy.
Diphenhydramine administered with
thyrotropin-releasing hormone, TRH can increase serum amylase and
prolactin concentrations.
ADVERSE REACTIONS: CNS
depression, manifested as drowsiness, sedation, and/or dizziness,
can occur during therapy with diphenhydramine. There is
considerable individual patient response to sedative effects, so
patients should be warned of the possible impairment of mental
acuity. These side effects may disappear after a few days of
medication. Geriatric patients may be more disposed to adverse
CNS depressant effects, and alcohol intake will increase
sedation. If symptoms persist or are severe, a dose reduction or
switch to another antihistamine may be advisable. Other possible
CNS effects include headache and hallucinations.
Antihistamines sometimes can cause CNS
stimulation. This effect is more likely to occur in children with
overdoses, and symptoms may include restlessness or akathisia,
insomnia, palpitations, and seizures.
Diphenhydramine possesses a moderate degree of
anticholinergic actions. Anticholinergic effects that can occur
during therapy include thickening of bronchial secretions,
xerostomia, urinary retention, insomnia, nervousness, dysuria,
and/or blurred vision. Geriatric patients are more likely to
experience such adverse reactions.
Antihistamines may cause adverse GI effects
including nausea/vomiting, diarrhea, constipation, abdominal
pain, and/or anorexia. Some of these adverse reactions may be
relieved by taking the drug with meals or milk.
Adverse cardiovascular responses are likely to
be associated with the anticholinergic properties or the
quinidine-like anesthetic effects of antihistamines. These
responses can include sinus tachycardia, extrasystoles,
palpitations, and/or cardiac arrhythmias. Alpha-adrenergic
blockade can lead to symptoms of hypotension. Hypertension can
also occur.
Topically application of diphenhydramine can
result in a hypersensitivity reaction. Allergic contact
dermatitis has been reported and is manifested by inflammation,
pruritus, and eczema.
PATIENT INFORMATION:
What do diphenhydramine tablets or capsules do?
Diphenhydramine (BenadrylTM ) is an
antihistamine that has many uses. It relieves irritant cough,
symptoms of hay fever (allergic rhinitis), hives (rash or
itching), and other allergic reactions, motion sickness and
vertigo (dizziness and loss of balance), and Parkinson's disease.
Generic diphenhydramine tablets or capsules are available, with
or without a prescription.
What should my doctor, dentist or pharmacist
know before I take diphenhydramine?
They need to know if you have any of these
conditions:
- asthma or congestive lung disease
- glaucoma high blood pressure or heart
disease
- liver disease
- other chronic illness
- prostate trouble
- pain or difficulty passing urine
- thyroid disease
- ulcers or other stomach problems
- an unusual or allergic reaction to
diphenhydramine, other medicines foods, dyes, or
preservatives
- pregnant or trying to get pregnant
- breast-feeding
How should I take this medicine?
Take diphenhydramine tablets or capsules by
mouth. Follow the directions on the prescription label. Take
diphenhydramine with food or milk if it upsets your stomach. Take
your doses at regular intervals. Do not take your medicine more
often than directed.
If you are taking diphenhydramine to stop you
getting car (or travel) sick, take the first dose 30 to 60
minutes before you leave.
Special precautions for use in
children:
Diphenhydramine is not for
children under 6 years old, unless prescribed by the doctor.
What if I miss a dose?
If you miss a dose, take it as soon as you can.
If it is almost time for your next dose, take only that dose. Do
not take double doses.
What other medicines can interact with
diphenhydramine?
- alcohol
- barbiturate medicines for inducing sleep
or treating seizures (convulsions)
- medicines for anxiety or sleeping
problems, such as diazepam or temazepam
- medicines for hay fever and other
allergies
- medicines for mental depression
- medicines for mental problems and
psychotic disturbances
- medicines for movement
abnormalities as in Parkinson's disease, or for
gastrointestinal problems
- thyrotropin-releasing hormone
Tell your doctor or pharmacist: about all other
medicines you are taking, including non-prescription medicines;
if you are a frequent user of drinks with caffeine or alcohol; if
you smoke; or if you use illegal drugs. These may affect the way
your medicine works. Check before stopping or starting any of
your medicines.
What side effects may I notice from taking
diphenhydramine?
Serious side effects with diphenhydramine
include:
- agitation, nervousness, excitability, not
able to sleep (these are more likely in children)
- blurred vision
- dizziness or fainting spells
- irregular heartbeat, palpitations, or
chest pain
- muscle or facial twitches
- pain or difficulty passing urine
- seizures (convulsions)
Call your doctor as soon as you can if you get
any of these.
Minor side effects with diphenhydramine
include:
- drowsiness, dizziness
- dry mouth
- headache
- loss of appetite
- stomach upset, nausea, vomiting,
constipation or diarrhea
Let your doctor know about these side effects
if they do not go away or if they annoy you.
What do I need to watch for while I take
diphenhydramine?
Tell your doctor if your symptoms do not
improve in 1 or 2 days.
You may get drowsy or dizzy. Do not drive, use
machinery, or do anything that needs mental alertness until you
know how diphenhydramine affects you. To reduce the risk of dizzy
or fainting spells, do not stand or sit up quickly, especially if
you are an older patient. Alcohol may increase dizziness and
drowsiness. Avoid alcoholic drinks.
Your mouth may get dry. Chewing sugarless gum
or sucking hard candy, and drinking plenty of water will help.
Where can I keep my medicine?
Keep out of the reach of children in a
container that small children cannot open.
Store at room temperature, between 15 and 30C
(59 and 86F). Protect from moisture. Keep container tightly
closed. Throw away any unused medicine after the expiration date.
The P-I-E-N-O Parkinsn's List Drug Database Index
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