Transcript Antihistamine effect

Topics
Lilley
Respiratory
35 & 36
Anti TB
40
Antihistamines, Decongestants,
Antitussives, and Expectorants
 Viral
infection
• (rhinovirus or influenza virus)
• Virus invades(mucosa) of upper respiratory tract
 Inflammatory
response
• Virus invades(mucosa) of upper respiratory tract
 Results
in:
• Excessive mucus production
 Fluid drips down the pharynx into the esophagus and
lower respiratory tract,
 Cold symptoms: sore throat, coughing, upset stomach
• Sneeze reflex
 Irritation of nasal mucosa often triggers the sneeze
reflex
• Nasal congestion –
 Release of inflammatory and vasoactive substances,
 dilating small blood vessels in the nasal sinuses and causing
nasal congestion

Combined use of antihistamines, nasal decongestants,
antitussives, and expectorants

Treatment is symptomatic only, not curative

Symptomatic treatment does not eliminate the causative pathogen

Difficult to identify whether cause is viral or bacterial

Treatment is “empiric therapy,” treating the most likely cause

Antivirals and antibiotics may be used, but a definite viral or
bacterial cause may not be easily identified
Compete with histamine for specific receptor
sites

Two histamine receptors
• H1 (histamine1)
H1 antagonists commonly referred to as antihistamines
Antihistamines have several properties
 Antihistaminic
 Anticholinergic
 Sedative
• H2 (histamine2)
 H2 blockers or H2 antagonists
 Used to reduce gastric acid in peptic ulcer disease
 10%
to 20% of general population is
sensitive to various environmental allergies
 Histamine-mediated disorders
• Allergic rhinitis (hay fever, mold, and dust allergies)
• Anaphylaxis
• Angioneurotic edema
• Drug fevers
• Insect bite reactions
• Urticaria (itching)
 Mechanism
of Action:
• Block action of histamine at the H1 receptor sites
• Compete with histamine for binding at unoccupied
receptors
 The binding of H1 blockers to the histamine receptors
prevents the adverse consequences of histamine
stimulation
 Vasodilation
 Increased GI and respiratory secretions
 Increased capillary permeability

Mechanism of Action
Cannot push histamine off the receptor if already
bound
• More effective in preventing the actions of histamine rather
than reversing them
• Should be given early in treatment, before all the histamine
binds to the receptors
Cardiovascular (small blood vessels)

Histamine effects
• Dilation and increased permeability
(allowing substances to leak into tissues)

Antihistamine effects
• Reduce dilation of blood vessels
• Reduce increased permeability of blood vessels
Smooth muscle (on exocrine glands)

Histamine effects
• Stimulate salivary, gastric, lacrimal, & bronchial secretions

Antihistamine effects
• Reduce salivary, gastric, lacrimal, and
bronchial secretions
Immune system (release of substances commonly
associated with allergic reactions)

Histamine effects
• Mast cells release histamine and other substances, resulting in
allergic reactions

Antihistamine effect
• Binds to histamine receptors, thus preventing histamine from causing
a response
Skin



Reduce capillary permeability, wheal-and-flare formation, itching
Anticholinergic
• Drying effect that reduces nasal, salivary, and lacrimal gland
secretions (runny nose, tearing, and itching eyes)
Sedative
• Some antihistamines cause drowsiness
Management of:
Nasal allergies
 Seasonal or perennial allergic rhinitis
(hay fever)
 Allergic reactions
 Motion sickness
 Parkinson’s disease
 Sleep disorders
 Relieve symptoms associated with the common cold

• Sneezing, runny nose
• Palliative treatment, not curative
 Anticholinergic
(drying) effects, most
common
• Dry mouth
• Difficulty urinating
• Constipation
• Changes in vision
 Drowsiness
• Mild drowsiness to deep sleep
 Traditional
• Older
• Work both peripherally and centrally
• Have anticholinergic effects, making them more effective than nonsedating drugs in some cases
 diphenhydramine (Benadryl);
 chlorpheniramine (Chlor-Trimeton)
 Non-sedating/peripherally acting
• Developed to eliminate unwanted adverse effects, mainly
sedation
• Work peripherally to block the actions of histamine
 fewer CNS adverse effects
• Longer duration of action (increases compliance)
 fexofenadine (Allegra), loratadine (Claritin),
 cetirizine (Zyrtec)
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Gather data about the condition or allergic reaction that
required treatment; also assess for drug allergies
Contraindicated in the presence of acute asthma attacks
and lower respiratory diseases, such as pneumonia
Use with caution in increased intraocular pressure,
cardiac or renal disease, hypertension, asthma, COPD,
peptic ulcer disease, BPH, or pregnancy
Monitor for intended therapeutic effects
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Report excessive sedation, confusion, or hypotension
Avoid driving or operating heavy machinery, alcohol or
other CNS depressants
Do not take these medications with other prescribed or
OTC medications without checking with physician
Best tolerated when taken with meals—reduces GI upset
If dry mouth occurs, teach patient to perform frequent
mouth care, chew gum, or suck on hard candy
(preferably sugarless) to ease discomfort
 Nasal
Congestion
• Excessive nasal secretions
• Inflamed and swollen nasal mucosa
• Primary causes
 Allergies
 Upper respiratory infections (common cold)
Three main types are used

Adrenergics
• Largest group
• Sympathomimetics

Anticholinergics
• Less commonly used
• Parasympatholytics

Corticosteroids
• Topical, intranasal steroids

Two dosage forms
• Oral
• Inhaled/topically applied to the nasal membranes
 Prolonged
decongestant effects, but
delayed onset
 Effect
 No
less potent than topical
rebound congestion!!!
 Exclusively
adrenergics
 Example: pseudoephedrine
(Sudafed)
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Topical adrenergics
• Prompt onset
• Potent
• Sustained use over several days causes rebound
congestion, making the condition worse
Adrenergics
• phenylephrine (Neo-Synephrine)
Intranasal steroids
• beclomethasone dipropionate (Vancenase)
• flunisolide (Nasalide)
• fluticasone (Flonase)
Site of action: blood vessels surrounding nasal sinuses


Adrenergics
• Constrict small blood vessels that supply
URI structures
 tissues shrink, and nasal secretions in the swollen mucous
membranes are better able to drain
 Nasal stuffiness is relieved
Nasal steroids
• Anti-inflammatory effect
• Work to turn off the immune system cells involved in the
inflammatory response
• Decreased inflammation results in decreased congestion
 Nasal stuffiness is relieved
Drug Effects


Shrink engorged nasal mucous membranes
Relieve nasal stuffiness
Indications -- Relief of nasal congestion associated with:

Acute or chronic rhinitis

Common cold

Sinusitis

Hay fever

Other allergies

Reduce swelling of the nasal passage and facilitate visualization of the
nasal/pharyngeal membranes -- surgery or diagnostic procedures
Adrenergics
Steroids
Nervousness
Local mucosal dryness
Insomnia
and irritation
Palpitations
Tremors
(systemic effects due to
adrenergic stimulation of the
heart, blood vessels, and CNS)

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Decongestants may cause hypertension, palpitations, and
CNS stimulation—avoid in patients with these conditions
Patients on medication therapy for hypertension should
check with their physician before taking OTC
decongestants

Assess for drug allergies

Avoid caffeine and caffeine-containing products
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Report a fever, cough lasting longer than a week

Monitor for intended therapeutic effects
Cough Physiology
Respiratory
secretions and foreign objects are naturally removed
by the:
• Cough reflex
 Induces coughing and expectoration
 Initiated by irritation of sensory receptors in the respiratory
tract
Types of Cough


Productive cough
• Congested, removes excessive secretions
Nonproductive cough
• Dry cough
Most of the time, coughing is beneficial
 Removes excessive secretions
 Removes potentially harmful foreign substances
In some situations, coughing can be harmful, such as after hernia
repair surgery
Antitussives - Drugs used to stop or reduce coughing

Opioid and nonopioid
• Used only for nonproductive coughs!
• May be used in cases where coughing is harmful
Opioids

Suppress the cough reflex by direct action on the cough center in the
medulla
Examples:
• codeine (Robitussin A-C, Dimetane-DC)
• Hydrocodone
Nonopioids

Suppress the cough reflex by numbing the stretch receptors in the
respiratory tract and preventing the cough reflex from being stimulated
Examples:
• benzonatate (Tessalon Perles)
• dextromethorphan (Vicks Formula 44, Robitussin-DM)
benzonatate
 Dizziness, headache, sedation, nausea, and
others
dextromethorphan
 Dizziness, drowsiness, nausea
Opioids
 Sedation, nausea, vomiting, lightheadedness,
constipation
 Perform
 Assess
respiratory and cough assessment
for allergies
 Antitussive
drugs are for nonproductive
coughs
 Monitor
for intended therapeutic effects
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Report :
• Cough that lasts more than a week
• A persistent headache
• Fever
• Rash
Avoid driving or operating heavy equipment due to
possible sedation, drowsiness, or dizziness
Patients taking chewable tablets or lozenges should
not drink liquids for 30 to 35 minutes afterward
 Drugs
that aid in the expectoration
(removal) of mucus
 Reduce
the viscosity of secretions
 Disintegrate
and thin secretions

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Direct stimulation
• Directly stimulate secretory glands to increase fluid secretion
• Examples: iodine-containing products such as iodinated glycerol
and potassium iodide (less commonly used)
Reflex stimulation
• Drug causes irritation of the GI tract
• Loosening and thinning of respiratory tract secretions occur in
response to this irritation
 Example: guaifenesin
Final result:
• thinner mucus that is easier to remove
• By loosening and thinning sputum and bronchial secretions, the
tendency to cough is indirectly diminished
Used for the relief of productive coughs
associated with:
Common cold
 Bronchitis
 Laryngitis
 Pharyngitis
 Coughs caused by chronic paranasal sinusitis

guaifenesin
• Nausea, vomiting, gastric irritation
iodinated glycerol
• GI irritation, rash, enlarged thyroid gland
potassium iodide
• Iodism, nausea, vomiting, taste perversion
 Expectorants
should be used with caution in the
elderly or those with asthma or respiratory
insufficiency
 Increase
oral fluids, if permitted, to help loosen and
liquefy secretions
 Report
a fever, cough lasting longer than a week
 Monitor
for intended therapeutic effects
1. Decongestants fall into three separate groups of nasal drugs. What are they?
2. An example of an H1 antagonist used as an antihistamine is ____________.
3. List three adverse effects of H1 antagonist antihistamines.
4. Guaifenesin (Robitussin) is used as a(n) __________________, and
dextromethorphan is a(n) ________________________.
5. Patients taking antitussives should report any of the following symptoms to
their physician: _________________________________________________.
6. Name two advantages of peripherally acting antihistamines, such as
loratadine or cetirizine.
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Three separate groups of nasal decongestants are adrenergics, anticholinergics, and
topical corticosteroids.
Examples of an H1 antagonist used as an antihistamine are: diphenhydramine,
chlorpheniramine, and fexofenadine.
Adverse effects of H1 antagonist antihistamines include sedation, constipation, dizziness,
nervousness, seizures, anorexia, nausea, vertigo, visual disturbances, tinnitus, anemia,
hepatitis, insomnia, and restlessness.
Guaifenesin (Robitussin) is used as an expectorant, and dextromethorphan is a nonopioid
antitussive.
Patients taking antitussives should report any of the following symptoms to their physician:
a cough that lasts longer than a week, a persistent headache, fever, change in sputum from
clear to colored, difficult or noisy breathing, activity intolerance, and weakness.
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Two advantages of peripherally acting antihistamines: they are non-sedating, and once-aday dosing increases compliance.
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A 22-year-old college student has suffered with allergy symptoms
since moving into his dormitory. When he calls the student health
center, he is told to try an over-the-counter nasal decongestant. He
tries this and is excited about the relief he experiences until 2
weeks later, when his symptoms return. He calls the student health
center again, upset because his symptoms are now worse.
1. What explanation do you have for the worsening symptoms?
2. What patient education should he have received about this type
of drug?
3. What other over-the-counter drugs and nonpharmacologic
measures could be suggested for this situation?
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1. He is experiencing rebound congestion, which is the result of
abnormal swelling and enlargement of the nasal mucous membranes. As
a result, the nasal airway is blocked, and is relieved when more
decongestants are used. This swelling occurs after the decongestant
wears off, and is common after long-term use of topically applied
decongestants.
2. He should have been instructed that nasal decongestants should be
used for just a few days, then stopped, in order to prevent the problem
of rebound congestion. In addition, he should have been instructed on
how to use the nasal spray correctly.
3. Over-the-counter antihistamines may also be used for allergy
symptoms. Because he is in college, he may want to use the newer nonsedating antihistamines. In addition, he should reduce known allergens
in his dorm room (e.g., cigarette smoke, dust, mildew, etc.).