Antihistamines

1. DRUGS AFFECTING THE
RESPIRATORY SYSTEM
Topics Lilley
Respiratory 35 & 36
Anti TB 40

2. Respiratory System Drugs
Antihistamines, Decongestants,
Antitussives, and Expectorants

3. Respiratory System Drugs
Common Cold
 Viral infection
 (rhinovirus or influenza virus)
 Virus invades(mucosa) of upper respiratory tract
 Inflammatory response
 Virus invades(mucosa) of upper respiratory tract

4. Respiratory System Drugs
Cold - Inflammatory Response
 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

5. Respiratory System Drugs
Treatment of the Common Cold
 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

6. Respiratory System Drugs
Antihistamines
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

7. Respiratory System Drugs
Antihistamines
 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)

8. Respiratory System Drugs
Antihistamines
 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

9. Respiratory System Drugs
Antihistamines
 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

10. Respiratory System Drugs
Histamine vs. Antihistamine
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

11. Respiratory System Drugs
Histamine vs. Antihistamine
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)

12. Respiratory System Drugs
Antihistamines: Indications
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

13. Respiratory System Drugs
Symptoms of anticholinergic delirium
include hot, dry skin; dry mucous membranes;
dilated pupils; absent bowel sounds; and
tachycardia. Physicians must first determine and
remove the offending agent because patients
are at a high risk for cholinergic crisis.

14. Respiratory System Drugs
Antihistamines: Adverse Effects
 Anticholinergic (drying) effects, most
common
 Dry mouth
 Difficulty urinating
 Constipation
 Changes in vision
 Drowsiness
 Mild drowsiness to deep sleep

15. Respiratory System Drugs
Two Types of Antihistamines
 Traditional
 Older
 Work both peripherally and centrally
 Have anticholinergic effects, making them more effective than non-sedating
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)

16. Respiratory System Drugs
Antihistamines – Nsg Implications
 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

17. Respiratory System Drugs
Antihistamines – Pt Education
 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

18. Respiratory System Drugs
Decongestants
 Nasal Congestion
 Excessive nasal secretions
 Inflamed and swollen nasal mucosa
 Primary causes
 Allergies
 Upper respiratory infections (common cold)

19. Respiratory System Drugs
Decongestants
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

20. Respiratory System Drugs
Oral Decongestants
 Prolonged decongestant effects, but delayed
onset
 Effect less potent than topical
 No rebound congestion!!!
 Exclusively adrenergics
 Example: pseudoephedrine (Sudafed)

21. Respiratory System Drugs
Topical Nasal Decongestants
 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)

22. Respiratory System Drugs
Mechanism of Action
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

23. Respiratory System Drugs
Decongestants
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

24. Respiratory System Drugs
Adverse Effects
Adrenergics Steroids
Nervousness Local mucosal dryness
Insomnia and irritation
Palpitations
Tremors
(systemic effects due to
adrenergic stimulation of the
heart, blood vessels, and CNS)

25. Respiratory System Drugs
Nursing Implications
 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
 Report a fever, cough lasting longer than a week

26. Respiratory System Drugs
Antitussives
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

27. Respiratory System Drugs
Antitussives
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

28. Respiratory System Drugs
Mechanism of Action
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)

29. Respiratory System Drugs
Antitussives: Adverse Effects
benzonatate
 Dizziness, headache, sedation, nausea, and
others
dextromethorphan
 Dizziness, drowsiness, nausea
Opioids
 Sedation, nausea, vomiting, lightheadedness,
constipation

30. Respiratory System Drugs
Nursing Implications
 Perform respiratory and cough assessment
 Assess for allergies
 Antitussive drugs are for nonproductive coughs
 Monitor for intended therapeutic effects

31. Respiratory System Drugs
Patient Education
 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

32. Respiratory System Drugs
Expectorants
 Drugs that aid in the expectoration
(removal) of mucus
 Reduce the viscosity of secretions
 Disintegrate and thin secretions

33. Respiratory System Drugs
Mechanism of Action
 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

34. Respiratory System Drugs
Indications
Used for the relief of productive coughs
associated with:
 Common cold
 Bronchitis
 Laryngitis
 Pharyngitis
 Coughs caused by chronic paranasal sinusitis

35. Respiratory System Drugs
Common Adverse Reactions
guaifenesin
 Nausea, vomiting, gastric irritation
iodinated glycerol
 GI irritation, rash, enlarged thyroid gland
potassium iodide
 Iodism, nausea, vomiting, taste perversion

36. Respiratory System Drugs
Nursing Implications & Pt Ed
 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

37. Review
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.

38. Review Answers
 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-a-day

39. Review – Case Study
 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?

40. Case Study Answers
 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 non-
sedating antihistamines. In addition, he should reduce known allergens in
his dorm room (e.g., cigarette smoke, dust, mildew, etc.).