antihistamines

Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.
Antihistamines,Antihistamines,
Decongestants,Decongestants,
Antitussives,Antitussives,
andand
ExpectorantsExpectorants
Drugs Affecting theDrugs Affecting the
Respiratory SystemRespiratory System

Understanding the Common ColdUnderstanding the Common Cold
• Most caused by viral infectionMost caused by viral infection
(rhinovirus or influenza virus—the “flu”)(rhinovirus or influenza virus—the “flu”)

• Virus invades tissues (mucosa) of upperVirus invades tissues (mucosa) of upper
respiratory tract, causing upper respiratoryrespiratory tract, causing upper respiratory
infection (URI).infection (URI).
• Excessive mucus production results from theExcessive mucus production results from the
inflammatory response to this invasion.inflammatory response to this invasion.
• Fluid drips down the pharynx into theFluid drips down the pharynx into the
esophagus and lower respiratory tract,esophagus and lower respiratory tract,
causing cold symptoms: sore throat,causing cold symptoms: sore throat,
coughing, upset stomach.coughing, upset stomach.

• Irritation of nasal mucosa often triggers theIrritation of nasal mucosa often triggers the
sneeze reflex.sneeze reflex.
• Mucosal irritation also causes release ofMucosal irritation also causes release of
several inflammatory and vasoactiveseveral inflammatory and vasoactive
substances, dilating small blood vessels insubstances, dilating small blood vessels in
the nasal sinuses and causing nasalthe nasal sinuses and causing nasal
congestion.congestion.

Treatment of the Common ColdTreatment of the Common Cold
• Involves combined use of antihistamines,Involves combined use of antihistamines,
nasal decongestants, antitussives, andnasal decongestants, antitussives, and
expectorants.expectorants.
• Treatment is SYMPTOMATIC only, notTreatment is SYMPTOMATIC only, not
curative.curative.
• Symptomatic treatment does not eliminateSymptomatic treatment does not eliminate
the causative pathogen.the causative pathogen.

Instructors may want to useInstructors may want to use
EIC Image #83:EIC Image #83:
Upper Respiratory TractUpper Respiratory Tract

Treatment of the Common ColdTreatment of the Common Cold
• Difficult to identify whether cause is viral orDifficult to identify whether cause is viral or
bacterial.bacterial.
• Treatment is “empiric therapy,” treating theTreatment is “empiric therapy,” treating the
most likely cause.most likely cause.
• Antivirals and antibiotics may be used, butAntivirals and antibiotics may be used, but
viral or bacterial cause may not be easilyviral or bacterial cause may not be easily
identified.identified.

AntihistaminesAntihistamines
Drugs that directly compete with histamineDrugs that directly compete with histamine
for specific receptor sites.for specific receptor sites.
• Two histamine receptors:Two histamine receptors:
– HH11 histamine-1histamine-1
– HH22 histamine-2histamine-2

HH22 Blockers or HBlockers or H22 AntagonistsAntagonists
– Used to reduce gastric acid in PUDUsed to reduce gastric acid in PUD
– Examples:Examples: cimetidine (Tagamet),cimetidine (Tagamet),
ranitidine (Zantac), orranitidine (Zantac), or
famotidine (Pepcid)famotidine (Pepcid)

HH11 antagonists are commonly referredantagonists are commonly referred
to asantihistaminesto asantihistamines
• Antihistamines have several effectsAntihistamines have several effects::
– AntihistaminicAntihistaminic
– AnticholinergicAnticholinergic
– SedativeSedative

Antihistamines: Mechanism of ActionAntihistamines: Mechanism of Action
BLOCK action of histamine at the receptor sitesBLOCK action of histamine at the receptor sites
• Compete with histamine for binding at unoccupiedCompete with histamine for binding at unoccupied
receptors.receptors.
• CANNOT push histamine off the receptor if alreadyCANNOT push histamine off the receptor if already
bound.bound.

• The binding of HThe binding of H11 blockers to the histamineblockers to the histamine
receptors prevents the adversereceptors prevents the adverse
consequences of histamine stimulation:consequences of histamine stimulation:
– VasodilationVasodilation
– Increased gastrointestinal and respiratoryIncreased gastrointestinal and respiratory
secretionssecretions
– Increased capillary permeabilityIncreased capillary permeability

• More effective in preventing the actions ofMore effective in preventing the actions of
histamine rather than reversing themhistamine rather than reversing them
• Should be given early in treatment, beforeShould be given early in treatment, before
all the histamine binds to the receptorsall the histamine binds to the receptors

Histamine vs. Antihistamine EffectsHistamine vs. Antihistamine Effects
Cardiovascular (small blood vessels)Cardiovascular (small blood vessels)
• Histamine effects:Histamine effects:
– Dilation and increased permeabilityDilation and increased permeability
(allowing substances to leak into tissues)(allowing substances to leak into tissues)
• Antihistamine effects:Antihistamine effects:
– Prevent dilation of blood vesselsPrevent dilation of blood vessels
– Prevent increased permeabilityPrevent increased permeability

Smooth Muscle (on exocrine glands)Smooth Muscle (on exocrine glands)
– Stimulate salivary, gastric, lacrimal, andStimulate salivary, gastric, lacrimal, and
bronchial secretionsbronchial secretions
• Antihistamine effects:Antihistamine effects:
– Prevent salivary, gastric, lacrimal, andPrevent salivary, gastric, lacrimal, and
bronchial secretionsbronchial secretions

Immune SystemImmune System
(Release of substances commonly(Release of substances commonly
associated with allergic reactions)associated with allergic reactions)
– Mast cells release histamine and otherMast cells release histamine and other
substances, resulting in allergic reactions.substances, resulting in allergic reactions.
• Antihistamine effect:Antihistamine effect:
– Binds to histamine receptors, thus preventingBinds to histamine receptors, thus preventing
histamine from causing a response.histamine from causing a response.

Antihistamines: Other EffectsAntihistamines: Other Effects
Skin:Skin:
• Block capillary permeability, wheal-and-flareBlock capillary permeability, wheal-and-flare
formation, itchingformation, itching
Anticholinergic:Anticholinergic:
• Drying effect that reduces nasal, salivary, andDrying effect that reduces nasal, salivary, and
lacrimal gland secretions (runny nose, tearing, andlacrimal gland secretions (runny nose, tearing, and
itching eyes)itching eyes)
Sedative:Sedative:
• Some antihistamines cause drowsinessSome antihistamines cause drowsiness

Antihistamines: Therapeutic UsesAntihistamines: Therapeutic Uses
Management of:Management of:
• Nasal allergiesNasal allergies
• Seasonal or perennial allergic rhinitisSeasonal or perennial allergic rhinitis
(hay fever)(hay fever)
• Allergic reactionsAllergic reactions
• Motion sicknessMotion sickness
• Sleep disordersSleep disorders

10 to 20% of general population is sensitive10 to 20% of general population is sensitive
to various environmental allergies.to various environmental allergies.
• Histamine-mediated disorders:Histamine-mediated disorders:
– Allergic rhinitisAllergic rhinitis
(hay fever, mold and dust allergies)(hay fever, mold and dust allergies)
– AnaphylaxisAnaphylaxis
– Angioneurotic edemaAngioneurotic edema
– Drug feversDrug fevers
– Insect bite reactionsInsect bite reactions
– Urticaria (itching)Urticaria (itching)

Antihistamines: Therapeutic UsesAntihistamines: Therapeutic Uses
Also used to relieve symptoms associatedAlso used to relieve symptoms associated
with the common cold:with the common cold:
• Sneezing, runny noseSneezing, runny nose
• Palliative treatment, not curativePalliative treatment, not curative

Antihistamines: Side effectsAntihistamines: Side effects
• Anticholinergic (drying) effects, mostAnticholinergic (drying) effects, most
common:common:
– Dry mouthDry mouth
– Difficulty urinatingDifficulty urinating
– ConstipationConstipation
– Changes in visionChanges in vision
• DrowsinessDrowsiness
– (Mild drowsiness to deep sleep)(Mild drowsiness to deep sleep)

Antihistamines: Two TypesAntihistamines: Two Types
• TraditionalTraditional
oror
• Nonsedating/Peripherally ActingNonsedating/Peripherally Acting

Antihistamines:Antihistamines:
TraditionalTraditional
• OlderOlder
• Work both peripherally and centrallyWork both peripherally and centrally
• Have anticholinergic effects, making them moreHave anticholinergic effects, making them more
effective than nonsedating agents in some caseseffective than nonsedating agents in some cases
Examples:Examples: diphenhydramine (Benadryl)diphenhydramine (Benadryl)
chlorpheniramine (Chlor-Trimeton)chlorpheniramine (Chlor-Trimeton)

Antihistamines:Antihistamines:
Nonsedating/Peripherally ActingNonsedating/Peripherally Acting
• Developed to eliminate unwanted side effects,Developed to eliminate unwanted side effects,
mainly sedationmainly sedation
• Work peripherally to block the actions of histamine;Work peripherally to block the actions of histamine;
thus, fewer CNS side effectsthus, fewer CNS side effects
• Longer duration of action (increases compliance)Longer duration of action (increases compliance)
Examples:Examples: fexofenadine (Allegra)fexofenadine (Allegra)
loratadine (Claritin)loratadine (Claritin)

Nursing Implications: AntihistaminesNursing Implications: Antihistamines
• Gather data about the condition or allergic reactionGather data about the condition or allergic reaction
that required treatment; also, assess for drugthat required treatment; also, assess for drug
allergies.allergies.
• Contraindicated in the presence of acute asthmaContraindicated in the presence of acute asthma
attacks and lower respiratory diseases.attacks and lower respiratory diseases.
• Use with caution in increased intraocular pressure,Use with caution in increased intraocular pressure,
cardiac or renal disease, hypertension, asthma,cardiac or renal disease, hypertension, asthma,
COPD, peptic ulcer disease, BPH, or pregnancy.COPD, peptic ulcer disease, BPH, or pregnancy.

• Instruct patients to report excessiveInstruct patients to report excessive
sedation, confusion, or hypotension.sedation, confusion, or hypotension.
• Avoid driving or operating heavy machinery,Avoid driving or operating heavy machinery,
and do not consume alcohol or other CNSand do not consume alcohol or other CNS
depressants.depressants.
• Do not take these medications with otherDo not take these medications with other
prescribed or OTC medications withoutprescribed or OTC medications without
checking with prescriber.checking with prescriber.

• Best tolerated when taken with meals—Best tolerated when taken with meals—
reduces GI upset.reduces GI upset.
• If dry mouth occurs, teach patient to performIf dry mouth occurs, teach patient to perform
frequent mouth care, chew gum, or suck onfrequent mouth care, chew gum, or suck on
hard candy (preferably sugarless) to easehard candy (preferably sugarless) to ease
discomfort.discomfort.
• Monitor for intended therapeutic effects.Monitor for intended therapeutic effects.

DecongestantsDecongestants

Nasal CongestionNasal Congestion
• Excessive nasal secretionsExcessive nasal secretions
• Inflamed and swollen nasal mucosaInflamed and swollen nasal mucosa
• Primary causes:Primary causes:
– AllergiesAllergies
– Upper respiratory infections (common cold)Upper respiratory infections (common cold)

Two main types are used:Two main types are used:
• Adrenergics (largest group)Adrenergics (largest group)
• CorticosteroidsCorticosteroids

Two dosage forms:Two dosage forms:
• OralOral
• Inhaled/topically applied to the nasal membranesInhaled/topically applied to the nasal membranes

Oral DecongestantsOral Decongestants
• Prolonged decongestant effects,Prolonged decongestant effects,
but delayed onsetbut delayed onset
• Effect less potent than topicalEffect less potent than topical
• No rebound congestionNo rebound congestion
• Exclusively adrenergicsExclusively adrenergics
• Examples:Examples: phenylephrinephenylephrine
pseudoephedrine (Sudafed)pseudoephedrine (Sudafed)

Topical Nasal DecongestantsTopical Nasal Decongestants
• Both adrenergics and steroidsBoth adrenergics and steroids
• Prompt onsetPrompt onset
• PotentPotent
• Sustained use over several days causesSustained use over several days causes
rebound congestion, making the conditionrebound congestion, making the condition
worseworse

Topical Nasal DecongestantsTopical Nasal Decongestants
• Adrenergics:Adrenergics:
ephedrine (Vicks)ephedrine (Vicks) naphazoline (Privine)naphazoline (Privine)
oxymetazoline (Afrin)oxymetazoline (Afrin) phenylephrinephenylephrine
(Neo Synephrine)(Neo Synephrine)
• Intranasal Steroids:Intranasal Steroids:
beclomethasone dipropionatebeclomethasone dipropionate
(Beconase, Vancenase)(Beconase, Vancenase)
flunisolide (Nasalide)flunisolide (Nasalide)

Nasal Decongestants:Nasal Decongestants:
Mechanism of ActionMechanism of Action
Site of action: blood vessels surroundingSite of action: blood vessels surrounding
nasal sinusesnasal sinuses
• AdrenergicsAdrenergics
– Constrict small blood vessels that supplyConstrict small blood vessels that supply
URI structuresURI structures
– As a result, these tissues shrink and nasalAs a result, these tissues shrink and nasal
secretions in the swollen mucous membranessecretions in the swollen mucous membranes
are better able to drainare better able to drain
– Nasal stuffiness is relievedNasal stuffiness is relieved

Mechanism of ActionMechanism of Action
Site of action: blood vessels surroundingSite of action: blood vessels surrounding
nasal sinusesnasal sinuses
• Nasal steroidsNasal steroids
– Anti-inflammatory effectAnti-inflammatory effect
– Work to turn off the immune system cellsWork to turn off the immune system cells
involved in the inflammatory responseinvolved in the inflammatory response
– Decreased inflammation results in decreasedDecreased inflammation results in decreased
congestioncongestion
– Nasal stuffiness is relievedNasal stuffiness is relieved

Nasal Decongestants: Drug EffectsNasal Decongestants: Drug Effects
• Shrink engorged nasal mucous membranesShrink engorged nasal mucous membranes
• Relieve nasal stuffinessRelieve nasal stuffiness

Therapeutic UsesTherapeutic Uses
Relief of nasal congestion associated with:Relief of nasal congestion associated with:
• Acute or chronic rhinitisAcute or chronic rhinitis
• Common coldCommon cold
• SinusitisSinusitis
• Hay feverHay fever
• Other allergiesOther allergies
May also be used to reduce swelling of the nasal passage andMay also be used to reduce swelling of the nasal passage and
facilitate visualization of the nasal/pharyngeal membranesfacilitate visualization of the nasal/pharyngeal membranes
before surgery or diagnostic procedures.before surgery or diagnostic procedures.

Nasal Decongestants: Side EffectsNasal Decongestants: Side Effects
AdrenergicsAdrenergics SteroidsSteroids
nervousnessnervousness local mucosal drynesslocal mucosal dryness
and irritationand irritation
insomniainsomnia
palpitationspalpitations
tremorstremors
(systemic effects due to adrenergic stimulation of(systemic effects due to adrenergic stimulation of
the heart, blood vessels, and CNS)the heart, blood vessels, and CNS)

Nursing Implications:Nursing Implications:
Nasal DecongestantsNasal Decongestants
• Decongestants may cause hypertension,Decongestants may cause hypertension,
palpitations, and CNS stimulation—avoid inpalpitations, and CNS stimulation—avoid in
patients with these conditions.patients with these conditions.
• Assess for drug allergies.Assess for drug allergies.

Nursing Implications: DecongestantsNursing Implications: Decongestants
• Patients should avoid caffeine and caffeine-Patients should avoid caffeine and caffeine-
containing products.containing products.
• Report a fever, cough, or other symptomsReport a fever, cough, or other symptoms
lasting longer than a week.lasting longer than a week.

AntitussivesAntitussives

Cough PhysiologyCough Physiology
Respiratory secretions and foreign objects areRespiratory secretions and foreign objects are
naturally removed by thenaturally removed by the
• cough reflexcough reflex
– Induces coughing and expectorationInduces coughing and expectoration
– Initiated by irritation of sensory receptors in theInitiated by irritation of sensory receptors in the
respiratory tractrespiratory tract

Two Basic Types of CoughTwo Basic Types of Cough
• Productive CoughProductive Cough
– Congested, removes excessive secretionsCongested, removes excessive secretions
• Nonproductive CoughNonproductive Cough
– Dry coughDry cough

CoughingCoughing
Most of the time, coughing is beneficialMost of the time, coughing is beneficial
• Removes excessive secretionsRemoves excessive secretions
• Removes potentially harmful foreign substancesRemoves potentially harmful foreign substances
In some situations, coughing can be harmful,In some situations, coughing can be harmful,
such as after hernia repair surgerysuch as after hernia repair surgery

AntitussivesAntitussives
Drugs used to stop or reduce coughingDrugs used to stop or reduce coughing
• Opioid and nonopioidOpioid and nonopioid
(narcotic and non-narcotic)(narcotic and non-narcotic)
Used only for NONPRODUCTIVE coughs!Used only for NONPRODUCTIVE coughs!

Antitussives: Mechanism of ActionAntitussives: Mechanism of Action
OpioidOpioid
• Suppress the cough reflex by direct action on theSuppress the cough reflex by direct action on the
cough center in the medulla.cough center in the medulla.
Examples:Examples: codeine (Robitussin A-C,codeine (Robitussin A-C, Dimetane-DC)Dimetane-DC)
hydrocodonehydrocodone

Antitussives: Mechanism of ActionAntitussives: Mechanism of Action
NonopioidNonopioid
• Suppress the cough reflex by numbing the stretchSuppress the cough reflex by numbing the stretch
receptors in the respiratory tract and preventing thereceptors in the respiratory tract and preventing the
cough reflex from being stimulated.cough reflex from being stimulated.
Examples:Examples: benzonatate (Tessalon)benzonatate (Tessalon)
dextromethorphan (Vicks Formula 44,dextromethorphan (Vicks Formula 44,
Robitussin-DM)Robitussin-DM)

Antitussives: Therapeutic UsesAntitussives: Therapeutic Uses
• Used to stop the cough reflex when theUsed to stop the cough reflex when the
cough is nonproductive and/or harmfulcough is nonproductive and/or harmful

Antitussives: Side EffectsAntitussives: Side Effects
BenzonatateBenzonatate
• Dizziness, headache, sedationDizziness, headache, sedation
DextromethorphanDextromethorphan
• Dizziness, drowsiness, nauseaDizziness, drowsiness, nausea
OpioidsOpioids
• Sedation, nausea, vomiting, lightheadedness,Sedation, nausea, vomiting, lightheadedness,
constipationconstipation

Antitussive AgentsAntitussive Agents
• Perform respiratory and cough assessment,Perform respiratory and cough assessment,
and assess for allergies.and assess for allergies.
• Instruct patients to avoid driving or operatingInstruct patients to avoid driving or operating
heavy equipment due to possible sedation,heavy equipment due to possible sedation,
drowsiness, or dizziness.drowsiness, or dizziness.
• If taking chewable tablets or lozenges,If taking chewable tablets or lozenges,
do not drink liquids for 30 to 35 minutesdo not drink liquids for 30 to 35 minutes
afterward.afterward.

Antitussive AgentsAntitussive Agents
• Report any of the following symptoms to theReport any of the following symptoms to the
caregiver:caregiver:
– Cough that lasts more than a weekCough that lasts more than a week
– A persistent headacheA persistent headache
– FeverFever
– RashRash
• Antitussive agents are for NONPRODUCTIVEAntitussive agents are for NONPRODUCTIVE
coughs.coughs.

• Drugs that aid in the expectorationDrugs that aid in the expectoration
(removal) of mucus(removal) of mucus
• Reduce the viscosity of secretionsReduce the viscosity of secretions
• Disintegrate and thin secretionsDisintegrate and thin secretions

Expectorants: Mechanisms of ActionExpectorants: Mechanisms of Action
• Direct stimulationDirect stimulation
oror
• Reflex stimulationReflex stimulation
Final result: thinner mucus that is easier to removeFinal result: thinner mucus that is easier to remove

Expectorants: Mechanism of ActionExpectorants: Mechanism of Action
Direct stimulation:Direct stimulation:
• The secretory glands are stimulated directly toThe secretory glands are stimulated directly to
increase their production of respiratory tract fluids.increase their production of respiratory tract fluids.
Examples: terpin hydrate, iodine-containingExamples: terpin hydrate, iodine-containing
products such as iodinated glycerol andproducts such as iodinated glycerol and
potassium iodide (direct and indirectpotassium iodide (direct and indirect
stimulation)stimulation)

Expectorants: Mechanism of ActionExpectorants: Mechanism of Action
Reflex stimulation:Reflex stimulation:
• Agent causes irritation of the GI tract.Agent causes irritation of the GI tract.
• Loosening and thinning of respiratory tractLoosening and thinning of respiratory tract
secretions occur in response to this irritation.secretions occur in response to this irritation.
Examples: guaifenesin, syrup of ipecacExamples: guaifenesin, syrup of ipecac

Expectorants: Drug EffectsExpectorants: Drug Effects
• By loosening and thinning sputum andBy loosening and thinning sputum and
bronchial secretions, the tendency to coughbronchial secretions, the tendency to cough
is indirectly diminished.is indirectly diminished.

Expectorants: Therapeutic UsesExpectorants: Therapeutic Uses
Used for the relief of nonproductive coughsUsed for the relief of nonproductive coughs
associated with:associated with:
Common coldCommon cold PertussisPertussis
BronchitisBronchitis InfluenzaInfluenza
LaryngitisLaryngitis MeaslesMeasles
PharyngitisPharyngitis
Coughs caused by chronic paranasal sinusitisCoughs caused by chronic paranasal sinusitis

Expectorants: Common Side EffectsExpectorants: Common Side Effects
guaifenesinguaifenesin terpin hydrateterpin hydrate
Nausea, vomitingNausea, vomiting Gastric upsetGastric upset
Gastric irritationGastric irritation (Elixir has high alcohol(Elixir has high alcohol
content)content)

Nursing Implications: ExpectorantsNursing Implications: Expectorants
• Expectorants should be used with caution inExpectorants should be used with caution in
the elderly, or those with asthma orthe elderly, or those with asthma or
respiratory insufficiency.respiratory insufficiency.
• Patients taking expectorants should receivePatients taking expectorants should receive
more fluids, if permitted, to help loosen andmore fluids, if permitted, to help loosen and
liquefy secretions.liquefy secretions.
• Report a fever, cough, or other symptomsReport a fever, cough, or other symptoms
lasting longer than a week.lasting longer than a week.

antihistamines

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