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Antihistamines
Chapter 69
Outcomes
• Identify concepts related to medication classifications
and application to manage allergic reactions,
conditions of the upper respiratory system, acid
indigestion and gastric reflux.
• Choose nursing interventions related to the applied
pharmacokinetics and pharmacodyanmics specific to
these medications
• Implement the nursing process in the administration
of medication classes covered herein
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Background
• Histamines – (Predominantly H1)
– Endogenous
– Vessel effects
– Bronchi effects
– Stomach effects
• Secretes Mucus
– Greatest interest
• Allergic reactions (mild / anaphylaxis)
• PUD (Peptic Ulcer Disease)
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Histamine Release
• Allergic response
– Requires IgE antibodies
– Prior exposure to allergen
• Non-allergic – direct stimulation of cells
– Some drugs, chemicals, radiocontrast media,
plasma expanders - require no prior exposure
– Cell injury (histamines can cause)
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Physio / Pharm Effects
• H1 Stimulation
– Vasodilation (If this, then?) BP drops, nose gets stuffy,
edema, puffy eyes, etc.
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–
–
–
–
Vessel wall cells contract (If this, then?)
Bronchoconstriction (If this, then?) Trouble breathing
Itching & pain
Mucus secretion
CNS effect – cognition / memory / sleep
• H2 Stimulation
– Secretion of gastric acid (If this, then?)
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Allergies & Pharmacology
• Mild Allergy
– Hay fever, urticaria, mild transfusion rx.
– Sxms caused by? histamines
– TX?
• Severe
– Anaphylactic shock (bronchocontriction,
hypotension, & edema of glottis)
– Sxms caused by? leukotrienes
– TX? (ch 17) Epi
• Other Uses
– Common cold – runny nose
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Antihistamines: 1st Generation
• H1 Antagonists (classic antihistamines)
– No single prototype
• dyphenhydramine [Benadryl]
– Highly sedating
• MOA
– Blockers (1st Gen)
• Selectively bind to histaminic receptors
• Can also bind to nonhistaminic receptor
(muscarinic)
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• Therapeutic Effects (TE)
– Vessels (If blocks histamine, then ?)
– Capillaries (If blocks, then ?)
– Sensory nerves (If, then) – itching relief
– Mucous membranes (If, then)
– CNS
• Therapeutic doses (If, then) - sedation
• Overdose – stimulation, seizures – esp. in young
– Other: relieve N & V, motion sickness
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• Clinical uses
– Mild allergies, seasonal rhinitis, acute
urticaria, allergic conjunctivitis, mild
transfusion reactions
– Some block muscarinic & H1 receptor sites –
useful for motion sickness
• promethazine [Phenergan] and dimenhydrinate
[Dramamine]
– Insomnia (diphenhydramine [Benadryl])
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• Adverse Effects
– CNS
• Sedation = to excess ETOH (If this, then?)
• Dizziness, lack of coordination, confusion
• Paradoxical: insomnia, excitation, tremors,
convulsions
– GI
• N, V, Diarrhea / constipation, loss of appetite
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– Anticholinergic effects
• Dry mouth, throat, nasal passages, thickened secretions,
(cautions?) urinary hesitancy, constipation, palpitations
– Cardiac Dysrhythmias w some 2nd Gen.
• Torsades de pointes, V-fib
• terfenadine [Seldane] & astemizole [Hismanal]
• Contraindications – third trimester
• Precautions: asthma, children/elderly, urinary
retention, HTN, OA glaucoma, prostatic
hypertrophy
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• DD
– ETOH, barbs/benzos/ opioids, antidepressants
• Toxicity
– Sxms similar to atropine poisoning (anticholinergic),
hyperpyrexia (super fever, can kill children)
– Can lead to death in children via excitation,
hallucinations, convulsion, coma, CV collapse, death.
– Tx: remove and support – may use charcoal followed
with cathartics
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Antihistamines: 2nd Generation
• Prototypes - Fexofenadine [Allegra] EXPENSIVE
• MOA / TE – antagonists of histamine to
relieve sxms of allergic rhinitis and
urticarias
• ADME - Do not readily cross B-B barrier
therefore non-sedating w minimized
anticholinergic SEs
• Precautions – ETOH, drowsiness, liver,
kidneys
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Drugs for Treating Allergic
Rhinitis, Coughs, Colds
Ch 75
Allergic Rhinitis
• Review of sxms
• Commonly associated disorders
• Seasonal vs. Perennial
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Antihistamines
•
•
•
•
First line - oral
Prophylaxis first
No use against cold
Adverse effects
– 1st gen - sedation, anticholinergic
– 2nd gen - rare
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Intranasal Glucocorticoids
• Prototype: fluticasone (Flonase)
• Action / Use
– Predominantly local anti-inflammatory
– First line - Most effective against all sxms
• Adverse Effects
– Drying, burning, or itching (when applied topically)
– Rare - sore throat, epistaxis and HA
– Rare - systemic – adrenal suppression / slowed
growth in children
• Dose: Adults – 2 sprays of 50 mcg. once daily
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Intranasal Cromolyn
• Prototype: cromolyn (NasalCrom)
• Action / Use
– Suppresses release of histamine
– Best suited for prophylaxis
– May not see results for week or more
• Adverse effects
– Negligible
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Sympathomimetics (fight or flight)
(Decongestants)
• Prototype: phenylephrine (Neo-Synephrine)
• Action / Uses - Reduce nasal congestion via ?
– Topical - rapid and intense
– Oral - prolonged, moderate, systemic effects
– Also used in sinusitis and colds
• Adverse effects
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–
–
–
–
Rebound congestion
CNS stimulation
Cardiovascular
Hemorrhagic stroke w phenylporpanolamine
Abuse (pseudoephedrine and ephedrine)
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Sympathamometics (cont’d)
• Nasal sprays
– 2 – 3 sprays every 4 hours needed – not to
exceed 5 consecutive days (to reduce
dependence)
– What cocaine is
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Anticholinergics
• Prototype: ipratropium bromide (Atrovent)
• Action / Use
– Blocks cholinergic receptors and inhibits
secretions to relieve rhinorrea in allergic
rhinitis and asthma
– No systemic effects
• SEs: drying, irritation
– Dry mouth, throat, etc.
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Leukotriene Antagonist
• Prototype: montelukast (Singulair)
• Action / Uses;
– Blocks binding of leukotrienes to receptors
thereby relieving nasal congestion
• Leukotrienes normally vasodilate and increase
vascular permeability, causing congestion
• Adverse Effects: None significant
– Table 75-1 in book
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Treatment of Coughs
Antitussives
• Antitussives (cough suppressants)
– Actions / use: elevate cough threshold in
common cold and URTI
• Opioid (codeine and hydrocodone) – best (stops
cough in the brain)
– Dosage: codeine 10 to 20 mg up to 6 times daily
• Nonopioid (dextromethorphan) - best
– Opioid derivative w/o euphoria or dependence
– Can lead to mind-body dissociation equal to PCP
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Expectorants
• Prototype - guaifenesin (Mucinex)
• MOA / Use – increases flow of respiratory tract
secretions
• Don’t use for COPD or something else… read
the friggin book
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Mucolytics
• Prototype – acetylcysteine (Mucomyst)
– Can also use hypertonic saline
• MOA / Use – directly thins secretions
• ADME
– Inhalation delivery
• Adverse effects
– Can trigger bronchospasm
– Antidote for tylenol!
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Colds
• Drug regimen
– Symptomatic
– Combination products
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•
•
•
•
Decongestants
Antitussives
Analgesics
Antihistamines - anticholinergic to suppress mucus
Caffeine
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Treatment of Severe Allergy
Chapter 17
Adrenergic Agonist
• Prototype - epinephrine
• MOA/Use
– Direct receptor binding ( 1&2, 1&2) mimicing the
sympathetic nervous system
• Also known as sympathomimetic & catecholamine (think of
these to mean stimulation)
• ADME
– Broken down quickly in stomach & significant 1st pass
effect (can’t take it PO)
– Can’t cross blood-brain
– Discolors (pink/brownish) as it degrades (If, then?)
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(Throw it away!)
• TEs (Therapeutic Effects)
– Vasoconstriction (most common use)
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•
•
•
•
Hemostasis
Augments local anesthetic via vascontriction
Elevates blood pressure
Restores beating heart
Bronchodilates
– TOC for anaphylactic shock
– Mydriasis (rare use)
• Adverse effects:
– HTN, necrosis, bradycardia w HTN, tachycardia,
tremor, chest pain, elevated blood sugar
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Table 17-3
• DD
– MAOIs
– TCAs
– General anesthestics (myocardial effects)
• Precautions
– IV admin can cause potentially fatal effect –
check concentrations!
– Insure patent and healthy IV site (you don’t
want epi going into the tissues
The range can be from 1:100,000 to 1:1,000… make sure to read the
label!!!!
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EpiPen
• Anaphylactic deaths
– PCN, venoms & foods
• Device: EpiPen & EpiPen Jr.
• Storage & Replacement
– Room temp – dark – do NOT refrigerate
• Injection
• Duration 10-20 mins
• SEs
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Selected Drugs for
Peptic Ulcer Disease (PUD)
Chapter 76
Histamine2-Receptor Antagonists
• Prototype: cimetadine (Tagamet)
– First choice for gastric / duodenal ulcers
– Action / Uses:
• Promote healing through acid reduction
• GERD, Aspiration Pneumonitis (aspiration of acid in the lungs) in
obese & gyne prior to anesthesia
• Adverse effects
– Low incidence of gynecomastia (breasts devlpmnt in men),
reduced libido, impotence, CNS depression / excitement,
pneumonia
• DD
– Inhibits hepatic drug metabolism – therefore?
– Major Drugs of concern – warfarin, phenytoin, theophylline,
lidocaine
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Famotidine (Pepsid)
• For Heartburn, acid indigestion, sour
stomach
• Cut dose in renal compromise/failure
• No antiandrogenic effects
• No effect on hepatic metabolism of other
drugs
– Doesn’t cause a lot of the things that Tagamet
does
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Proton Pump Inhibitors
• Prototype - omeprazole (Prilosec)
• Action / Uses – suppress secretion of gastric acid
– Irreversible - days - up to weeks after cessation
– Superior to H2RAs
• Adverse effects
– HA, diarrhea, N & V
– Long term may increase risk of CA
• ADME – give 30 min before meal – once daily
• DD, DF
– Reduced absorption of atazanavir, ketocanazole and
itracanazole – NOT recommended concurrently with atazanavir
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Antacids
• Prototypes - magnesium hydroxide / aluminum
hydroxide
• Action / Uses – alkaline agents that neutralize
acid & decrease destruction of gut wall
– And prophylactically to prevent aspiration pneumonia
• ADME
– Take regularly to promote healing
– In PUD: 1 and 3 hr after each meal & at bedtime
– Goal is gastric pH greater than 5
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• Adverse effects
– Constipation (aluminum base) / Diarrhea
(magnesium base)
– Sodium “loading”
– High levels in renal failure clients
• DD – may interfere with absorption of
other drugs
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