Antihistamines

Chapter 69

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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.– 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

Drugs for Treating Allergic Rhinitis, Coughs, Colds

Ch 75

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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– 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

Treatment of Coughs

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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

• Decongestants• Antitussives• Analgesics• Antihistamines - anticholinergic to suppress mucus• Caffeine

Treatment of Severe Allergy

Chapter 17

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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?) (Throw it

away!)

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• TEs (Therapeutic Effects)– Vasoconstriction (most common use)

• 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 tissuesThe 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

Selected Drugs for Peptic Ulcer Disease (PUD)

Chapter 76

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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

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• DD, DF

– 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

• DD – may interfere with absorption of other drugs