Lecture 26: antihistamines Flashcards by Brooke Thornburg

H1 antagonists referred to as

antihistamines

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H2 antagonists referred to as

acid blockers

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H1 antagonists

-competitive
-inverse agonists

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1st gen antihistamines

-alkylamines
-ethanolamines
-ethylenediamines
-phenothiazines
-piperadines
-piperazines

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structures

slide 26

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H1 Antagonist effects

-sedation
-anticholinergic effects (piss less, dry mouth)
-local anesthetic
-anti-serotonin
-extrapyramidal

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Sedation (H1 antagonist)

-CNS effect
-block H1/H2 receptors in wakefullness-promoting circuits
-dif from sedatives/hypnotics

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H1 Antagonist interactions

-alcohol
-anxiolytics
-antipsychotics

-drowsiness

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most sedating H1 antagonists

-ethanolamines (diphenhydramine)
-phenothiazines (promethazine)

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Anti-cholinergic mech of H1 antagonists

-anti-muscarinic (atropine-like)
-more lipid soluble = inc CNS access

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H1 antagonist anticholinergic effects

-anti-motion sickness
-anti-emetic
-dec urination
-dry mouth

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best H1 antagonist for motion sickeness/nausea

-promethazine
-dyphenhydramine
-only 1st generation drugs

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Local anesthetic H1 Antagonists

-pyrilamine
-promethazine

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anti-serotonin H1 antagonists

-cyproheptadine
-azatidine

-for headaches

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a-adrenergic antagonism H1 antagonists

-phenothiazines

-hypOtension

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extrapyramidal H1 antagonists

-phenothiazine
-promethazine

-dystonia,akathisia

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1st generation antihistamines (H1 antagonists)

-brompheniramine
-cyproheptadine
-diphenhydramine
-promethazine
-hydroxyzine
-pyrilamine

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2nd gen antihistamines (H1 antagonists)

-loratidine
-desloratadine
-fexofenadine (metabolized to terfenidine)
-cetrizine (metabolized to hydroxyzine)
-levocetirizine

2nd gen antihistamines (H1 antagonists) traits

-dec lipid solubility
-efflux from CNS by P-glycoprotein transporter
-structures slide 31

2nd gen antihistamine differences from 1st gen

-no sedation
-no antimuscarinic act
-no motion sickness/anti-emetic effect

2nd gen antihistamine mech

-block H1
-may block LTC4, neutrophil migration, eosinophil infiltration

Allergic rhinorrhea

-histamine indirectly stimulates mucus discharge via H1 on nerve endings

common cold rhinorrhea

-virus stimulates reflex independent of peripheral H1 receptors
-use 1st gen
-2nd prob not as effective

1st gen drug effect on common cold rhinorrhea

-act in brain to inhibit rhinorrhea and sneeze
-dont use 2nd gen they prob wont b effective

Topical H1 antagonists

-olopatadine (eye drops/nasal spray) -azelastine* -ketotifen* *approved for systemic use in europe

Topical H1 antagonist effects

-indicated for treatment of seasonal allergic rhinitis and conjunctivitis -all cause drowsiness if taken orally or as nasal spray

clinical use of H1 antagonists

-seasonal and perennial allergic rhinoconjunctivitis -chronic urticaria -motion sickeness (diphenhydramine, meclizine, promethazine) -w epinephrine for anaphylaxis (diphenhydramine give parenterally)

Adverse effects of H1 receptor ANTAgonists

-sedation and interactions w other sedatives (1st gen only) -anti-cholinergic effects

1st gen drugs contraindicted in: (bc of anticholinergic effects)

-urinary retention -narrow angle glaucoma

how do sedative effects of antihistamines differ from sedatives/hypnotics?

-CNS stimulation at high dose -paradoxical excitation in kids

most sedative antihistamines

-ethanolamines and phenothiazines -ex: diphenhydramine and promethazine

Effect of 2nd gen antihistamines on CNS

-no sedation -none to limited CNS affects

OTC sleep aids

-sominex and nytol -contain diphenhydramine

Antihistamine patient information

-report history of glaucoma, urinary retention, pregnancy -drowsiness/dizziness -avoid alcohol and other CNS depressants -report any involuntary movements w phenothiazines

H2 antagonists

-famotidine -cimetidine -nizatidine -ranitidine

H2 antagonist use

-reduce gastric acid secretion -peptic ulcer -gerd

H2 antagonist side effects

-CNS dysfunction -antiandrogen (gynecomastia, galactorrhea) -impotence -blood dyscrasias -hepatotoxicity

GCs used in allergic rhinitis

-fluticasone -budesonide -mometasone

GCs for allergic rhinitis characteristics

-nasal sprays -slow onset (may take days) -may suppress HPA axis w high doses

Fluticasone absorption

-low absorption

budesonide absorption

1/3 dose absorbed in less than hour

Role of T cells in allergic rhinitis

-chemoattractant -eosinophils/neutrophils/basophils -inflammation

GC effect on TH2 cells

-decrease cytokine expression