Antihistamines

Question 1

Ethylenediamines

Answer 1

• first group of clinically effective H1-antihistamines
• reversible competitive inhibitors
• includes pyrilamine

Question 2

Pyrilamine

Answer 2

• ethylenediamine
• h1 antihistamines (histamine antagonist)
• injectable antihistamine for dogs, cats, horses and ruminants (in combo with ephedrine)
• Also oral formulation to out in horse feed (also with ephedrine)

Question 3

Ethanolamines

Answer 3

• class of H1 antihistamines
• includes diphenhydramine (benadryl), dimenhydrinate (gravel, dramamine) and clementine (tavist).
• have significant anticholingergic effects and cause SEDATION(mild GI effects) (can get signif. dry mouth)

Question 4

Diphenhydramine

Answer 4

Benadryl
-ethanolamine
-H1 antihistamine
-significant anticholinergic effects (sedation)
Give benadryl if od on chlorpromazine tranquillizer to reactive ach/dopa balance.

Question 5

Dimenhydrinate

Answer 5

Gravol, dramamine

• ethanolamine
• H1 antihistamine
• anticholinergic effects (sedation)

Question 6

Clemastine

Answer 6

Tavist

• ethanolamine
• H1 antihistamine
• significant anti cholinergic effects (sedation)
• low oral bioavailabilty

Question 7

Alkylamines

Answer 7

Group of H1 antihistamines

• extremely enantiomer specific activity (involves the way it fits and positions itself in H1 receptor binding sites)
• paradoxical CNS stimulation
• includes chlorpheniramine

Question 8

Chlorpheniramine

Answer 8

Chlor-Trimeton

• alkylamine H1 antihistamine
• used in dogs and cats
• paradoxical CNS stimulation
• has antidepressant properties, by inhibiting serotonin reuptake (thus the SSRI zimelidine was developed from chlorpheniramine)

Question 9

Piperazines

Answer 9

• H1 antihistamines
• structurally related to ethylenediamines and ethanol amines
• significant anticholinergic adverse effects
• uses: motion sickness, vertigo, nausea and vomiting
• Includes Trimeprazine, Hydroxyzine and Cetirizine.

Question 10

Trimeprazine

Answer 10

Vanectyl-P

• piperazine family (H1 antihistamine)
• significant anticholinergic effects
• used for motion sickness, vertigo, nausea and vomiting
• used in DOGS
• tablet contains prednisolone (homeopathic dose)….works really well together.

Question 11

Hydroxyzine

Answer 11

Atarax

• piperazine family (H1 antihistamine)
• used in dogs, cats and horses
• signif. anticholinergic effects
• uses: vomiting, nausea, motion sickness and vertigo

Question 12

Cetirizine

Answer 12

Zyrtec

• second generation H1 antihistamine (but still piperazine family)
• significant anticholinergic effects
• vertigo, motion sickness, vomiting and nausea

Question 13

Tricyclic and tetracyclic antihistamines

Answer 13

• structurally related to the tricyclic antidepressants
• poor tolerability profile
• Includes cyproheptadine (periactin)

Question 14

Cyproheptadine

Answer 14

Periactin
-tricyclic/tetracyclic antiH
-antihistaminic and antiserotonergic agent
-acts as serotonin receptor antagonist
-blocks Ca channels
-used in cats for asthmatic bronchoconstriction. (histamine causes dilation in cat trachea so don’t use any others) (stimulates appetite)
used to tx photic head shaking in horses because of its serotonin blocking properties

Question 15

Second generation antihistamines

Answer 15

• H1 antihistamines
• more selective for peripheral H1 receptors
• reduces adverse drug rxns and still provides effective relief of allergic cans
• ex. allegra.
• not anticholinergic and can’t cross BBB thus NON DROWSY
• “day time” meds of nighttime/daytime packs (night time would be first generation)

Question 16

Third generation antihistamines

Answer 16

• active enantiomer or metabolite derivatives of second gen drugs
• have increase efficacy with fewer adverse drug rxns
• no reason to use in vet med because can make dog drowsy
• includes levocetirizine, desloratadine and fexofenadine