E2: Antihistamines Flashcards
Histamine can cause: (2 conditions)
Immediate hypersensitivity
Allergic rxns
Name 3 situations that can cause histamine release
Allergic Response (IgE and Ag)
Drugs
Venoms
What 3 drugs can induce a histamine release?
Morphine
Codeine
Radiocontrast dyes
List 3 physiologic effects of an H1 receptor.
Allergic response
Vasodilation (stimulates endothelium to release NO)
Bronchospasm (problem in ashthmatics!)
What are the 3 components of the Lewis Triple Response?
Flush
Flare
Wheals
List 3 skin effects caused by the H1 receptor
Itch
Hives
Edema
(Caused by increased capillary permeability and separation of endothelial cells)
List 2 physiologic effects of the H2 receptor.
Gastric acid secretion
Vasodilation (at higher concentrations)
When H1/H2 receptors cause vasodilation, what is the body’s physiologic response?
Decreased blood pressure
Reflex tachycardia
Describe the H3 receptor
Presynaptic in brain
Responsible for sleep
INHIBITS RELEASE OF HISTAMINE
Describe the H4 receptor
Stimulates chemotaxis in inflammation and allergic rxn
Large doses of histamine may result in:
SHOCK!
Name the 1st gen H1 Antagonists (3)
Diphenhydramine (Benadryl)
Dimenhydrinate (Dramamine)
Promethazine (Phenergan)
How do 1st gen H1 Antagonists work? How can histamine overcome this?
Compete directly with histamine
-Effect is dependent on concentration of drug (too much histamine can override the medication effect)
What are 1st gen H1 Antagonists used for clinically (4)?
Motion sickness *use prophylactically!
Sedation
Dry up secretions
Anti-emetic (Promethazine)
What are 3 adverse effects of 1st gen H1 Antagonists?
Sedation (AVOID OTHER CNS DEPRESSANTS!)
Dry mouth
Decreased seizure threshold
What population is contraindicated for use of a 1st gen H1 Antagonist?
Children 4 yo or younger
What are the 2nd gen H1 Antagonists?
Loratadine (Claritin)
Certirizine (Zyrtec)
Fexofenadine (Allegra)
How do the 2nd gen H1 antagonists differ from the 1st gen?
Non-sedating (little to no CNS penetration)
No anticholinergic effect
What are 3 clinical uses of 2nd gen H1 Antagonists? (3)
Allergic rhinitis
Conjunctivitis (topical?)
Itching/hives (topical?)
What is the administration of 2nd gen H1 Antagonists and how often are they typically taken?
Oral
1x per day
2nd gen H1 Antagonists are metabolized by:
CYP-450
What 4 drugs should be avoided with 2nd gen H1 Antagonists?
Erythromycin
Ketoconazole
Cimetidine
Grapefruit juice (Effects heart)
What 2nd gen H1 Antagonist is eliminated exclusively by the kidney (therefore great option for pt with liver dz)?
Certirizine (Zyrtec)
Name the Nasal H1 Antagonist
Azelastine
Name the Histamine Release Inhibitors
Cromolyn
Azelastine
Ceterizine (Zyrtec)
What are the general adverse effects of H1 antagonists?
GI upset (take with food)
TERATOGENIC!
Allergic rxn with topical applications
Describe the primary sxs associated with acute poisoning of 1st and 2nd gen H1 Antagonists.
1st gen: Just like atropine poisoning
2nd gen: Cardiac arrhythmias
*Overdose usually only happens in kids
