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Pharm 3 > E2: Antihistamines > Flashcards

E2: Antihistamines Flashcards

1
Q

What cells are histamines found in?

A

Mast cells and basophils

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2
Q

What is histamine normally complexed to?

A

Protease, heparin, or chondroitin sulfate proteoglycans

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3
Q

How does an allergic response occur?

A
  • Antibody (IgE) generated. IgE binds to receptors on the surface of mast cells and basophils.
  • The antigen bridges IgE on the mast cells and activates protein kinases to increase IP3 and Ca. This activates Phospholipase A2, which increases platelet activating factor, leukotrienes
  • This all leads to mast cell degranulation and histamine release
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4
Q

Where is the H1 receptor found?

A
  • Smooth muscle
  • Endothelium
  • Brain
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5
Q

What does H1 receptor activation do the endothelium?

A

Activates NO and vasodilation

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6
Q

What does H1 receptor Activation do in the brain?

A

Wakefulness and appetite control

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7
Q

Where are H2 receptors found and what are the main effects of H2 receptor activation?

A
  • Heart, brain, and mast cells

- Gastric acid secretion and vasodilation

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8
Q

Where is the H3 receptor found and what does it do?

A
  • Presynaptic in the brain

- Inhibits release of NTs, including histamine. May promote sleep

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9
Q

Where are H4 receptors found and what do they do?

A
  • On leukocytes, eosinophils, and neutrophils

- may stimulate chemotaxis in inflammation and allergic reactions

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10
Q

Which histamine receptor can cause bronchospasm and can be a problem in asthmatics?

A

H1

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11
Q

What are the symptoms associated with histamine release?

A
  • Burning and itching
  • intense warmth
  • BP drops, HR increases, skin reddens
  • HA
  • BP recovers, edema, and hives
  • Colic, nausea, acid secretion
  • Bronchospasm
  • Anaphylaxis
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12
Q

What is the general mechanism of antihistamines?

A
  • Inverse agonist (Bascially antagonists)

- Decreases normal histamine activity and blocks the effects of released histamine

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13
Q

Do first generation H1 antagonist enter the Brain?

A

Yes, so they are very sedating

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14
Q

What are the 5 first generation H1 antagonists

A
  • Diphenhydramine
  • Doxylamine
  • Hydroxyzine
  • Dramamine
  • Promethazine
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15
Q

What two H1 antagonists are used for motion sickness because they also have muscarinic blockade?

A
  • Diphenhydramine
  • Dimenhydrinate (Dramamine)
  • Promethazine
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16
Q

What first generation H1 antagonists are used as an antiemetic and for motion sickness?

A

Promethazine (phenergan)

17
Q

Do 2nd generation H1 antagonists enter the brain? Do they have anticholinergic effects?

A
  • They do not enter the brain well so sedation is not common

- No anticholinergic effects so not useful for motion sickness

18
Q

How are 2nd generation H1 antagonists metabolized?

A

CYP450

19
Q

What are the 3 second generation H1 antagonists?

A
  • Cetirizine
  • Loratidine
  • Fexofenidine
20
Q

Who should second generation H1 antagonists be avoided in?

A

They are excreted directly by the kidney so avoid if kidney function is poor. Good for liver disease

21
Q

What are the uses of second generation H1 antagonists?

A
  • Allergic rhinitis (Best when used prophylactically)
  • seasonal itching
  • Itching and hives
  • Conjunctivitis
22
Q

What are the CNS side effects of 1st generation H1 antagonists?

A
  • Sedation (worse when combined with other CNS depressants)
  • decreased seizure threshold
  • dizziness, blurred vision, excitement, insomnia
23
Q

What are the drug interactions with 2nd generation H1 antagonists?

A
  • Erythromycin
  • Ketoconazole
  • Grapefruit juice
  • Cimetidine (Inhibits metabolism)
24
Q

What is the presentation of a 1st generation H1 antagonist overdose?

A
  • Similar to atropine poisoning

- sedation

25
Q

What is the presentation of a 2nd generation H1 antagonist overdose?

A
  • Cardiac arrhythmias occurred with older drugs

- sinus tachycardia with newer drugs

26
Q

What 3 drugs blocks histamine release?

A
  • Cromolyn
  • Azelastine (decreases histamine release AND blocks receptors)
  • Cetirizine
27
Q

What effects does histamine have on the cardiovascular system?

A

H1 and H2 can cause vasodilation, leading to decreased BP, reflex tachycardia, flushing of skin, warmth, and headache
-Large doses of histamine can result in shock du to decreased BP

28
Q

What is the Lewis triple response?

A

The reaction that occurs after I trader allowed injection of histamine.

  • Dilation of capillaries in immediate area resulting in flushing
  • dilation of arterioles causing redness over a wider area (flare)
  • swelling (wheal) in the area of capillary dilation
29
Q

How is anaphylaxis treated?

A

Epinephrine, steroids, and both H1 and H2 blockers

30
Q

First generation antihistamines block which 2 receptors?

A

H1 and muscarinic receptors, which is why they are sedating and cause dry mouth.
** second generations do not act on muscarinic receptors

31
Q

Do antihistamines treat bronchospasm?

A

-They decrease bronchospasm to a very small degree, but this is not useful in asthmatics as the bronchospastic is mediated more by leukotrienes

Pharm 3 (20 decks)

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