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Pharm II > Antihistamines > Flashcards

Antihistamines Flashcards

1
Q

What is the role of histamine in immune modulation?

A
  • Vasodilation →capillaries become permeable → allows for WBC to move into site of “threat”
    • leads to facial flushing and edema
    • separation of endothelial cells → urticaria
    • Induces fluid secretion
    • Gives rise to classic allergic symptoms
      • runny nose, watery eyes etc.
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2
Q

Morphine is a good example…..5/16

A
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3
Q

2nd gen H1 antihistamines

  • Indication?
  • Selective for?
  • BBB penetration.. yes or no?
  • Onset of action/duration of action?
  • DOC for ?
A
  • Indication?
    • allergic symptoms only
  • Selective for?
    • highly selective for H1 receptors with no other receptor effects
  • BBB penetration.. yes or no?
    • Limited BBB penetration (b/c these drugs are less lipophilic)
  • Onset of action/duration of action?
  • Rapid onset of action (1 hr); longer duration of action
  • DOC for elderly pts
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4
Q
  • Available H2 receptor anatagonist?
  • ADR’s?
  • DDI’s?
A
  • Ranitidine
  • Cimetidine
  • Nizatidine
  • Famotidine

ADR’s:

  • Most common are CNS related
    • HA, dizzy, fatigue, confusion
      • These are increased in elderly and renal impairment
  • Dose related gynecomastia occurs with cimetidine
    • b/c cimetidine is also a weak androgen

DDI’s

  • Drugs that need acid for proper absorption (b/c this is acid suppressive therapy)
    • Ketoconazole, itraconazole, protease inhibitors
  • Cimetidine inhibits most CYP450 enzyme pathways so it has a TON of DDI’s
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5
Q

2nd gen. H1 antihistamines

  • Agent available?
  • Clinical notes?
A
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6
Q

Histamine Receptors:

  • Receptor types?
    • which one has the widest distribution through out the body?
  • Location of receptors?
  • Action of receptors?
A
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7
Q
  1. Histamine is stored and found in?
  2. Large amounts of histamine is released in?
A

1.)histamine=vasoactive amine derived from the amino acid histadine– “vasoactive” has effects on our blood vessels

  • Mast cells, basophils
    • defends against allergic (immune) rxn’s
  • CNS
    • acts as neurotransmitter
  • Gut regulates gastric acid production

2.) *at any given time we have small amounts of histamine our body b/c it rapidly inactivated by our body

  • allergic/hypersentsitivity rxn
  • tissue injury
  • direct mast cell destruction (drugs/chemicals)
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8
Q
  1. ) Which Histamine receptors are in the CNS?
  2. ) effects of histamine in each “place” of the brain?
  • ACh release →?
  • Alertness→ ?
  • Serotonin→?
  • Food intake→?
  • Emesis center→?
A
  1. ) H1 and H3 and some H2
  2. )
  • ACh release → learning and cognition
  • Alertness→ sleep-wake cycle: makes you alert
  • Serotonin→ mood
  • Food intake→ supression of appetite
  • Emesis center→ N/V
    • why antihistamine is useful in treatment for motion sickness
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9
Q

Four facts about 1st generation H1 antihistamines

A
  • Used to treat allergic symptoms, motion sickness and insomnia
    • available OTC and Rx
  • Poor Receptor selectivity
    • Often interact with other receptors of other amines
      • Anti-muscarinic - tachycardia, constipation, dry mouth
        • Not preferred in elders
      • Anti-alpha adrenergic and anti-serotonin
    • Highly lipophilic
      • crosses BBB to interfere with histaminergic transmission
        • leads to many ADR’s limiting use
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10
Q

Explain the process of an allergic rxn?

A
  1. B-cells converted to active plasma cells
  2. produce IgE
  3. IgE binds to surface of mast cells
  4. Allergen binds to IgE antibodies on primed mast cells
  5. Degranulation of mast cells causes histamine to be released
  6. leads to allergic symptoms
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11
Q

What histamine anatagonists do we have available? What affect do they have?

A
  • Epinephrine
    • smooth muscle relaxation
    • stimulate alpha and beta receptors
      • leads to increased BP as well as bronchdilation
  • Cromolyn sodium -“histamine antagonist”
    • takes a couple weeks to kick in so it would be used as an adjunct with pts. with severve allergies or allergic asthma
    • stabilizes mast cells to prevent degranulation (the release of histamine
  • Antihistamines
    • H1 blockers
      • tx allergies, insomnia, motion sickness- 1st and 2nd generation
    • H2 blockers
      • tx GERD/PUD
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12
Q
  1. What H2 receptor antagonists are more effective than others?
  2. What is their absorption like? Can anything effect their absorption?
  3. Bioavailability of these drugs?
A
  1. All equally effectived and interchangable
  2. Well absorbed- BUT can be delayed with combined with antacid
  3. Bioavailability of cimetidine and ranitidine can be reduced with high doses of antacid
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13
Q

ADE’s of 1st generation H1 antihistamines

A
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14
Q

1st generation H1 blockers

  • Agent name
  • Anti cholinergic effect (is it + or ++ or +++) +++ means strongest
  • Clinical Use and side effects/notes
A
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15
Q
  1. What are the cardiovascular effects of histamine?
  2. Cardiovascular effects of histamine in pts with preexisting structural heart disease or reg. heart disease such as arrythmias, cardiomyopathy?
A
  1. Mast cells present in normal cardiac tissue→ Histamine released during anaphylatic state→enhances influx of Ca2+ into cardiac myocytes →increases contractility (pos. inotrope) → hypotension secondary to vasodilation →tachycardia (compensatory response to hypotension)
  2. These patients have increased expression of mast cells so more histamine would lead to more extreme systemic rxn to the histamine
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16
Q

MOA of H1 and H2 receptor blockers?

A

MOA: block the therapeutic actions of histamine at various receptors throughout the body

17
Q

Histamine in the parietal cells

Gastric acid secretion (HCL) is mediated by? How does the process work ?

18
Q
  1. What is the indictation for H2 receptor antagonists ?
  2. What is their MOA?
  3. What is their onset of action ?
  4. What is their duration of relief ?
A

1.)

  • Indication
    • mild-moderate, infrequent, heartburn
      • ​Good for on-demand, meal provoked symptoms

2.)

  • Reversibly decreases fasting and food stimulated acid secretion by inhibiting histamine on H2 receptor of the parietal cell
    • Reversibly = binds with non-covalent bonds so it can be easily kicked off
  1. ) Onset of action: 30-45 mins
  2. ) Duration of relief: 4-10 hurs
19
Q

Metabolism and DDI’s of 1st gen. H1 antihistamines?

A
  • Metabolism
    • metabolized via 2D6 and 3A4
  • DDI’s with
    • alcohol/benzos/other hypnotics
      • synergistic sedative effect
    • TCA’s
      • QTc prolongation
      • Incrased anti cholinergic effects
    • AChI’s
      • AChI’s increase ACh so it would cancel eachother out and decrease efficacy of drug
20
Q

Antihistamine actions

  • H1
    • Effects of histamine agonism?
    • Effects of histamine antagonism?
  • H2
    • Effects of histamine agonism?
    • Effects of histamine antagonism?
21
Q

DDI’s with 2nd gen H1 blockers

A
  • Fexofenadine
    • not metabolized via CYP 450
      • highest safety profile
    • avoid grapfruit, orange, and apple juice
      • must separate by at least 4 hrs
  • Loratidine, desloratidine
    • metabolized via 3A4 and 2D6
      • watch out for DDI’s wtih ketoconazole and grapefruit juce
  • Ceterizine, levocertirizine
    • DDI’s with grapefruit juice
    • avoid other sedative drugs
22
Q
  1. What is your 1st generation antihistamine
  2. What variety of medical conditions are antihistamines used in?
A
  1. ) Diphenhydramine-1945
  2. )
  • Allergic rhinitis,
  • eczema,
  • urticaria (hives)
  • Insomnia
  • Motion sickness
  • GERD/PID
23
Q

ADE’s of 2nd gen. H1 antihistamines

A
  • somnolence
    • usually at higher doses
    • highest with cetirizine and levocetirizine
  • constipation
  • headache
  • no significant cardiac effects
    • ​safe for patients with pre exisiting cardiovascular disease

Pharm II (12 decks)

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