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Pharm Unit 2 > Histamine, 5-HT, and Antagonists > Flashcards

Histamine, 5-HT, and Antagonists Flashcards

1
Q

autacoids are …

A

substances produced by neural and non-neural tissues which act locally to modulate activity of smooth muscle, nerves, glands, platelets, etc; regulate aspects of GI, uterine, renal function and involved in pain, fever, inflammation, allergic reactions, asthma, thromboembolic disorders, etc

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2
Q

Where is the largest concentration of histamine found?

A

skin, lungs, GI, nasal mucosa, blood

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3
Q

Where is histamine stored and synthesized? Ie what types of cells.

A

storage - bound to proteoglycan in granules in mast cells and basophils
synthesis - rapidly in response to correct stimuli in paracrine cells of gastric fundus and histaminergic neurons

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4
Q

What stimuli cause mast cells to degranulate? Examples?

A
  1. antigens and anaphylatoxins (via crosslinking of IgE; Ca mediated)
  2. certain basic drugs (probably dec GTP; examples codeine, morphine, tubocurarine, Ach)
  3. chemical or mechanical injury (increased Na; insect, snake venom, cuts)
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5
Q

Distribution and mechanism of H1 receptor.

A

smooth muscle, endothelium, brain

Gq

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6
Q

Distribution and mechanism of H2 receptor.

A

gastric mucosa, cardiac muscle, mast cells, brain

Gs

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7
Q

Distribution and mechanism of H3 receptor.

A

presynaptic: brain, myenteric plexus, other neurons

Gi

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8
Q

Distribution and mechanism of H4 receptor

A

eosinophils, neutrophils, CD4 T cells

Gi

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9
Q

What’s the really important physiologic effect of histamine in the cardiovascular system?

A

fall in BP due to vasodilation - pronounced drop, anaphylactic shock
there’s also an increase in vascular permeability and decrease in HR

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10
Q

What effect does histamine have in the lungs? Who does this affect most?

A

bronchoconstriction; hyperreaction in asthmatics

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11
Q

Effects of histamine in GI tract? Which receptors?

A

contraction of sm muscle - diarrhea H1

secretion of acid, pepsin, intrinsic factor H2

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12
Q

Effects of histamine on sensory nerve endings in the skin?

A

pain (dermis) and itching (epidermis) H1

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13
Q

What’s the role of H3 receptors in the brain?

A

autoreceptors; feedback inhibition on histaminergic neurons to stop synthesis and release

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14
Q

What are the three ways to reduce the effects of histamine?

A
  1. physiological antagonists (epi) that have opposite actions (on diff receptors)
  2. release inhibitors - reduce degranulation of mast cells
  3. histamine receptor antagonists
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15
Q

Class and action of diphenhydramine.

A

H1 antagonist; ethanolamine derivative

antimuscarinic effects; sedation

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16
Q

Class and action of tripelennamine.

A

H1 antagonist; ethylenediamine derivative

moderately sedating, OTC sleep aids

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17
Q

Class and action of cyclizine.

A

H1 antagonist; piperazine derivative

dramamine; anti-motion sickness

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18
Q

Class and action of promethazine.

A

H1 antagonist; phenothiazine derivative

antimuscarinic effects, marked sedation, antiemetic

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19
Q

Class and action of chlorpheniramine.

A 
H1 antagonist; alkylamine derivative
less sedating (daytime) cold meds
20
Q

Class and action of loratidine and fexofenadine

A

H1 antagonist; piperadine derivatives
newest class; 2nd generation
don’t cross BBB - no sedation
longer duration - once a day dosing

21
Q

Class and action of azelastine

A

H1 antagonist; 2nd generation
intranasal for allergic rhinitis
ophthalmic solution for allergic conjunctivitis

22
Q

Class and action of cetirizine.

A

H1 antagonist; 2nd generation

high grossing - zyrtec

23
Q

Clinical uses of H1 antagonists.

A
  1. allergic reactions - allergic rhinitis, urticaria, conjunctivitis, topically for insect stings
  2. motion sickness
  3. nausea and vomiting of pregnancy
  4. ‘sleep aids’
24
Q

Adverse effects of H1 antagonists

A
  1. sedation (impaired cognitive function)
  2. anti-muscarinic (blurred vision, dry mouth, urinary retention, constipation)
  3. poisoning - esp children; convulsions at high doses
  4. allergy (esp with topical)
  5. local anesthesia (high conc)
  6. ventricular tachycardia with high dose of piperadines
25
Q

What are the H2 antagonists?

A

cimetidine, ranitidine, famotidine, nizatidine

26
Q

Mechanism of H2 antagonists?

A

compete at H2 receptors in parietal cells; block gastric acid secretion (effect more pronounced on nocturnal than post meal)

27
Q

Clinical use of H2 antagonists?

A

dyspepsia (OTC)
duodenal and gastric ulcers
hypersecretory conditions (zollinger-ellison syndrome caused by gastrin-secreting tumor)

28
Q

Adverse effects of H2 antagonists?

A 
very rare (1-3% of pts)
CNS dysfunction (slurred speech, confusion; elderly)
antiandrogen (cimetidine - gynecomastia, impotence)
liver toxicity (ranitidine)
P450 inhibition (cimetidine - potentiates action of other drugs; nizatidine doesn't do this!!!)
29
Q

What amino acid is 5-HT derived from?

A

tryptophan

30
Q

Distribution of 5-HT in the body?

A

GI tract (90% enterochromaffin cells)
platelets (8%)
CNS (2%)

31
Q

There are a lot of 5-HT receptors. What are most of them? What’s the one exception?

A

most are GPCRs; 5HT-3 is a ligand-gated cation channel

32
Q

Actions of 5-HT in GI tract?

A

contraction of smooth muscle;

not carcinoid syndrome - enterochromaffin tumors release large amounts

33
Q

Actions of 5-HT in cardiovascular?

A

vasoconstrictor in smooth muscle, vasodilate in skeletal muscle and heart
reflex bradycardia
platelet aggregation

34
Q

Actions of 5-HT in nervous system?

A

peripheral - pain and itching; activator of chemosensitive endings in coronary vascular bed
central - mood, food intake, sleep, regulation of pituitary secretions; presynaptic autoreceptors

35
Q

Cyproheptadine is both antihistaminic and antiserotinergic. What are its uses and side effects?

A

Use:
skin allergies, urticaria (anti-H1)
diarrhea of carcinoid (anti-5HT2)
Side effects - sedation, antimuscarinic

36
Q

Ketanserin isn’t marketed in the US yet, but what is it used for in other countries?

A

antihypertensive (relaxes vascular and tracheal sm muscle)

antagonizes platelet aggregation

37
Q

What receptor does ondansetron block? What’s it used for?

A

5-HT3 antagonist;

prevention of N/V associated with chemo

38
Q

Ergot alkaloids work at a whole bunch of receptor types - what are they?

A

agonist and antagonist at serotonin and alpha-adrenergic; some dopamine agonists too

39
Q

In general, ergot alkaloids have actions in the CNS, vascular sm muscle, and uterine sm muscle. What are these effects?

A

CNS - powerful hallucinations
Vascular sm muscle - vessel constriction - prolonged and powerful
Uterine sm muscle - prolonged contraction

40
Q

What ergot alkaloids are used in the Tx of migraines?

A

ergotamine and methysergide

triptans (not ergot)

41
Q

When can ergotamine be helpful? Side effects?

A

given during prodrome of migraine;

side effects - N/V, prolonged vasoconstriction

42
Q

Methysergide is only used for migrain prophylaxis. What are it’s side effects?

A

GI disturbances, inflammatory fibrosis fr chronic use, occasional hallucinations

43
Q

The triptans are also useful for migraine treatment, but aren’t ergot alkaloids. What are the possible mechanisms for how they work?

A
  1. activate 5-HT1B,D receptors - vasoconstriction of cerebral vessels, relieving the dilation that contributes to throbbing HA
  2. stimulate presynaptic receptors (same type) on trigem nerve endings, inhibiting release of pro-inflammatory neuropeptides
44
Q

What is ergonovine used for?

A

sustain uterine contraction to treat postpartum hemorrhage

45
Q

Bromocriptine is an ergot alkaloid that acts as a D2 dopamine agonist in the treatment of what?

A

hyperprolactinemia - suppresses prolactin secretion from pituitary cells

Pharm Unit 2 (10 decks)

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