Autacoids (histamine)

Question 1

What is the action of Histamine in B.Vs

Answer 1

H1 receptor located on B.Vs
1- when activated
2- it activate Endothelial derived relaxing factor (EDRF)
3- EDRF diffuse in Smooth musc. and activates guanylcyclase
4- Guanylcyclase increase the level of cGMP
5- produce smooth musc. relaxation
V.D

in H1 it is rapid onset and short duration
In H2 it is slow in onset and more sustained

Question 2

What is the effect of histamine on H1 receptors on

a) non vascular smooth muscle
b) the heart
c) the nervous system

Answer 2

a) It produces contraction
b) it slows the A/V conduction
c) it produces itching and pain

Question 3

H1 receptors are blocked by H1 antagonist as

Answer 3

Chlorpheniramine

It produces sedation as it crosses the BBB

Question 4

Effect of histamine on H2 receptors on

a) gastric mucosa
b) B.Vs
c) heart

Answer 4

A) increase acidity
B) V.D slow in onset and more sustained
C) positive chronotropic and inotropic

Question 5

H2 antagonist

Answer 5

Cimetidine

Question 6

Effect of histamine on H3 on presynaptic neuron of CNS ,CVS , GIT , Bronchial smooth muscles

Answer 6

It reduces the release of histamine from histaminergic neurons

Question 7

H3 antagonist

Answer 7

Thiperamide

Question 8

Where histamine receptors locate

Answer 8

H1
on B.Vs ,heart and CNS

H2
on gastric mucosa , B.Vs and heart

H3
Presynaptic neuron

Question 9

What is the effect of histamine on

a) heart
b) B.Vs
c) non vascular smooth muscles
d) exocrine gland
e) nerve ending

Answer 9

A) positive inotropic and chronotropic .
Negative dromotropic
B) V.D and increase permeability
C) contraction and cause B.C
D) increase secretions and increase acidity of stomach
E) stimulate nerve ending causing itching and pain

Question 10

Histamine antagonists

Answer 10

1- physiological antagonism — adrenaline
2- pharmacological antagonism — competitive antagonism
3- preventing release — by steroids and cromolyn sodium

Question 11

H1 antagonists effects

Answer 11

1- affect vascular( V.D) and non vascular(contraction) smooth muscles but its effect on bronchial asthma is minimal because of leukotrienes
2- the first generation drugs cause sedation but the second generation does not penetrate BBB so no sedation
3- treat motion sickness as it has anticholinergic action
4- local anesthetic and antipruritic

Question 12

H1 drugs not cross BBB and not affect muscarinic receptors

Answer 12

fexofenadine and loratidine

Question 13

What are the side effects of H1 antagonists

Answer 13

1- Sedation dizziness tennitus lassitude fatigue nervousness insomnia and tremors
2- nousea vomiting and gastric distress
3- atropine like effect ( اعراض زغلولة )
4- overdosage cause excitation , hallucination excitement ataxia and convulsions
5- allergic manifestations when given topically

Question 14

Therapeutic uses of H1 antagonists

Answer 14

1- allergic disorders . Given with epinephrine

2- in motion sickness and vesitular disturbances as menieres disease

Question 15

What is more effective in motion sickness

Answer 15

Scopolamine

Question 16

First generation H1 antagonists and their effect

Answer 16

1- diphenyldramine

2- Dimenhydrinate

3- promethazine

4- chlorpheniramine

Cause sedation and anticholinergic effect

Question 17

What are second generation H1 antagonists and what are the differences between them and first generation drugs

Answer 17

1- fexofenadine
2- loratadine

No sedation
No anticholinergic effect

Question 18

What are H2 antagonist drugs and how they work

Answer 18

Ranitidine
Cimetidine
Famotidine
Nizatidine

The block the effect of histamine on gastric mucosa

Question 19

What are the pharmacokinetics of H2 blockers

Answer 19

H2 blockers are well absorbed when given orally

The bioavailability of all drugs is 50% however the bioavailability of nizatidine is 90%

Question 20

Why cimetidine is not used today

Answer 20

Cuz of its side effects
1- on CNS : headache , dizziness and confusion
2- it increases serum prolactin leading to antiangrogenic effects . Reduce estrogen catabolism in men may cause gynecomastia , galactorrhea and loss of libido in females .
3- leucopenia and elevated serum creatinine level
4- it inhibits the activity of cytochrome p450 in liver thus prolong other drugs duration as warfarin, phenytoin, propranolol, nifedipine and theophylline and decreases liver blood flow

Question 21

What are the therapeutic uses of H2 blockers

Answer 21

1- gastric mucosa
2- in esophageal reflux
3- preanesthetic as it rduce aspiration of gastric contents
4- prophylaxis of stress ulcers and it is given IV