Bronchial asthma is characterized by both bronchoconstriction and airway inflammation which leads to bronchial hyperresponsiveness to various stimuli. Different mediators are implicated in asthma. As the precise etiology is not known and multiple biochemical processes are triggered by different causative factors, it is difficult to have a single drug which can effectively and simultaneously act upon different mediators. This led to an intense search for potent and safe antiasthmatic drugs. This presentation intends to compile different screening methods for the evaluation of new candidate drugs with potential for the treatment of asthma. These include in vitro, in vivo, receptor binding and enzymatic methods.

1. Preclinical screening of anti-
asthmatic drugs
PRESENTED BY: UNDER GUIDANCE OF:
SHUBHAM P. KOLGE Ms. VAIBHAVI N. GARGE
M. PHARM FIRST YEAR ASSISTANT PROFESSOR.
PHARMACOLOGY PHARMACOLGY DEPARTMENT

2. Introduction
Asthma: Bronchospasm or bronchoconstriction results when
the lung tissue is exposed to extrinsic or intrinsic factors that
stimulate a bronchoconstrictive response. Bronchial asthma
is characterized by hyper responsiveness of trachea
bronchial smooth muscle to a variety of stimuli, resulting in
narrowing of air tubes, often accompanied by increased
secretion, mucosal edema and mucus plugging. Causes:
humidity, air pressure changes, temp. changes, smoke,
fumes, stress, emotional upset, allergies, dust, food, some
drugs Symptoms : include dyspnoea, wheezing, cough.

3. Types of asthma
1. Asthma associated with specific allergic reaction.
2. Asthma associated with known allergy.
3. Asthma associated with COPD.
4. Exercise induced asthma.
some patients develop wheeze that regularly follows within a
few minutes of exercise.

4. Bronchodilators
Bronchodilators::
Bronchodilators: The pharmacological therapy of
asthma employs drugs aimed more directly at
decreasing bronchospasm (i.e. bronchodilation) The
main drugs used as bronchodilators are β 2 -
adrenoreceptor agonists, other include xanthenes,
cysteinyl leukotriene receptor antagonists and
muscarinic receptor antagonists.

9. In vitro methods
1. Binding assay
2. Histamine receptor assay
3. Cell culture method
4. Test in isolated organs
5. Spasmolytic activity in guinea pig lungs
6. Vascular & airway responses to isolated lung
7. Reactivity of isolated perfused guinea pig trachea

10. Spasmolytic activity in isolated guinea pig
lung strips
● Purpose and rationale:- to check the spasmolytic
activity induced by histamine and calcium ionophores.
● Animal: albino guinea pigs
● Sex: m/f
● Weight: 300-450g

11. Procedure
Lungs isolated & Cut into strips of 5cm in PSS
Mounted in organ bath
Spasmogen is added for 30-60 min
2 preload readings taken & spasmogen added again
Add test drug after 5 min

12. Evaluation
%inhibition of spasmogen induced contraction is
calculated.
measure the percentage inhibition of spasmogen
induced contraction is calculated
Cont.....

13. Vascular and airway responses in
isolated lung
Animal: sprague-dawley rats
Weight: 300-350g
Rationale: To measure and compare
1) Pulmonary arterial pressure
2) Airway pressure
3) Reservoir blood level

14. Procedure
Rats anesthetized by pentobarbital sodium
Trachea cannulated and animal on artificial respiration
Rats heparinized with 1000 units of i.v heparin & blood
withdrawn from carotid artery
Lungs removed and suspended in water jacketed
chamber

15. Cont….
Pulmonary artery catheterized
Lungs perfused with Krebs Henseleit solution
Changes in parameters are recorded after addition of test
drug and compared with baseline

17. Evaluation
changes in pulmonary arterial pressure after
injection of test drug are measured in mmHg and
compared with baseline values.

18. In vivo methods
1. Brochospasmolytic activity in anaesthetized guinea
pigs
2. Arachidonic acid/PAF induced respiratory vascular
dysfunction
3. Anaphylactic microshock
4. Serotonin aerosol induced asphyxia
5. Histamine induced bronchoconstriction
6. Pneumatochography in guinea pigs
7. Bronchial hyperactivity in guinea pigs
8. Mast cell stabilising activity in rat mesentery

19. Bronchospasmolytic activity (Konzett
Rosseler method)
Animal used: Guinea pig
Anaesthetic used : urethane i.p.
Principle: Bronchospasm causes decrease in volume of
inspired air & increase in volume of excess air
Rationale: To measure volume of air not taken up by lungs
after brochospasm

22. Procedure
Trachea is cannulated
ARM 1 - connected to respiratory pump
ARM 2- connected to statham pressure transducer
Artificial ventilation at frequency 60 strokes/min is
maintained

23. Cont…. Excess air not taken up by lungs is measured
Test drug administered (through jugular vein)
BP recorded (from carotid artery)
Each animal placed in plastic containers
(Histamine chamber)

24. cont….
0.25% histamine solution aerosol sprayed at 180 mmHg
5 mins exposure time (Test drug given orally 1 hr before exposure)
Spasmogen challenge is repeated
Unprotected animals fall on their sides

25. Evaluation
🞇Results are expressed as percent inhibition of
induced bronchospasm over the control agonistic
responses.
🞇The ED50 value is calculated.

26. Arachidonic acid/PAF induced respiratory vascular
dysfunction
Animal used : Guinea pigs
Anaesthetic used : Pentobarbitone sodium
Rationale: To study & compare
1. % inhibition or increase of brochospasm
2. BP reduction (measure magnitude and duration)
3. Thrombocytopenia & haematocrit

27. Principle
1. Arachidonic acid-metabolized into TXA2 and PGI2.
2. Thromboxane - causes bronchospasm &
thrombocytopenia
3. prostacycline - causes decrease in SBP & DBP
1. PAF - causes bronchoconstriction, thrombocytopenia,
leukocytopenia, reduction of BP and increase of
hematocrit.

28. Procedure
1. Trachea - artificial respiration (70-75 strokes/min)
2. Jugular vein - test drug
3. Carotid artery - blood withdrawal & transducer
attached for BP measurement
Record BP & changes in airflow
Animal given multiple iv injections of arachidonic acid till 2
bronchospasm of equal intensity are obtained

29. cont…..
Test drug administered intravenously
Repeat spasmogen injections

30. Evaluation
1. % inhibition or increase of bronchospasm, reduction in
BP, thrombocytopenia, leukocytopenia and hematocrit
after test drug administration is calculated in comparison
to control values before drug treatment.
2 .From the patern of profile of influence on
bronhoconstriction, thombocytopenia and BP reduction, the
mechanism of test drug is concluded.

31. Conclusion
1. Various categories of agents are employed in the
symptomatic relief of Asthma such as β2 agonist,
antimuscarinic, antihistaminics, anti-inflammatory
corticosteroids, antiallergic etc.
2. In this presentation, we have tried to cover most of
categories of agents in the screening models for the
evaluation of antiasthmatic activity.
3. Probable mechanisms related to these screening
models are also discussed here.

32. Reference
1. Drug Discovery and Evaluation: pharmacological
assays by H Gerhard Vogel
2. Preclinical models of asthma and COPD
(stevenson and Belvisi)
3. Screening methods in pharmacology: by
Robert Turner.