1.General 2. Classification 3. Screening Models : Principle Procedure Evaluation Modification 4. Reference

1. SCREENING MODELS
FOR ANALGESIC
ACTIVITY
Submitted to : Dr Manjusha Choudhary
Submitted by : Diksha
M.Pharmacy 1st yr
Roll No. 12

2. CLASSIFICATION
OPOID ANALGESIC
(a)Natural opium alkaloids:-
Morphine
Codeine
(b) Semi synthetic opiates:-
Diacetylmorphine
Oxymorphine
(c) Synthetic opoids:-
Pethidine
Fentanyl
Tramadol
NSAID
(a) Non selective cox
inhibitor
(b) Prefarential cox
inhibitor
(c) Selective cox-2
inhibitor
(d) Analgesic
antipyretic with poor
anti inflammatory
drug

3. NSAIDS
(a) Non- selective cox inhibitor :-
1. Salicylates :- Aspirin, Sodium salicylate, Sulfasalazine
2. Propionic acid derivatives :- Iburefen, Ketoprofen, Fenoprofen
3. Anthranilic acid derivatives :- Mefanamic acid, Tolfenamic acid
4. Aryl acetic acid derivative :- Diclofenac,Fenclofenac
5. Oxicam derivative :- Piroxicam, Tenoxicam
6. Pyrole pyrolidine derivative :- Ketorlac
7.Indole derivative :- Indomethacin
(b) Prefarential cox inhibitor :- Nimusulide, Meloxicam
(c) Selective cox-2 inhibitor :- Celecoxib, Rafecoxib
(d) Analgesic with poor anti inflammatory action:-
1.Para amino phenol derivative :- Paracetamol
2. Pyrazole derivative :- Propiophenazone
3. Benzoxazocine derivative :- Nefopam, Diacerin

4. SCREENING MODELS
1. RADIENT HEAT METHOD
2. TAIL FLICK METHOD
3. HAFFNER’S CTAIL LIP METHOD
4. FORMALIN TEST

5. RADIENT HEAT METHOD
 PRINCIPLE : This method was develped by
Schumacher et al (1940), Wolff et al (1940)
for quantitative measurement of pain
thershold. This method is used to evaluate
analgesic activity in animals by measuring
drug induced changes in senstivity of mice to
heat applied to their tails.

6. PROCEDURE
• Number and weigh the group of 10 mice, weight about 18-22
gm.
• Before administration of test compound/ satndard, animal is
put into small cage with an opening for the tail at the rear
wall.
• The tail is held gently the investigator.By opening the shutter,
a light beam radient heat is directed itno the proximal of tail.
• For about 6 sec raection of animal is observed. The mice tries
to pull their tail away and turn the head.
• Mice with reaction time of more than 6 sec are not used.
Simple tail flick as a end point of this test.
• The animals are submitted to the same testing procedure
after 30,60,90,120 mins.

7. EVALUATION :-
The average values of the reaction time after each time interwal
are calculated and compared with pre test value by analysis of
significance.
As standard codeine, morphine can be used. The ED50 values of
these drugs are- Codiene : 12 mgkg s.c.
Morphine : 2 mgkg s.c.
 MODIFICATION:- Carmon and Frostig(1981) used
brief laser induced heat applied to the rat ear for
pharmacological testing of analgesics.

8. TAIL FLICK METHOD
• PRINCIPLE:-This method is based on
the morphine like drugs are
selectively capable of prolonging the
reaction time of tail withdrawal
reflux in rats induced by immersing
the end of tail in warm water of 55 C

9. PROCEDURE
• Weigh and number the animals
• Animals are placed into individual cage leaving
the tail hanging out freely for 30 mins before
testing.
• The lower 5 cm portion is marked. The marked
part of tail is immersed in a cup of freshly filled
water of temp 55 C (exect).
• The reaction time is determined before and after either
oral s.c. administration of test substance i.e. after
30,60,90,120 mins.
• The cut off time of the immersion is 15 sec.

10. EVALUATION
ED50 value can be calculated for each compound and
time response curve can be measured. All the
morphine like analgesic have been shown to be
active at dose which do not produced gross
behavioural changes.
e.g. An ED50 of 3.5 mgkg s.c. for morphine
An ED50 OF 1.7 mgkg s.c. methadone was
found to be active.

11. MODIFICATION
• Tiseo et al (1988) could shows that the
endogenous kappa agonist dynorphin was
inactive in the rat tail immersion test at 55*C,
but gave the dose response curve in the cold
water of the test.

12. HAFFNER’S TAIL CLIP METHOD
PRINCIPLE :- The method was described as
early as 1929 by Haffner’s who
observed the raised tail in mice treated with
morphine or similar opioid drugs and found
the tail after drug treatment to be less
sensitive to noxious stimuli.

13. PROCEDURE
• Weigh and number the male mice with a weight
between 18 and 25 gm.
• An artery clip is applied to the root of the tail of mice
and reaction time is noted for each mice.
• The test compound is administered s.c. to fed mice
and orally to fasted animals.
• An artery clip is applied to the root of the tail (approx
1 cm from the body) to induce pain.
• The animals quickly responds to this noxious stimuli by
bitting the clip or the tail near the location of clip.
• The time between the stimulation onset and response
is measured by a stopwatch.

14. EVALUATION
A cut off time is determined by taking the average
reaction time plus 3 times the standard deviation of
the combined latencies of the control mice. Any
reaction time of the test animals which is greater than
the cut off time is called +ve response.
e.g. ED50 value for morphine : 1.5 mgkg s.c.
ED50 value for codeine : 7.5 mgkg s.c.
MODIFICATION :- Takagi et al (1966) published a
modification of Haffner’s method
for testing analgesics.

15. FORMALIN TEST IN RATS
PRINCIPLE :- The formalin test in rats has been
proposed as a chronic pain model
which is sensitive to centrally active analgesic
agents by Dubuisson and Dennis (1977).

16. PROCEDURE
• Number and weigh male wistar rats weight about 180-
300 gm .
• Each individual rat is placed into a clear plastic cage for
observation.
• Injected 0.05 ml of 10 % formalin into the dorsal
portion of the front paw. The responses are noted.
• The test drug is administered either s.c. or orally.
• Readings are taken after 30,60,90,120 mins , according
to pain scale.
• Pain responses are indicated by excessive licking and
bitting of the paws.

17. EVALUATION
Using various doses, ED50 value for protection
can be calculated. Dose of 1.7 mgkg s.c. for
morphine and 15 mgkg s.c. for pethidine was
found to be effective.

18. MODIFICATION
Herman and Felinska (1979) proposed a rapid
test for screening of narcotic analgesic in mice
by evaluation of behavioural symptoms after
s.c. injection of EDTA.

19. REFERENCE
• H.Gerhard Vogel “Drug Discovery and
Evaluation, Pharmacological Assays”, Page No
• Kulkarni S.K. ‘’Handbook of Experimental
Pharmacology”, Page No. 137-141

20. THANK YOU….