1. Screening of neuromuscular
blocking agents
By
Arijit Chakraborty
M- Pharm (Pharmacology)
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2. The neuromuscular blocking
agents are used primarily in conjugation
with general anesthetics to provide
muscle relaxation for surgery, while
centrally acting muscle relaxants are
used mainly for painful muscle spasms
and spastic neurological condition.
Neuromuscular blocking agents
can be two types:
a) Depolarization agents.
b) Nondepolarizing agents.
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3. Classification:
A. Depolarizing agents:
Succinylcholine, Decamethonium.
B. Nondepolarizing agents:
1. Long acting: d- tubocuranin
2. Intermediate acting: Vecuronium
3. Short acting: Mivacurium
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4. Models:
• Intact Unanaesthetised Animals:
1. Production of contractures in birds
2. Testing of righting reflex
3. Inclined screen and inverted grid
methods
4. Rotating drum methods
5. Head drop methods
6. Injection into lymph sac of frog
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5. Models:
• Anesthetized Animals:
1. Nerve muscle preparations of
lower limbs
2. Phrenic nerve- diaphragm
preparations
3. Close intra- arterial injection
4. Determination of dose causing
cardiac arrest
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6. Models:
• In vitro studies:
1. Isolated nerve- muscle
preparations
2. Frog nerve- muscle preparations
3. Phrenic nerve- diaphragm
preparations
4. Lumbrical nerve- muscle
preparation in rabbit
5. Ionophoretic micro application
technique 6

7. Intact Unanaesthetised
Animals
Production of contractures in birds:
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1. Administration of depolarization blockers in adult fowls,
chicks causes a rigid extension of the limbs and retraction of
the head.
2. Curare is using for flaccid paralysis of bird,
advantage is this test on avian muscle is the ease with
which the difference in the action of these two groups
of drugs can be strikingly illustrated.

8. Intact Unanaesthetised
AnimalsTesting of righting reflex:
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1. Rat and mice is use for this experiment
to determine the potency of the
neuromuscular blocking agent.
2. Then drug is injected in IP route.
3. Animal is turning on its back and
watching to see if the animal rolls back
over onto its sternum.
4. The rat is on its back when its head is
tilted, its limbs move opposite

9. Intact Unanaesthetised
Animals
Inclined screen and inverted grid
methods:
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1. Mice or rats can also be tested for their
ability to stay on an inverted grid after
administration of neuromuscular blocking
agents.
2. This method is used to estimate
ED50 .
3. Dose given subcutaneously to
groups of 10 mice each.

10. Intact Unanaesthetised
Animals
Rotating drum methods:
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1. Mice is use for this experiment.
2. Mice are place in the rotating drum and noted the
observation time.
3. Drug should be given by subcutaneous route.
4. Place in the rotating drum and noted the falling time.
5. TO calculate the falling time and determine the
Percentage of reduction.

11. Intact Unanaesthetised
Animals
Head drop method:
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1. It is applicable for mouse, rat, guinea pig,
rabbit, dog, monkey.
2. Dose given by intravenous inj. at the rate of 1
ml/ 5 seconds to groups of ten rabbits each.
3. Then the animals are kept in the box where
the head is placed outside in the box.
4. Then observed for the occurrence or
absence of head drop due to muscle
relaxation.

12. Anaesthetized Animals
Phrenic nerve-diaphragm preparation:
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1. The effect of neuromuscular blocking agents on
isolated respiratory muscles may be studied in Phrenic
nerve- diaphragm preparation from rats and guinea pig.
A parallel-sided slip of diaphragm is removed with the
Phrenic nerve.
2. Stimuli are applied alternately to the muscle directly, via
electrodes at each end, and to the Phrenic nerve.
3. Rat diaphragm preparation is relatively insensitive to
Decamethonium and similar agent.
4. Diaphragm from other animals must be from very
young animals or from fetuses so that they enough for
oxygen diffusion.

13. In-vitro Studies
Electrical activity of single muscle fiber:
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1.Frog Sartorius muscle is used.
2. The nerve cut close to its point of entry into the
muscle.
3. The muscle is mounted in a bath of ringer solution
on an illuminated stage and observed from above
with a microscope.
4. The bathe is divided in two groups and the
muscle is drawn through a gap of partition.
5. Stimulating electrodes are placed in the 2
compartment.

14. The recording equipments consists of a DC
amplifier and oscilloscope
A large amount of information can be obtained in
a relatively short time since the process of
mounting and recording from a muscle fibers
takes only a few seconds.
The average values for a large number of fibers
can be determined.
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Electrical activity of single muscle fiber:

15. In-vitro Studies
Lumbrical nerve- muscle preparation in
rabbit:
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1. The rabbit Lumbrical muscle is sensitive to
depolarizing blockers.
2. The lever bearing and writing tip must be chosen
for minimal friction.
3. The lever must be weight loaded to stretch the
muscle optimally and ensure a linear relation between
the height of the recording and the work done on the
lever by the muscle.
4. The preparation is very sensitive to changes in
ionic concentration.

16. In-vitro Studies
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6. A fall in the concn of H2 , Ca, Mg especially, Ca
induces spontaneous activity.
7. Respectively response to stimulation and
irregularity of behavior, while altering the
sensitivity to all types of blocking agents.

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