3 Introduction Pain an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage Analgesics Drugs used to relief or suppress the pain ID: 908746
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Slide1
ANALGESIC DRUGS
#
PHL 322, Lab.
3#
Slide2Introduction
- Pain:
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
- Analgesics :
Drugs used to relief or suppress the pain.
Slide3pain is associated with electrical activity in small diameter primary afferent fibers of peripheral nerves .
These nerves have sensory ending in the peripheral tissues and activated by noxious stimuli of various kinds :
Chemical stimuli
Thermal stimuli
Mechanical stimuli
Slide4Types of afferent sensory nerve fibers :
C- fibers
A
- fibers
Non
-
myelinated
Myelinated
Low conducting velocity
High
conduction velocity
Cause
a dull burning and non-localized pain
Cause a sharp and localized pain
Slide5Nociceptors
A Sensory receptor that
sends signals that cause the perception of
pain
in response to a potentially damaging
stimulus.
These receptors are activated by mechanical, thermal and chemical stimulants.
Provide information about the location, intensity and duration of a noxious stimulus to the body
Nociceptors are connected to primary afferent nerve fibers.
Slide6Pain Mediators
pain mediators include :
bradykinin
,
leukotriene
, substance P, histamine, Ach, 5-HT and prostaglandins
they increase the sensitivity of the nerve ending to other pain mediators
Pain Mediators
Mechanism of action of the
paim
mediators to cause pain :
Direct :
stimulate of the nerve ending directly via
nocieceptors
.
Indirect :
increase the sensitivity of nerve ending to other pain mediators.
Slide8Analgesics are divided into
Narcortic
analgesics
(
opioid
analgesics )
e.g.
Morphine
Non- narcotic analgesics
( non-
opioid
analgesics )
( non- steroidal
anti-inflammatory drugs )
NSAIDs
e.g.
Aspirin
Slide9Opioid analgesics
Opioid include natural (
Morphine
),
semisynthetic
(
Heroin
) and synthetic (
Fentanyl
).
They reduce moderate to severe pain without loss of consciousness.
They act by binding to specific receptors located primarily in the brain and spinal cord.
Slide10Opioid analgesics
The major classes of
opioid
receptors are(
μ
,
κ
,
δ
) mu, delta and kappa.
Each receptor type has subtypes: mu1, mu2, delta1, delta2, kappa1, kappa2 and kappa3.
Most of the currently available
opioid
analgesics act primarily at the mu receptor.
Slide11Mechansim
of action :
All
opioid
recptors
are linked through G-
proiten
by inhibition of
adenylate
cyclase
i.e
facilitate opening of K channels (
causing
hyperpolarization
) and inhibit opening of Ca channels ( inhibiting transmitters release )
They stimulate the release of endogenous
opioid
peptide (
endorphins and
enkephalins
) which cause
decresing
in release of pain mediators.
Slide12Side effects:
Dependency
and
tolerance
Nausea and
constipation
CNS:
drowsiness, lightheadedness, euphoria or
dysphoria
, or confusion.
Urinary retention
Respiratory depression
, particularly in elderly or debilitated patients
Miosis
(
constriction of the pupil
)
Slide13Non opioid
analgesics (
NSAIDs
)
Aspirin and other NSAIDs are useful for the treatment of pain from injury (
mild to moderate
)
Examples for NSAIDs :
Cox (
cyclooxygenase
) non selective :
Aspirin, Ibuprofen,
Diclofenac
…etc
Cox2 selective :
Celecoxib
and
Rofecoxib.
Slide14Phospholipids
Phospholipase
A
2
Arachidonic Acid
Prostaglandins
Thromboxanes
Prostacyclin
COX
Leukotrienes
Lipoxygenase
Slide15LAB WORK
Objective :
To show the analgesic effects of different analgesics using different methods.
Writhing test.
Hot plate method.
Slide16Writhing test
Principle
:
Pain is induced by injection of noxious chemical as Acetic acid 0.1% at volume 0.3 ml.
Writhing means stretching behavior of the abdominal and at least one hind limb.
Slide17Procedure:
1.First inject the mouse with acetic acid and calculate the number of writhing/20 minutes and this will be control test.
2.Inject the second animal with aspirin and inject the third one with morphine.
3.After 5 minutes inject the animals with acetic acid then calculate the number of writhing/20 minutes.
Slide18Procedure:
4.Compare the number of writhing for each drug and comment on the results (a drug has less number of writhing >>> more potency as analgesic
.
Slide19Drug
No. of writhing/20 minutes
Control
Acetic cid
Test 1
Morphine acetic acid
Test 2
Aspirin acetic acid
5 min’s
5 min’s
Slide20Hot plate method
principle:
The paws of the mouse are very sensitive to heat at temperature which are not damaging the skin .
At temperature of 55 C
the mouse will jump and licking the paws.
The time till these response occur is calculated and is prolonged after administration of analgesics.
Procedure:
Put the mouse on the hot plate and record the time taken in order to jump or licking the fore paws.
Record the time in seconds this is the control time.
Weight the animal and calculate the dose of Morphine and Aspirin
At 5 min’s interval ( for 30 min’s ) place the animal on the hot plate and record the time to see the response .
Compare the time need to see the response the drug with longer time is more potent as analgesic.
Slide22Drug
Time interval
zero
5
10
15
20
25
30
Morphine
aspirin
Slide23Conc (g%)
Dose mg/Kg
Morphine
0.2%
20
aspirin
3%
300