1. Analgesics
Lab # 3

2. Types of Pain - Stimulation of skin & mucous membranes
Superficial:
- Stimulation of skin & mucous membranes
- Fast response
Deep:
- Arises from muscles, joints, tendons, heart ..etc.
- Slow response

3. Analgesics Definition Classification
Drugs that selectively inhibit the perception (sensation) of the pain
Classification
1- Peripheral (miscellaneous):
- Causal
- Non-causal
2- Central:
- Narcotic
- Non-narcotic

4. Peripheral Analgesics
Causal
-Treat the cause
Example:
Atropine (antispasmodic)
Non-causal
- Not treat the cause
Examples:
1- Local anaesthetics (for superficial tumor)
2- Counter-irritant (apply pain that counteract or mask the original one e.g. acupuncture)

5. Central Analgesics Narcotics Non-narcotic
The class - Opioids (morphine &
morphine like drugs)
Examples Natural (as codeine)
2- Semi synthetic e.g.
di-hydromorphine&
diacetylmorphine (heroin)
3- Synthetic e.g. pethidine
4- Endogenous opiates as
endorphins & encephalins
Non-narcotic
- NSAID
1- Aspirin
2- Paracetamol
3- Diclofenac
4- Piroxicam
5- Ibuprofin
6- Ketoprofin

6. Central Analgesics Narcotics Non-narcotic Site of Cortex & thalamus
action
Antagonist Naloxone, nalorphine
& levallorphan
Uses Sever & deep pain e.g.
cancer, MI & anginal pian
Potency High
Side effect Addiction
MOA
‡ of opiates receptors
(m, k ,s, d) and relief the
pain through the release of
endorphines & encephalins
Non-narcotic
Subcortical “thalamus”
No antagonist
Dull pain e.g. headache, toothache & backache
Low
No addiction. ↑in bleeding tendency & ulcer
Inhibits prostaglandin synthesis
by inhibition of cycloxygenase
enzyme

7. Screening Methods For Analgesics
Principle
Pain is induced to a suitable animal and the response of the animal to the painful stimuli is recorded before and after administration

8. Screening methods Narcotics: 1- Thermal method a- Hot plate
b- Tail flick
2- Mechanical method

9. Screening methods Non-narcotic: 1- Electrical method
2- Chemical ( Writhing method)

10. Hot – plate Material Animal: Mouse
Instrument: Hot plate analgesiometer
Painful stimulus: Heat (55°C)
Drug used: Morphine

11. Tail-flick Material Animal: Mouse
Instrument: Tail-flick analgesiometer
Painful stimulus: Heat (by apply a beam of light 130°C)
Drug used: Morphine

12. Writhing Method Principle:
The painful stimulus is induced by IP injection of an irritant substance (e.g. acetic acid)
Writhing:
Stretching of the body, withdrawing of the limb, retraction of the abdomen & the stomach touches the ground

13. Writhing Method Material Animal: Mouse
Painful stimulus: Chemicals e.g. acetic acid
Drug used: NSAID e.g. Na salicylate
Drug
Onset of writhing
No. of writhing
Acetic acid (control)
Na salicylate (100mg/kg)
Na salicylate (200mg/kg)