ANALGESICS
PAIN
Pain receptors are nerves
that transmit pain.
Respond to thermal,
mechanical and
chemical stimuli.
Impulse generated.
Arrives at spinal cord and
brain (CNS).
Prostaglandins and
leukotrienes make pain
receptors more
sensitive.
ANALGESICS
Drugs that relieve pain.
Mild analgesics (aspirin,
Paracetamol, Ibuprofen)
Non-addictive.
Strong Opiates (morphine,
heroin, codeine)
Addictive (controlled
substances).
Local anaesthetics (lidocaine
in dentistry)
General anaesthetics
(unconsciousness,
insensitivity)
MILD ANALGESICS
Indirectly blocking
enzymecontrolled
synthesis of
prostaglandins.
Reduce pain, fever
and
inflammation.
NATURAL PAINKILLERS
Endorphins and
enkephalins
Bind to neuro-receptors
in brain relieving pain.
Strong analgesics
(opiates) work by
binding to opiate
receptors in brain,
preventing
transmission of pain
imulses.
DIFFERENT MECHANISMS…
ASPIRIN
MORPHINE
Works by acting on
inflammed tissue and
associated nerves.
Acts directly on brain.
USES OF DERIVATIVES OF SALICYLIC ACID
Mild analgesic (aches,
pains, headaches,
sunburn, arthritis)
Anti-pyretic (reduces
fever)
Anti-inflammatory
agent.
Anti-platelet agent
(prevention of blood
clotting after heart
surgery)
PREVENTION OF BLOOD CLOTTING
Results from inhibiting
production of
prostaglandins.
These are hormone-like
fatty acids that cause
blood platelets to stick
together (clot)
Found to prevent
recurrance of heart
attacks in moderate
amounts.
DISADVANTAGES OF ASPIRIN
Stomach upset and internal bleeding , ulceration – due to acidity.
Gastrointestinal bleeding following alcohol use.
Skin rashes, respiratory difficulties (for 0.5%)
Accidental poisoning in infants.
Reye’s syndrome in children (liver and brain disorder)
SUBSTITUTES EXIST…
PHENACETIN
ACETAMINOPHEN
USES OF ACETAMINOPHEN….
Like aspirin, an anti-pyretic reducing fever.
As an analgesic to reduce mild pain.
Does not upset stomach, but is not an effective anti-inflammatory drug.
Safe, preferred drug for those with aspirin allergy.
Not to be taken with alcohol.
Overdose (>20 tablets) can be serious (brain damage, death)
IBUPROFEN
Same effects as
aspirin.
Fewer stomach
problems.
Wide safety margin.
Kidney problems in
large doses.
STRONG ANALGESICS
«opiates» or «narcotic analgesics»
Morphine is the principle alkaloid (nitrogen containing organic compound)
10% of raw opium.
Codeine is 0.5% raw opium.
Heroin is synthesised by changing two –OH groups on morphine to two ester
(CH3COO-) groups.
Heroin is therfore semi-synthetic.
QUESTION
Look at structures of heroin, codeine and morphine at top of page 414. What
functional groups do they have ? How do they differ ?
ADVANTAGES AND DISADVANTAGES OF OPIATES
Use page 414 to take notes on….
Pharmacological effects
Medical uses
Psychological effects
Tolerance and dependence
QUESTIONS
4, 5 and 6 on page 434.