D.3 Analgesics
D.3.1
Pain
Describe and explain the different ways that analgesics prevent pain
→ an unpleasant sensory or emotional experience associated with actual or potential tissue damage.
Pain receptors → nerves in our bodies that transmit pain signals along nerves, to the spinal cord and brain for interpretation.
The skin has more pain receptors than the GI tract so it is harder to pinpoint the precise location of a stomach ache than a
bruise, cut, or burn.
Pain receptors are attached to two main types of nerves
 one that relays messages quickly sharp, acute pain
 the other that relays messages slowly  dull, throbbing pain
The spinal cord receives the message, and then sends it to a brain structure called the thalamus.
The thalamus also contributes to mood and arousal, which helps to explain why our interpretation of pain partly depends
on our state of mind. The pain message is then delivered to the brain's cerebral cortex. Interestingly, some people who
have injuries to areas of their cerebral cortex still experience pain, but don't care about it that much.
Analgesics are medicines that relieve pain.
Four classes of analgesics:
1. mild analgesics – acetaminophen and NSAIDs
2. strong analgesics - narcotics (opioids)
3. local anesthetics (licocaine)  block nerve conduction an decrease blood supply
4. general anesthetics (chloroform, ether, N2O)  induce unconsciousness
Analgesics relieve symptoms not the cause of the pain.
B.3.2
Describe the use of derivatives of salicylic acid as mild analgesics and compare
the advantages and disadvantages of using aspirin and paracetamol (acetaminophen)
Mild Analgesics
1. Acetaminophen
→ relieves pain by elevating the pain threshold; more pain needed before it is felt.
→ antipyretic
2. NSAIDs, non-steroidal anti-inflammatory drugs
 Corticol Steroids (Cortisone, Prednisone) – steroids used to reduce inflammation
 NSAIDs (ASA, ibuprofen) – reduce production of prostaglandins and the inflammatory response
 COX inhibitors – bind to cyclooxygenase enzyme to prevent creation of prostaglandins.
 Prostaglandins – chemicals, similar to hormones, which trigger physiological changes like increased temperature and
dilation of blood vessels.
 If prostaglandin production is blocked, fever and inflammation is reduced.
 Prostaglandins also help the stomach lining to resist gastric acid which is why aspirin can cause stomach irritation and
bleeding in some people
Antipyretic
→ reduces fever
Antipyretics affect the temperature-regulating centre of the brain (hypothalamus)
Antiplatelet agent = blood thinner  prevents abnormal blood clotting
Prostaglandins cause platelets to stick together to form clots
Table 1. A comparison of aspirin and paracetamol (acetominophen). Topic D.3.2.
Anti-pyretic
Anti-inflammatory
Pros
Best pain relief
Acetylsalicylic acid
√
√
Blood thiner
(ASA) Aspirin
Acecaminophen
Tylenol
√
No stomach irritation
Fewer interactions
Fewer side effects
Cons
Reye’s syndrome in children
Increases stomach bleeding
- worsened by alcohol
Potential damage to liver
Reduced pain relief
Same pain relief as ibuprofen
B.3.3
Compare the structures of morphine, codeine, and diamorphine (heroin, a semi-synthetic opiate).
Strong Analgesics - Narcotic analgesics (opioids) are all derived from opium.
 Natural Painkillers – endorphins and enkaphalins




bind to neuro-receptors of the brain
responsible for runner’s high, rugby high,
temporary loss of pain for severe injury
produced through acupunture and chiropractic adjustments
 Opioids − morphine, heroin, codeine, Demerol, Methadone
 alter pain messages by influencing brain chemistry
 strong pain relief of severe pain
 heroin is 6x stronger than morphine and 36x stronger than codeine
 ALL tend to be addictive
Narcotic = “sleep inducing”
Alkaloid → nitrogen-containing drug or medicine
Opium alkaloids
All have effects on the body similar to morphine
All have the same basic structure
 phenyl ring
 2 x 6-carbon rings, one has a double bond
 6-membered ring including a nitrogen attached to a methyl group
 5-membered ring with an oxygen
Each drug has different functional groups:
Morphine – two hydroxyl (-OH) groups
Codeine - hydroxyl (-OH) and methyl group attached to oxygen
Heroin – two acetyl (CH3COO) groups - diester
B.3.4
Discuss the advantages and disadvantages of using morphine and its derivatives as strong analgesics.
Table 2. Summary of the effects of narcotics
Usual short-term effects
sedation and stupor;
pain relief
euphoria
impaired functioning and coordination
temporary impotence
Typical long-term effects
loss of appetite
malnutrition and constipation
sterility
reduced tension, worry and fear
withdrawal, illness, loss of job, crime
reduced coughing reflex
diversion of energy and money
occasional death from overdose
risk of infection from shared needles (HIV, Hepatitis)