Medicines and drugsAnalgesics

What is an analgesic?

How do you feel pain?

What does “physical dependence” mean?

What does ‘tolerance’ mean in this context?

Analgesics – reduce pain

Mild analgesics

Mild analgesics, such as aspirin and paracetamol, function by stopping the transmission of pain from source to brain as they intercept the pain stimulus at the source.

They do this by interfering with the production of substances, such as prostaglandins, that are produced by injured tissues and that cause pain, swelling or fever.

Strong analgesics - opioids

Strong analgesics such as morphine and diamorphine (heroin) work by temporarily bonding to receptor sites to pain impulses in the brain or other parts of the central nervous system such as the spinal cord.

This prevents the transmission of pain impulses i.e. blocking the signal without depressing the central nervous system.

Mild or strong?

Mild analgesics eliminate pain at source

Strong analgesics alter our ability to perceive pain

Consider the relative value of these two approaches to pain management

Structures of analgesics

aspirin

benzene

ester

carboxylic acid

paracetamol

benzene

hydroxyl

amide

carbonyl

Structure of analgesics

ibuprofen benzene carboxylic acid

Aspirin – a derivative

salicylic acid….

into aspirin

A derivative = a new compound from

changing another compound

To convert salicylic acid (2-

hydroxybenzoic acid) into aspirin the

hydrogen atom of the OH group is replaced by a COCH3 group to

form an ester functional group which made the compound less irritating to the

stomach and easier to take.

morphine

morphine

Strong analgesics

morphine diamorphine/heroin

codeine

• benzene hydroxyl

/alcohol (2) ether double bond tertiary amine

benzene ester (2) ether double bond tertiary amine

benzene hydroxyl ether (2) double bond tertiary amine

heroin- another derivative

Diamorphine or heroin is a derivative of morphine or a semi-synthetic opiate. An opiate is a chemical which has the same physiological effect as morphine.

Heroin’s structure is only slightly different from morphine. Both the hydroxyl or alcohol groups in morphine have been replaced with ester groups. This is achieved by reacting the morphine with ethanoic acid; as a result an esterification occurs during which also water is produced.

Also codeine is a morphine derivative.

aspirinadvantage disadvantage

reduces fever more effectively – antipyretic (=drug which reduces fever)

also useful in preventing the recurrence of heart attacks and strokes and also thins the blood (beneficial side-effects) and reduces blood clotting

also anti-inflammatory – reduces inflammation or swelling

ulceration stomach bleeding due

to its acidic properties allergic reactions Reye’s syndrome in

children (a potentially fatal liver and brain disorder) so not so suitable for children

paracetamol

advantage disadvantage reduces fever –

antipyretic

very safe in the correct dose as it does not upset the stomach or cause bleeding

suitable for children

can, in rare cases, cause blood disorders and kidney damage.

easier to overdose and overdosage can lead to serious liver damage, brain damage and even death.

not a good anti-inflammatory

Using morphine - advantages

strong analgesics and therefore can relieve extreme pain

wide therapeutic window

relieves anxiety

induces relaxation

can be administered intravenously which results in faster distribution of drug

Morphine - disadvantages euphoria, lack of self-control even dangerous behaviour

kidney failure.

addiction or physical dependence which leads to withdrawal symptoms when drug is not taken e.g. restlessness, sweating, fever, cramping, …

tolerance can become an issue with this type of drug as more of the drug needs to be taken to achieve the same effect; in order to achieve the desired effect heroin users may take doses which exceed the lethal dose

Social: heroin users are more likely to commit crimes to pay for

gradually increasing doses of the drug loss of job diversion of energy and money when administered intravenously can lead to transmission of

dangerous infections e.g. AIDS.