Medicines and drugs Analgesics

What is an analgesic? How do you feel pain? What does “tolerance physical” mean? What does “physical dependence” mean in this context?

Analgesics – reduce pain

Mild analgesics – act at source 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 stimulate the pain receptors that send pain impulses to the brain. Prostaglandins also cause pain, swelling (=inflammation) or fever.

Strong analgesics (opiods) – act in brain or CNS Strong analgesics such as morphine and diamorphine (heroin) work by temporarily bonding to receptor sites (opiod receptors)to pain impulses in the brain or other parts of the central nervous system such as the spinal cord. This prevents the reception 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 and act in the brain or CNS Consider the relative value of these two approaches to pain management.

Structures of analgesics aspirin paracetamol benzene ring ester carboxylic acid benzene ring hydroxyl amide carbonyl

Structure of analgesics ibuprofen benzene ring carboxylic acid

A derivative = a new compound from changing another compound 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

Strong analgesics morphine diamorphine/heroin codeine benzene ring hydroxyl /alcohol (2) ether double bond tertiary amine ester (2) hydroxyl ether (2)

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 (an opiod). Heroin’s structure is only slightly different from morphine. Both the hydroxyl 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.

aspirin advantage 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 (1) euphoria, lack of self-control even dangerous behaviour kidney failure. 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 addiction or physical dependence which leads to withdrawal symptoms when drug is not taken e.g. restlessness, sweating, fever, cramping, …

Morphine - disadvantages 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.