Presented by: Manon Loustaunau

What are they?
Analgesics are pain-killers (think of the etymology of the word; Greek an "not" + algos "pain"). In order to be effective they must somehow intercept or block the pathways between the site of injury (pain receptors) and the perception of the pain in the brain.
Some common, mild, and frequently used analgesics
Some common, mild, and frequently used analgesics

Prostaglandins are the chemicals that stimulate the pain receptors at the site of injury and in the brain. They are released from cells damaged by thermal, mechanical, or chemical energy. Once the prostaglandins are released from the site of injury (the damaged cells), they cause an inflammatory response by dilating the blood vessels near the injury so that blood can flow to the injury quickly (to congeal and seal the wound, and bring white blood cells to fight bacteria and whatever else may have entered the body at the site of injury). This dilation of blood vessels is what causes swelling, which in turn can cause more pain because of increased pressure. Prostaglandins also affect the temperature regulation of the body which can lead to a fever. When the body raises its internal temperature (a fever) it is attempting to kill bacteria with heat as well as with white blood cells.

What are the two types of analgesics?
Analgesics can be split into two different categories, mild analgesics, and strong analgesics. Mild analgesics can be bought over the counter at drugstores to alleviate the pain of things like headaches, soreness, or mild injuries, or even reduce fever. Strong analgesics, on the other hand, can be illegal (heroin) because they are almost immediately addicting and so therefore very dangerous. Some strong analgesics are prescribed by doctors and used in hospitals (morphine) to relieve the suffering of patients, especially after an operation or breaking a bone.

Mild analgesics: aspirin, paracetamol (acetaminophen), ibuprofen
They work by preventing the stimulation of the nerve endings at the site of pain, essentially stopping the sensation of pain from being transmitted to the brain at the site of injury. This is done by preventing the release of prostaglandins from the damaged cells, so inflammation and fever are alleviated as well as pain. They are non-narcotic drugs because the drugs do not affect the functioning of the brain.

Strong analgesics: heroin, morphine, codeine
They work by binding to opiod receptors, the cells in the brain that transmit pain, and so block the transmission of pain, and so altering the perception of pain. Because they alter function in the brain, the perception of pain, strong analgesics are narcotics. They are the most effective painkillers, but may cause drowsiness or changes in mood or behavior. These drugs are also known as "opiates" because they derive from opium, from the poppy plant.They are also highly addictive and dangerous. Once addicted, withdrawal symptoms occur when the drug is not used, including cold sweats, anxiety, and diarrhea.

Salix Alba
Salix Alba

Aspirin comes from the bark of Salix alba, or a willow tree. The part of this bark that is effective as an analgesic and antipyretic (reduces fevers) is salicylic acid (2-hydroxybenzoic acid). Salicylic acid became widely used in the 1870s, but its side effects include irritation of the stomach, esophagus, and mouth. The ethanoate ester of salicylic acid was developed in 1899 by the German company Bayer. Modern aspirin still has side effects, most commonly bleeding of the stomach lining. Some people are violently allergic to it, causing them to suffer from bronchial asthma. An overdose of aspirin causes acidosis because the blood's pH is lowered.

Salicylic Acid
Salicylic Acid

(Functional groups: carboxylic acid, alcohol)

Children under 12 who take aspirin can develop Reye's disease, a liver and brain disorder that is potentially fatal. Various coatings are put on aspirin which can delay when the body processes the aspirin; some coatings delay the activity of the aspirin until it reaches the small intestine, which can reduce some of the side effects.
Structural diagram of Aspirin
Structural diagram of Aspirin

(Functional groups: carboxylic acid, ester)

Aspirin works by preventing the prostaglandin synthase enzyme from forming at the injury. This relieves pain because the enzyme is responsible for prostaglandins which cause fever, swelling, and the transmission of pain from the injury to the brain.

Besides being used as a mild painkiller, aspirin is an anti-inflammatory (because prostaglandins cause swelling around an injury) and thus is taken for arthritis; aspirin prevents blood clotting and so is taken to prevent strokes or recurring heart attacks; and recently aspirin is thought to prevent prostate cancer.

Paracetamol (Acetaminophen)
Because of the potentially serious side effects of Aspirin, Paracetamol (Acetaminophen) is often preferred as a mild painkiller. There are still serious but rare side effects, causing kidney damage or leading to a blood diseases. An overdose, even if not deadly, can permanently damage the liver and kidneys. However, when used correctly it is one of the safest analgesics.
external image Paracetamol-diagram.png
(Functional groups: alcohol, amide)

Paracetamol, like aspirin blocks the production of prostaglandins at the site of injury. However, it is ineffective in reducing inflammation or swelling at the site of injury.

Ibuprofen is a non-steroidal anti-inflammatory drug (NSAID). It has many of the side effects of aspirin, with the exception of stomach problems. An overdose can cause kidney problems, but it has a wide range of safe usage, and is effective even in low doses.
Structural diagram of Ibuprofen
Structural diagram of Ibuprofen

(Functional groups: alkyl, carboxylic acid)

The poppy plant, from which opium originates
The poppy plant, from which opium originates

Codeine, a natural (non-synthetic) drug is used in some cough medications and to treat diarrhea. Sometimes it is given in combination with a non-narcotic analgesic, like Ibuprofen.
Structural diagram of codeine

(Functional groups: benzene ring, alkene, alcohol, tertiary amine, ether)

Morphine is addictive and so must be strictly regulated. It is used to treat severe pain, like with terminal cancer.
Structural diagram of morphine

(Functional groups: benzene ring, ether, alkene, alcohol, tertiary amine)

Heroin is a semi-synthetic drug formed when -OH groups on morphine are altered to an ester functional group (CH3COO-) through a diesterification reaction. It is only legal medically in Britain and Belgium because it is very addictive and very quickly one's tolerance increases. It is used to treat severe pain; it is rapidly acting, producing a euphoric high. It is more lipid-soluble so it can cross the blood-brain barrier very quickly, and so its effects come soon after it is administered. Dependence on the drug leads to withdrawal symptoms. It is associated with HIV-AIDS because drugs user often share needles for injection (dirty needles).
Structural diagram of Heroin
Structural diagram of Heroin

(Functional groups: benzene ring, ether, alkene, ester-ethanoate, tertiary amine)

Methadone works like an analgesic, but unlike the other narcotic strong analgesics it does not create a feeling of euphoria, which is what is craved by addicts. It is used when trying to wean heroin addicts off the drugs, because it gives the chemical the body craves without a psychological benefit, and so lessen the addiction and so the withdrawal. It has amine and ketone functional groups.

Narcotic drugs have a large range of side effects (other than the intended effect of relieving pain).
Short term:
  • sedation, stupor, euphoria
  • impaired coordination
  • temporary impotence
  • reduced anxiety and fear
  • death if overdosed
Long term:
  • malnutrition, changed or loss of appetite
  • if used illegally, risk of AIDS or hepatitis from shared needles
  • sterility
  • addiction, withdrawal

Some completely synthetic opiates, like demerol (meperidine), methadone (dolophine), and fentanyl (sublimaze), have the same effects of opiates, but are "cooked" in laboratories. Demerol is a derivative of morphine. Methadone is used to treat the withdrawal of heroin addicts.

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Brown, Catrin and Ford, Mike. Higher Level Chemistry. Pearson Baccalaureate: Edinburough Gate, 2009.
Neuss, Geoffrey. IB Study Guide: Chemistry for the IB Diploma. Oxford University Press: Oxford, 2007.
Green, John and Damji, Sadru. Chemistry, 3rd Edition. Ibid Press: Victoria, 2007.