Option D3: Analgesics

D.3.1 Describe and explain the different ways that analgesics prevent pain

Mild analgesics, including aspirin and non-steroidal anti-inflammatory drugs (NSAID) such as ibuprofen, act by preventing stimulation of the nerve endings at the sit of the pain. They inhibit the release of prostaglandins from the site of injury and so give relief to inflammation and fever as well as to pain. (Paracetamol is an exception as it inhibits prostaglandin release int he brain rather than at the sit of the injury.) These analgesics do not interfere with the functioning of the brain, they are also known as non-narcotics.

Strong analgesics include the drugs related to morphine, known as the opioids. This refers to their ability to bind to so-called opioid receptors in the brain, which then blocks the transmission of pain signals between brain cells and so alters the perception of pain. Because these analgesics act on the brain, they may cause drowsiness and possible changes in behaviour and modd, so are also known as narcotics. They are the most effective pain killers for severve pain, but owing to their side-effects and potential problems with dependence, their usage must be monitored through medical supervision.

D.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)

Salicylic acid proved to be effective in treating pain but it tastes awful and caused the patient to vomit. The Bayer company in Germany made an Ester derivative of salicyclic acid, while still effective as an analgesic. It was named aspirin, which produces a similar compound.

Aspirin is widely used in the treatment of headache, toothache and sore throat. Also, because it is effective in reducing fever (an antipyretic) and inflammation, it is used to provide relief from rheumatic pain arthritis. Aspirin reduces the ability of the blood to clot and this makes it useful in the treatment of patients at risk from heart attacks and strokes. Negative side-effects include irritation and even ulceration of the stomach and duodenum, possibly leading to bleeding. This effect can be more acute when it is taken with ethanol in alcoholic drinks. A large number of people, especially those prone to asthma, are also allergic to aspirin, so it must be used with caution. It is not recommended for children under 12 because its use has been linked to Reye's syndrome, a rare and potentially fatal liver and brain disorder.

Paracetamol is much younger drug than aspirin, having been marketed only since 1953. Paracetamol is different from other mild analgesics as it is thought to act by reducing the production of prostaglandins in the brain, but does not affect prostaglandin production in the rest of the body. This means that it is not effective in reducing inflammation. It is one of the safest of all analgesics when taken correctly. It does not usually irritate the stomach and allergic reactions are rare. However, an overdose or chronic use of paracetamol can cause severe and possibly fatal damage to kidneys, liver and brain.

D.3.3 Compare the structures of morphine, codeine and diamorphine (heroin, a semi-synthetic opiatic)

The narcotic drugs derived from opium are primarily morphine and its derivatives. We will consider three of these here: codeine, morphine and diamorphine, known as heroin. These are powerful analgesics, acting on the central nervous system to block the perception of pain.

Has benzene ring, 2 ethers, alkene, alcohol and tertiary amine functional groups. It is found in raw opium (0.5%).

Has benzene ring, ether, alkene, 2 alcohol and tertiary amine functional groups. It is found in raw opium (10%).

Has benzene ring, ether, alkene, 2 ester -ethanoate and a tertiary amine. It is found in opium but usually obtained by reaction of morphine, so is known as a semi-synthetic drug.


D.3.4 Discuss the advantages and disadvantages of using morphine and its derivatives as strong analgesics

Codeine

Its therapeutic uses sometimes used in a preparation witha non-narcotic drug such as aspirin or paracetamol in the second stage of the pain management ladder. It is also used in cough medicine and in the short-term treatment of diarrhoea.

Morphine

It therapeutic uses are used in the management of severe pain, such as in advanced cancer. It also can be habit forming and can lead to dependence, so use must be regulated by a medical professional.

Diamorphine

Its therapeutic uses are used medically only in a few countries legally (Britain and Belgium) for the relief of severe pain. It has the most rapidly acting and is the most abused narcotic. It initially produces euphoric effects, but very high petential for causing addiction and increasing tolerance. Dependence leads to withdrawal symptoms and many associated problems.