Answers to questions on Pharmaceutical products & drug action

1. Drugs can be injected under the skin (subcutaneous), into the muscle (intramuscular) and directly into a vein (intravenous). Injecting directly into a vein produces the quickest reaction that affects the whole body. Subcutaneous injections are used for topical effects such as for local anaesthetics.

Three other ways in which drugs can be injected are by mouth (orally), by inhalation and through the IB Docs (2) Teams (rectally). Drugs can also be applied topically on the surface of the skin.

2. The ED₅₀ is the dosage of the drug required to bring about a noticeable effect in fifty percent of the population. The LD₅₀ is the dosage required to bring about the death of 50% of the animal population to whom the drug has been administered.

Determining the LD₅₀ causes the ethical problem that animals must be killed in the interests of scientific research. There is also the problem that different animals react to drugs in different ways so there is no easy way to extrapolate the finding to human beings.

3. Side effects are the unwanted effects of a drug. They may be mild or severe and possibly even life-threatening and can vary from person to person. If aspirin is taken as an analgesic (pain killer) then common side effects include bleeding of the stomach and also thinning of the blood. However this second ‘side effect’ of aspirin can alter the reason why aspirin is taken and become the main effect when aspirin is prescribed for people at risk of heart problems or a stroke to lower the risk of blood clotting. Similarly one of the side effects of morphine, which is a strong pain killer, is constipation and sometimes morphine is prescribed for someone suffering from diarrhoea. Other unwanted side-effects of morphine can include headaches, nausea and dizziness as well as the possibility of addiction.

4. Morphine acts directly on the central nervous system. Morphine itself is only sparingly soluble in water. Because they are far more polar, ionic salts of morphine are considerable more soluble in water so enable the morphine to be carried around the body more effectively.

5. Thalidomide was introduced as a sedative in the 1950s. It was found to be an effective anti-emetic and was given to pregnant women to prevent morning sickness. At that time no real research had been done on the possibility of drugs crossing the placental barrier to the foetus. The drug was produced by a German company called Grünenthal and by the Distillers Company in the UK. Although their own research showed some problems they did not initially withdraw the drug even when there were reports that babies were being born with severely deformed limbs. This was because they were making large profits from its sales. The drug was eventually withdrawn in the early 1960s after more than 10,000 babies had been born with the deformities. In 1968 a successful court case led to the Distillers Company paying out a large sum of money in compensation. Since the thalidomide affair there has been a much stricter policy of regulating and licensing new drugs.

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