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Body defences: 9. Introduction to drugs - medicines and their development and testing for treating diseases

Doc Brown's Biology exam study revision notes

Sub-index of notes: Our body's defence mechanisms against infections from pathogens, help from vaccines & drugs

(9a) Introduction to drugs - medicines for treating diseases

For more on drugs, solvents and alcohol see

 Keeping healthy - non-communicable diseases - risk factors

Drugs are substances that affect how the body works.

A drug can be defined as any substance taken into the body that modifies or affects chemical reactions in the body - which of course can be helpful and harmless, but also harmful, especially is use is abused.

Most drugs are proven safe medicines to use, but some are potentially dangerous if misused.

Many drugs can be bought directly from a pharmacy, but others can only be obtained from a doctors prescription.

The first thing you should appreciate is the difference between 'feeling better' and being 'cured'!

If you are injured, some of your sensory nerve endings send pain messages to the brain - an unpleasant experience.

Painkillers block these nerve impulses, reducing pain sensation and making you feel better.

Some painkillers were originally derived from plants e.g. an aspirin like molecule is found in willow bark and opiates are extracted from the poppy flower.

From these naturally occurring molecules, lots of synthetic derivatives have been developed like codeine.

Some drugs like aspirin or paracetamol relieve pain and reduce discomfort i.e. reduce the symptoms, but they do not counteract the disease you are suffering from e.g. a virus giving you a headache - but pain killers are better than nothing and enable to carry on with life with less discomfort while your body's immune system fights the infection.

Such drugs do NOT cure you because they do NOT kill the pathogen causing the disease in the first place.

Lots of other drugs such as cold remedies, decongestants, analgesic pain killers etc., cannot destroy e.g. the cold or flue virus but do make you feel a lot better and help you get a better night's sleep!

Other drugs e.g. the antibiotic penicillin do kill or inhibit the growth of certain bacterial infections by interfering with the pathogen's metabolism e.g. the biochemical processes that build bacterial cell walls.

(See section on healthy2defence-10.htm)

However, they are not a 'blanket cure', different types of bacteria require different types of antibiotic and the correct match is required to effect a cure.

Note that nothing is perfect in medicinal treatments!

Whether the drug is a painkiller, antibiotic, antiviral etc. people can suffer adverse effects e.g.

some people exhibit an allergic reaction to penicillin.

Some drugs are expensive and maybe need to be taken for a long time, without the outcome being wholly effective - doctors have to make some crucial judgements on what to prescribe.

Medical practitioners have to 'juggle' costs versus benefits, especially the more expensive the treatment.

There are also problems from the development of antibiotic-resistant bacteria like MRSA 'superbugs'

For more on drugs, solvents and alcohol see

Keeping healthy - non-communicable diseases - risk factors

(9b) Developing and testing new drugs and medicines

See also

Products of the Chemical & Pharmaceutical Industries & impact on us (GCSE chemistry

For more on drugs, solvents and alcohol see

Keeping healthy - non-communicable diseases - risk factors

It has been known for some time that plants produce a wide range of chemicals to defend themselves against attack from e.g. insect pests or pathogen microorganisms.

Historically, currently and in the future, these substances provide a basis for developing drugs to treat human diseases.

Even some of our current medications come from knowledge of plants giving us many traditional herbal recipes e.g.

(i) The painkiller aspirin was developed from chemicals in willow plants that reduce fever and reduce pain in childbirth.

(ii) Drugs like digitalis have developed from chemicals found in foxglove plants and are used to treat heart conditions.

Many antibiotics are made from growing microorganisms (first found by 'accident'!) e.g.

(i) The famous scientist Alexander Fleming noticed in some petri dishes used for investigating bacteria, a mould had grown, but the area around the mould was free of bacteria.

He realised that the mould (in this case Penicillium notatum), was producing a chemical that killed the bacteria.

This chemical was extracted and named penicillin, and proved to be a very effective antibiotic in killing various bacterial infections.

(ii) These days pharmaceutical companies grow fungi and other microbes on a large scale and extract the antibiotic molecules in the laboratory.


Decisions - scientific and commercial!

Any new drug must be targeted at some specific medical condition where there is need - otherwise it would not make commercial sense to develop a new pharmaceutical product.

From a scientific point of view, many drugs are designed to inhibit part of the chemistry of a disease e.g. targeting a gene or a protein like an enzyme.

The target might be blocking the action of an enzyme or a gene with a chemical agent (drug) you can interfere with the development of a disease e.g. the anti-cancer drugs used in chemotherapy treatments to reduce the growth of tumour cells or kill them.

Studies of the genomes and resulting proteins in both plants and animals are proving useful to identify 'targets'.

You then have to find a chemical that will have an effect on the target.

There are databases of chemicals that have been screened by advanced analytical techniques which can be consulted for likely effectiveness.

The screening might not initially indicate the best molecule to 'hit the target' in a biochemical sense, but, it may provide a useful starter molecule.

You can then modify the starter molecule to produce a variety of derivative molecules, one of which might provide a more effective treatment. The derivative molecules can be quite similar, but it is a sort of 'fine tuning' of their molecular structure to increase the drug's effectiveness.


Today drugs are manufactured on a huge scale in the pharmaceutical industry.

Chemists can synthesis molecules based on naturally found organic compounds from plants and also lots of molecules that have never existed in nature until synthesised in a modern chemical laboratory.

Historically, most effective drugs were discovered by accident e.g. somebody by chance notices some effect of a chemical which might have a medical application.

However, these days, research is very systematic and we have an extensive database of knowledge about the structure and properties of molecules AND how diseases work.

Some drugs have been successfully designed by computer software that can construct and display molecular structure e.g. design a molecule with a shape to fit into the active site of an enzyme to inhibit its action.

See also Products of the Chemical & Pharmaceutical Industries & impact on us (GCSE chemistry)

(9c) Developing a new drug - a lengthy and costly process!

The drugs developed and produced by the pharmaceutical industry are often very costly in the making for several reasons

You have to carry out a lot of research and development to find a suitable compound that performs an effective medical treatment for some condition e.g. to reduce blood pressure, kill cancer cells, slow down the development of dementia etc.

The compound must be tested, often modified and retested.

All new potentially useful drugs must be fully tested in trials including animal trials (controversial) and human trials and this all takes time and money.

Until a drug has fully passed all safety and effectiveness tests it cannot be marketed and sold to medical institutions from hospitals to high street pharmacies etc. The manufacturer must prove that any pharmaceutical product like a drug does meet all legal requirements that it does actually work and is safe to use.

The stages in the testing of a new drug-medicine is summarised below:

Stage 1 Preclinical testing (non-living animal testing):

Computer models can be used initially to simulate a human's responses to a drug and can identify possible effective drugs, but cannot possibly be as accurate as actually using cell tissue cultures or live animals.

In preclinical testing the drugs are tested on cultured human tissue cells in the laboratory.

However, these procedures cannot be used to test drugs that affect a complex body system.

e.g. a drug for controlling blood pressure must be tested on a whole live animal with its complete intact circulatory system.

Stage 2 Preclinical testing (live animal testing):

If the stage 1 tests prove satisfactory, and no potential harmful effects are detected, you can then move onto testing the drug on live animals.

This is to see whether the drug works and producing the desired medical effect (this is known as testing the efficacy of the drug).

You are also looking for potential harmful side effects, including toxicity, from using the new drug.

You are also investigating the appropriate dosage in terms of concentration/amount and frequency of administering the drug.

According to UK law, any new drug must be tested on two different live mammals, but there are objections to this on several grounds:

(i) Many people object on the grounds it is cruel and unethical to use animals in tests, but others think drug safety should override these considerations i.e. avoid the use of a potentially dangerous drug.

(ii) Animals used in testing drugs are not quite the same as humans. Could their biological differences give us false results in terms of the efficacy of the drug when used on humans?

Stage 3 Clinical testing on humans:

If the drug has passed all the preclinical tests, you can then test it on human volunteers in what is called a clinical trial - which is just as complicated as any research laboratory testing.

Initially, the drug is tested on healthy volunteers - this is the only way to find out if there are any harmful side effects on a healthy body working normally.

Initially it is unsuitable to test the drug on sick people who are likely to be more vulnerable to side effects.

At first very low doses of the drug are administered to healthy people and then the dose is gradually increased and the participants medical state closely monitored.

If the results of the tests on healthy individuals are good and meet any health and safety criteria, the drug can then be tested on patients suffering from the illness-disease the drug is designed to combat.

From these tests the optimum dose is found - that is the dose that is most effective with the fewest side effects.

The safety and effectiveness of the new drug must be thoroughly checked out.

This takes some time, human drug trials may last for months or even years.

Sometimes this is due to the long term progression of a disease e.g. cancer and the time taken for the treatment to be shown to be effective.

It might also be a long time before the symptoms of side effects show up.

We now get into the practice of how to get statistically valid results from real patients.

To test the effectiveness of a drug a group of patients are randomly selected into two groups.

One group is given the new trial drug and the other group, the control group, a placebo - a substance that looks like the drug being tested, but has no effect - it can be just a sugar pill.

The control group (placebo group) of a clinical trial should be similar to the people actually being treated with the trial drug e.g. of similar age and gender.

Using a placebo ensures the doctors can see the real difference the drug is having on the patient's condition. This also allows for where the patient does expect an improvement in their medical condition and might actually feel better - even though unknowingly, nothing has been taken to improve the medical situation!

In some trials on seriously ill patients, placebos are not used - it would be unethical not to allow all patients the same chance of benefiting from the new drug.

In other trials doctors might test new drugs against the best existing treatment instead of testing against a placebo.

Note that that clinical trials must be blind, meaning, the patient in the trial doesn't know whether they are getting the new drug or a placebo, but the doctors do know who has the trialled drug or the placebo.

Sometimes the clinical trials are double-blind where neither the patients nor the doctors know who has the drug or placebo until all the results have been gathered and analysed. This ensures the doctors administering, monitoring and analysing the drug trial are not subconsciously influenced by their knowledge of the patients.

Before any drug is approved for use in our healthcare systems, the results of drug testing trials must be peer reviewed by other equally qualified medical practitioners.

This is essential to avoid false or biased claims of the new drug's performance in real patients.

Drug trials can also 'open-label' where the doctor and the patient are aware of who is receiving the drug. This can be used when comparing the effectiveness of two similar drugs being trialled.

Peer reviewers must check the validity of the drug trial e.g. has it been correctly designed and rigorously carried out to the highest scientific standards.

Finally, the drug can only be approved for patients of the general public after permission is granted by the appropriate medical agency if all health and safety criteria are met. The rules are strict to ensure the drugs are as effective and safe to use as possible.

Thalidomide: A tragic classic case of insufficient testing

Thalidomide is a drug that was developed as a sleeping pill in the 1950s and was tested for its effectiveness, but only as a sleeping pill.

Later it was also found to be effective in relieving morning sickness in pregnant women.

However, the drug thalidomide had not been tested for use in pregnant women, in particular it was not tested for relieving morning sickness.

Also, it was not known that the drug could pass through the placenta and into the foetus (fetus), where unfortunately, it caused abnormal limb development.

Thousands of babies were affected and about half survived with missing limbs or malformed limbs.

Around 10 000 babies were affected and only half of them survived.

It was only after many babies born to mothers who took the drug were born with severe limb abnormalities that the drug was then banned for this use.

As a result, drug testing has become much more rigorous in an attempt to reduce the incidence of serious side-effects from newly developed drugs..

More recently, thalidomide has been used successfully in the treatment of leprosy and other diseases including some cancers.

Learning objectives for this section on ?

Know that drugs for medical applications are continuously being developed, but need thorough testing of their safety and effectiveness before their use is allowed in treating diseases

Know that trials of new drugs will involve testing with cell cultures, animals and finally patients.

Know that thalidomide was tragic classic case of inadequate testing of a pharmaceutical product.



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