Infectious Diseases - Medicines

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  • Infectious Diseases: Medicines
  • Chemicals vs pathogens
  • Antibiotic resistance
  • Developing medicines
  • Different types of medicines
  • Quiz

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Developing medicines

To develop a new medicine it is important to understand how the human body works and how it is affected by a particular disease. A successful medicine treats hundreds of thousands or even millions of patients. It also makes money for the pharmaceutical company which in turn enables them to carry out research into more new medicines to treat more diseases. For any medicine to be successful it must be:

  • Effective
    it must prevent or cure the disease it is aimed at, or relieve the symptoms for the patient.
  • Safe
    it is very important that a medicine cures a problem without causing unacceptable side effects.
  • Stable
    it is important that the chemicals in the medicine can be used under normal conditions and be stored for some time.
  • Successfully absorbed and excreted by our bodies
    however good a medicine might be in theory, it is no use unless it can reach its target and then be removed from the body once it has done its work.

Research into a new medicine has to make sure that all these conditions are met. This is why it takes a very long time – up to 12 years – and a great deal of money – up to around £550 million – to bring a new medicine into the doctor's surgery.

Steps in developing a medicine

Ideas developed, disease targeted
Search for possible therapeutic compounds - this includes computer design of molecules and the screening of thousands of molecules which are already known or have been found in microorganisms, animals or plants
Cinchona tree

Cinchona tree – The bitter chemical made by the cinchona tree to protect itself from damage by pathogens became known as quinine and for many years it was the only effective treatment for malaria

yew tree

Yew tree – a chemical first found in the leaves of the yew tree has led to tamoxifen, one of the best known drugs in the battle against breast cancer.

Cone shell

Cone shell – Cone shells make a venom which they use to kill their prey, but some of the chemicals from the venom are being developed as effective pain killers.

Potential compounds synthesised in the lab
In vitro screening – testing the potential medicines on cell cultures, tissue cultures and isolated whole organs
Animal testing – the small number of molecules which have made it through the first stages are now tested on animals for more information about their likely safety and effectiveness.
Animal testing continues looking at the effect of longer term exposure to the medicine
Clinical testing on humans begins with phase I trials on a small number of healthy volunteers to start investigating the safety of the medicine in people.
Human phase II trials run with a small number of patients suffering from the target disease to decide the best dose to use, check it is safe and to start to investigate how well it works. Phase III trials continue this with a larger number of patients
If the scientists feel the medicine has passed all the trials, the company sends all the data to the international regulating bodies. If they are satisfied with the research the medicine will be granted a licence and can be prescribed by doctors for their patients to treat certain diseases
Once the medicine is on the market phase IV trials continue – the efficacy and safety of the medicine is monitored all the time the medicine is used. These long term trials mean that any unexpected side effects which only develop after the drug has been used for a long time, or which only affect a small group of people with a rare genetic makeup, can be picked up and dealt with.

Different types of clinical trials

When new medical treatments are being tested there are a number of ways the trials can be run. These include:

  • Randomised trials
    most drug trials are randomised after phase II. This means that patients are selected at random to get the experimental treatment or a comparator. The comparator may be a harmless pill with no action (a placebo) or the best available current treatment.
  • Open label trials
    both the researcher and the patient know what drug they are being given. Sometimes this is inevitable if, for example, you are comparing a medical treatment with physiotherapy or exercise.

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  • Blind trials
    the researcher knows if the patient is being given a trial drug or a placebo, but the patient does not – they are blind. The problem with this is that the researcher may give unconscious clues to the patient about whether they are getting the new treatment or not.
  • Double blind trial
    neither the researcher nor the patient know if the patient is being given the trial drug or not. Only a third person who is not involved in the research process has that information. This means that there is no chance of the researcher influencing the patient, consciously or not.
Medicine that acts against bacterial infections. Penicillin is an example of an antibiotic.
Protein that is produced by lymphocytes (white blood cells) and that attaches to a specific antigen.
Molecule on the surface of a pathogen that identifies it as a foreign invader to the immune system.
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus.
The use of biological organisms or enzymes to create, break down or transform a material
To cut apart, or separate, tissue especially for anatomical study.
Exponential growth
If something is growing exponentially the larger the quantity gets, the faster it grows
Micro-organism that can grow in long tubes called hyphae or as single cells. Fungi have a nucleus, cytoplasm and a cell wall.
Herd immunity
If a high percentage of a population is immune to a disease the disease cannot be passed on because it cannot find new hosts.
Infection caused by the human immunodeficiency virus (HIV). It attacks and destroys the immune system.
Hybridoma cells are formed by fusing a specific antibody-producing cell with a type of cancer cell that grows well in tissue culture
Immune system
The body's natural defence mechanism against infectious diseases.
A process which gives immune resistance to a particular disease. The human or animal is exposed to a harmless antigen in order to raise antibodies and provide an immune memory.
A type of white blood cell that make antibodies to fight off infections.
A type of white blood cell that consumes dead pathogens that have been killed by antibodies.
Organism that feeds off another living host and causes it some damage. An example of a parasite is a tapeworm that lives in the digestive system of a host organism.
A micro-organism that causes disease.
Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.
A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.
Protozoa are one-celled animals
A spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavourable conditions.
A poisonous or toxic substance - produced by pathogens.
A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.
Medicine that contains a dead or weakened pathogen. It stimulates the immune system so that the vaccinated person has an immunity against that particular disease.
The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell.
How well the drug works