Antibiotics, Painkillers & Development of Drugs

Table of Contents
1. Antibiotics & Painkillers
2. Antibiotic Resistance
3. Discovering New Drugs
4. Testing New Drugs
5. Developing New Drugs
6. Solved Examples
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Antibiotics & Painkillers

• When treating a disease there are two types of medication that an individual can take:
  • Medicines that treat the cause of the disease - antibiotics
  • Medicines which treat the symptoms of the disease - eg. painkillers
• Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body
• The use of antibiotics has greatly reduced the deaths from infections in the last century
• Only certain antibiotics will work on certain diseases, however, so a doctor will prescribe different antibiotics depending on the type of infection (see Culturing Microorganisms)
• It is important that specific bacteria should be treated by specific antibiotics that are known to work against them
• Antibiotics work by stopping bacteria cellular processes such as the production of the cell wall - they affect processes usually only in bacteria so are not harmful to animal cells
  
  Penicillin was the first antibiotic to be discovered and is widely used, although resistance is a problem
• Antibiotics will not work against viruses, as viruses reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the body's tissues
• Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens (eg. ibuprofen can reduce pain and inflammation)

Antibiotic Resistance

• The use of antibiotics has increased exponentially since they were first introduced in the 1930s
• In that time they have saved millions of lives
  
  The introduction of antibiotics has had one of the largest impacts on global health, shown by this example in the USA
• However, since their discovery and widespread use, antibiotics have been overused and antibiotic resistance has developed in many different types of bacterial species
  • Bacteria, like all organisms, have random mutations in their DNA
  • One of these mutations may give them resistance to an antibiotic
  • If an organism is infected with bacteria and some of them have resistance, they are likely to survive treatment with antibiotic
  • The population of the resistant bacteria will increase
  • If the resistant strain is causing a serious infection then another antibiotic will be needed
  • A strain of Staphylococcus aureus has developed resistance to a powerful antibiotic methicillin, this is known as MRSA (Methicillin resistant Staphylococcus aureus)
  • MRSA can infect wounds and is difficult to treat without antibiotics
    
    Bacteria evolve rapidly as they reproduce quickly and acquire random mutations - some of which confer resistance

• To reduce the number of bacteria that are becoming resistant to antibiotics:
  • Doctors need to avoid the overuse of antibiotics, prescribing them only when needed - they may test the bacteria first to make sure that they prescribe the correct antibiotic
  • Antibiotics shouldn't be used in non-serious infections that the immune system will 'clear up'
  • Antibiotics shouldn't be used for viral infections
  • Patients need to finish the whole course of antibiotics so that all the bacteria are killed and none are left to mutate to resistant strains
  • Antibiotics use should be reduced in industries such as agriculture - controls are now in place to limit their use in farming

• Good hygiene practices such as handwashing and the use of hand sanitisers have reduced the rates of resistant strains of bacteria, such as MRSA, in hospitals
• The isolation of infected patients to prevent the spread of resistant strains, in particular in surgical wards where MRSA can infect surgical wounds

Discovering New Drugs

• Traditionally drugs were extracted from plants and microorganisms
• New drugs are being developed all the time by scientists at universities and drug companies around the world
• Lots of the medications that we use today are based on chemicals extracted from plants
  • The heart drug digitalis originates from foxgloves
  • The painkiller aspirin originates from willow
  • Penicillin was discovered by Alexander Fleming from the Penicillium mould
• Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant

Drugs from plants table

• Penicillin was first discovered by Alexander Flemming in 1928. He left some Petri dishes that had been contaminated with mould and found the bacteria would not grow near the mould
• He discovered that the mould (Penicillium notatum) was releasing a chemical (penicillin) that killed the bacteria surrounding it
• New drugs are now developed by the pharmaceutical industry. Many of these still have plants as their source

Testing New Drugs

• All new drugs need to be tested and trialled before they can be used in patients. They are tested for:
  • Toxicity - does it have harmful side effects?
  • Efficacy - does the drug work?
  • Dose - what dose is the lowest that can be used and still have an effect?
• The results of any testing are then peer-reviewed to make sure that the results are described accurately. The results would then be published in journals

Developing New Drugs

• Preclinical testing is done in a laboratory using cells, tissues and live animals
• Clinical trials use healthy volunteers and patients
• Very low doses of the drug are given at the start of the clinical trial
• If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug
• In double-blind trials, some patients are given a placebo

The 3 stages of drug development

• Preclinical Testing
  • The drug is tested on cells in the lab
  • Computer models may also be used to simulate the metabolic pathways that may be taken by the drug
  • Efficacy and toxicity are tested at this stage
• Whole organism testing
  • The drug is tested on animals to see the effect in a whole organism - all new medicines in the UK have to have tests on 2 different animals by law
  • Efficacy, toxicity and dosage are tested at this stage
• Clinical trials
  • The drug is tested on human volunteers first, generally with a very low dose then increased. This is to make sure it is safe in a body that is working normally
  • The next stage is to test on patients with the condition.
  • The patients are often split into two groups; one given the drug the other given a placebo. This is called a double-blind study - neither the doctor nor the patient knows if the patient is getting the placebo or the active drug
  • Once the drug is found to be safe then the lowest effective dose is tested at this stage

Future medications

• Pharmaceutical companies are always looking to find new medications these include:
  • Vaccinations to different diseases
  • Antibiotics that have a different action on the bacteria, so that bacteria are not resistant to them
  • Painkillers with fewer side effects
  • Antiviral drugs that don't damage the body's tissues
• Sources of these medications may be plants or microorganisms

Exam Tip: You should be able to describe the process of discovery and development of potential new medicines, including preclinical and clinical testing in the exam.

Solved Examples

Example 1: HIV/AIDS is what type of pathogen?

HIV/AIDS is a virus.

Example 2: Salmonella is what type of pathogen?

Salmonella is a bacterium.

Example 3: Rose black spot is what type of pathogen?

Rose black spot is a fungus.

Example 4: Malaria is caused by what type of pathogen?

Malaria is caused by a protist.

Example 5: What term describes an organism that transmits a disease?

A vector is an organism that transmits a disease.

Example 6: How is measles often transmitted?

Measles is often transmitted through the air. Escherichia coli is an example of a disease transmitted by uncooked food.

Example 7: In which foods is Salmonella more likely to be found?

Meat, eggs and poultry are more likely to contain Salmonella.

Example 8: Which of these does not prevent the spread of diseases?

Cancer screening does not prevent the spread of the disease. It makes early treatment more likely.

Example 9: Which of these is a non-specific defence against disease?

Skin is a non-specific defence against infection.

Example 10: Which of these do lymphocytes not produce?

Lymphocytes do not produce antigens. Antibodies are produced by lymphocytes after exposure to a pathogen.