drugs from plants and drug testing

how are plants useful for us in medicine?

some have antimicrobial properties

how to investigate the antimicrobial properties of plants

1. prepare an agar plate that contains nutrients for bacteria to grow

2. use a sterile pipette to transfer bacteria grown in a nutrient broth to the agar plate

3. use a sterile plastic spreader to spread a thin layer of bacterial solution evenly across the surface of the agar plate

4. cover with a lid while you prepare other things (aseptic techniques)

5. make extracts of plants - dry and grind the plant and soak in ethanol then filter out the solid pieces

6. use sterile forceps to dip equally sized sterile absorbent paper into the plant extracts

7. make a control disc soaked only in ethanol

8. tape the lid shut

9. invert and incubate at 25 celcius for 24-48 hours (prevents the grown of unwanted human pathogens (pathogens that can make us sick)

10. measure the zone of inhibition where bacteria wasn’t able to grow

11. repeat and average

why do we use ethanol to make the plant extracts?

antimicrobial substances are soluble in ethanol

what control variables should we consider when carrying out the antimicrobial plant extract practical?

• soak the ground plant in ethanol for the same amount of time

• put the same mass of ground plant in the ethanol

• let the paper discs soak up the liquid for the same amount of time

• make a control disc with only ethanol to see the effects due to ethanol and take this into account

what does bacterial growth require?

• oxygen for aerobic respiring bacteria

• nutrients

• the right temperature and ph - affects enzyme activity and metabolic processes

what aseptic techniques can we use?

• close windows and doors prevents drafts of air pushing unwanted microbes into the practical

• disinfect surfaces minimise contamination

• sterile equipment and discard after - minimise contamination

• work near bunsen flame to kill microbes in air and draw them away from agar plate

• flame the glass containers - causes air to move out the container

how was drug testing different earlier?

william withering example

• discovered foxgloves could be used to treat dropsy

• foxgloves contained digitalis

• foxgloves are poisonous

• trial and error with different versions of the same digitalis soup with different concentrations

how is modern drug testing different now?

• drug modelled on computers (models potential effects)

• tested on human tissues and cells in a lab

• tested on live animals

clinal trials

• phase 1 - test on small group of healthy people to find the safe dosage and side effects (how the body reacts)

• phase 2 - test on a larger group of people with the disease to test the effectiveness of the drug

• phase 3 - tests on hundreds or thousands to compare it to existing treatments

why do we test on large numbers of people to test a drug?

to make results more reliable

use of placebos in clinical testing

when testing on people with the disease in phase 2, half are given the drug, half are given placebos (an inactive substance that looks like the drug)

some show the placebo effect where they believe a treatment is working because they know they are given medicine

double blind study

phase 2 and 3 are double blind where neither the doctor or the patient know if they have been given a placebo/old drug or the new drug

reduces bias

attitudes cannot affect the results