Drug Testing

William Withering & Digitalis

  • William Withering was a scientist in the 1700s
  • He discovered that an extract of foxgloves could be used to treat dropsy (swelling caused by heart failure) the extract contained the drug digitalis
  • Withering made a chance observation - a patient suffering from dropsy made a good recovery after being treated with the traditional remedy containing foxgloves. Withering kew foxgloves were poisonous, so he started testing different versions of the remedy with different concentrations of digitalis (his digitalis soup)
  • to much digitalis poisoned his patients, and too little had no effect
  • it was thought this method of trial and error allowed him to discover the correct amount to give to a patient
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Modern Drug Testing

Drug testing is highly controlled - before a drug is tried on live subjects, computers are used to model the potential effects. Tests are carried out on human tissue in a lab, then on live animals, before clinical trials are carried out on humans. There are three test phases:

  • phase 1 involves testing a new drug on a small group of healthy individuals to find out things like safe dosage, side effects, and how the body reacts to the drug
  • phase 2 is  drug passes phase 1, it is then tested on a large group  of patients to see how well the drug actually works
  • phase 3 the drugis compared to existing treatments - it involves testing the drug on 100s of patients, they're randomly split into 2 groups (one receives the new treatment and the other has an existing treatment to see if the new drug is better than current treatments)
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Improving Reliability of Trials


One of the two groups in phase 2 is given the new drug, and the other is given a placebo. Patients often show a placebo effect - showing an improvement because they believe they are receiving treatment. Giving half the patients a placebo allows researchers to see if the drug actually works (if it improves pateints more than the placebo does).

Double Blind Study Design

Phase 2 and 3 clinical trials are usually double blind,This reduces bias in the results because the attitudes of the patients and doctors can't affect the results.

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Core Practical: Antimicrobial Properties of Plants

  • take extracts from the plants you are testing (garlic + mint) then dry and grind each plant, before soaking them in ethanol (which acts as a solvent) the plants should all be the same size so the amount of extract is the same
  • filter off the liquid (the ethanol containing dissolved plant extract)
  • evenly spread a sample of bacteria onto an agar plate
  • dip discs f filter paper in the extracts - they should be the same size so they will absorb the same volume of liquid
  • make a control disc (only soak in ethanol) to see if it's the ethanol or the paper that's inhibiting growth)
  • incubate the plate to allow the bacteria to grow
  • where the bacteia can't grow, there will be a clear patch in the lawn of bacteria (the inhibition zone - the larger the zone, the more effective the plant extarct is at killing bacteria)
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