Preventing and treating disease

• Antibiotics


  Medicines that can kill bacteria in the body
• Antibiotics


  • Specific bacteria need to be treated by specific antibiotics
  • Antibiotics have greatly reduced deaths from infectious bacterial diseases, but antibiotic-resistant strains of bacteria are emerging
• Treating viral diseases


  • Antibiotics do not affect viruses
  • Drugs that kill viruses often damage the body's tissues
  • Painkillers treat the symptoms of viral diseases but do not kill the virus
• Discovering and developing new drugs

  1. Drugs were traditionally extracted from plants and microorganisms

  2. Most modern drugs are now synthesised by chemists in laboratories

  3. New drugs are extensively tested and trialled for toxicity, efficacy, and dose
• Examples of drugs from natural sources

  • The heart drug digitalis comes from foxglove plants
  • The painkiller aspirin originates from willow trees
  • Penicillin was discovered by Alexander Fleming from Penicillium mould
• Stages of clinical trials

  1. Pre-clinical trials: Drug is tested in cells, tissues, and live animals

  2. Clinical trials: 1. Healthy volunteers receive very low doses to test whether the drug is safe, 2. If safe, larger numbers of patients receive the drug to check it is effective and find the optimum dose
• Peer review


  Before being published, the results of clinical trials will be tested and checked by independent researchers
• Double-blind trials


  Some clinical trials give some of their patients a placebo drug, and neither the patients nor the doctors know who has been given the real drug and who has been given the placebo
• Non-specific defences of the human body against all pathogens

  • Skin: physical barrier, antimicrobial secretions, microorganisms that prevent pathogens growing
  • Nose: Cilia and mucus trap particles in the air, preventing them from entering the lungs
  • Stomach: Produces strong acid (pH 2) that destroys pathogens in food and drinks
• White blood cells


  • Lymphocytes: Produce antitoxins that bind to toxins produced by pathogens, and antibodies that target and help destroy specific pathogens
  • Phagocytes: Attracted to areas of infection, surround and engulf pathogens, enzymes digest and destroy the pathogen
• It is a common misconception that antibiotic resistance arises when people become resistant to a drug. In reality, it is the bacteria that evolve resistance.