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• Medicines and drugs


  Chemical substances that alter incoming sensory sensations, alter a person's mood or emotions, or alter the physiological state of the body including consciousness and coordination
• Drug


  A substance that causes a physiological change in the body
• Pharmaceutical drugs


  Used for the treatment or prevention of diseases
• Recreational drugs


  Chemical substances taken for enjoyment, or leisure purposes, rather than for medical reasons
• Recreational drugs


  • Alcohol, nicotine, cannabis, ecstasy
• Medicines (pharmaceutical drugs)


  Substances used for the treatment or prevention of disease
• Therapeutic effect


  The beneficial effect of a medicine
• Medicines


  • Aspirin, penicillin, ibuprofen
• Methods of drug administration


  • Oral
  • Inhalation
  • Skin patches
  • Suppositories
  • Eye or ear drops
  • Injection (parenteral)
• Parenteral methods of drug administration


  • Intramuscular
  • Subcutaneous
  • Intravenous
• Bioavailability


  The fraction of the administered dosage of a drug that enters the bloodstream and accesses the site of action
• Factors affecting bioavailability


  • Method of drug administration
  • Polarity (solubility) of the drug
  • Type of functional groups present in the drug
• Drugs administered intravenously have a bioavailability of 100% as they are delivered directly into the bloodstream
• Drugs administered orally are often broken down during digestion before reaching the bloodstream
• An oral dose of a drug needs to be about four times higher than the dosage of the same drug administered intravenously
• Polarity of a drug


  Affects its solubility
• Polarity and solubility


  • Very hydrophilic (polar) drugs are soluble in aqueous body fluid but poorly absorbed
  • Very hydrophobic (non-polar) drugs are also poorly absorbed because they are insoluble in aqueous body fluids
  • For a drug to be readily absorbed, it must be largely hydrophobic, but also have some solubility in aqueous solution
• Functional groups that enhance lipid solubility


  Non-polar, lack the ability to ionize or form hydrogen bonds
• Aspirin is a largely non-polar molecule and therefore has low solubility in water
• The solubility of aspirin can be increased by reacting it with aqueous sodium hydroxide (NaOH) solution forming an ionic salt
• Drugs which contain an acidic or basic group can be chemically modified to form an ionic salt (increasing their bioavailability)
• Therapeutic window


  A measure of the safety of a drug
• Types of therapeutic window


  • Wide therapeutic window: wide margin between effective and toxic doses
  • Narrow therapeutic window: only a small increase in effective dose may produce toxic effects
• Therapeutic index


  The ratio between the dosage of a drug that causes a toxic (or lethal) effect and the dosage that causes a therapeutic effect
• ED50 (median effective dose)


  The dose that produces the therapeutic effect in 50% of the population
• TD50 / LD50 (median toxic / lethal dose)


  The dose that is toxic / lethal to 50% of the population
• Stages in drug development


  1. Drug is synthesized in the laboratory

  2. The drug is tested on animals to determine the LD50

  3. The drug is tested on humans - half the group are given the real drug, the other half are given a placebo

  4. Patient and administration do not know who has received the drug and who has received the placebo
• Placebo effect


  When the body is fooled into healing itself naturally
• Factors determined during clinical drug trials

  • Risk:benefit ratio
  • Unwanted side effects
  • Drug tolerance - person needs to take ever larger quantities of a drug to gain the original effect
• Synthesis of aspirin


  1. Salicylic acid is reacted with ethanoic anhydride, with concentrated H2SO4 or H3PO4 as the catalyst

  2. The product is cooled to form crystals which are then suction filtered and washed with cold water

  3. The aspirin is purified through recrystallization by dissolving the impure crystals in a small volume of hot ethanol, then adding water and cooling slowly
• Pure aspirin has a melting point of between 128°C - 140°C
• Impurities lower the melting point of aspirin and cause it to melt over a wider temperature range
• Soluble aspirin


  Aspirin reacted with aqueous NaOH to form an ionic salt, increasing its solubility in aqueous solutions
• Converting aspirin to an ionic salt increases its solubility but does not increase its bioavailability
• The acetylsalicylate ion is converted back to the unionized form in the acidic environment of the stomach
• The bioavailability of aspirin can be increased by administering it intravenously
• Mild analgesic


  Blocks the sensation of pain at the source
• Aspirin


  Works by blocking the action of the enzymes that produce prostaglandins, which are involved in the transmission of pain impulses to the brain, as well as causing fever and swelling
• Anticoagulant


  A class of drugs that work to prevent the blood from clotting
• Aspirin is effective in the prevention of the recurrence of heart attacks and strokes