Option B : Medicines and Drugs

The aim of this option is to give students an understanding of how drugs and medicines can influence the functioning of the body. Students should be able to recognize the fundamental structures and relevant functional groups of several classes of drugs and medicines (as listed below or in 11.3.1), and should be able to distinguish between them. Memorizing of complex formulas is not required. Throughout the option, stress the contribution that science has made (and continues to make) toward maintaining and improving the health and well-being of the world's population.

B.1         Pharmaceutical Products (2h)

B.1.1      List the effects of drugs and medicines.
                    Generally a drug or medicine is any chemical which does one or more of the following :

  •                  alters incoming sensory sensations
  •                  alters mood or emotions
  •                  alters physiological state, including consciousness, activity level or coordination.


                  Stress the importance of the body's natural healing processess and the placebo effect.

    B.1.2     Outline the stages involved in research, development and testing of new pharmaceutical products.
                  Refer to the Thalidomide case as an example of what can go wrong. The use of combinatorial chemistry is not
                  required here, but is covered in B.8.4.

    B.1.3     Describe the different methods of administering drugs.
                        The four main methods are oral, rectal, inhalation and parenteral (by injection). Injections may be intravenous,
                        intramuscular or subcutaneous.

    B.1.4     Discuss the terms lethal dosage(LD50),tolerance and side effects.
                        LD50 is the lethal dose required for 50% of the population.

                        A person who develops tolerance requires a large dose of a drug in order to achieve the effect originally obtained
                        by a smaller dose. Stress that the difference between the main effect and side effects is relative. For example,
                        morphine is often used as a pain killer with intestinal constipation being a side effect. For a person with diarrhoea
                        the constipation induced becomes the main effect, with the pain relief a side effect. The risk : benefit ratio should
                        be considered.

    B.2         Antacids (1h)

    B.2.1     State and explain how excess acidity in the stomach can be reduced by the use of different bases.
                        Examples should include aluminium and magnesium compounds and sodium hydrogencarbonate. Students should
                        be able to write balanced equations for neutralization reactions and know that antacids are often combined with
                        alginates (which produce a neutralizing layer preventing acid in the stomach from rising into the esophagus and
                        causing heartburn), and with anti-foaming agents (such as dimethicone).

    B.3         Analgesics (3h)

    B.3.1      Describe and explain the different ways that analgesics prevent pain.
                        Mild analgesics function by intercepting the pain stimulus at the source, often by interfering with the production of
                        substances (eg. prostaglandins) that cause pain, swelling or fever. Strong analgesics work by temporarily bonding
                        to receptor sites in the brain, preventing the transmission of pain impulses without depressing the central nervous
                        system.

    B.3.2     Describe the use of derivatives of salicyclic acid as mild analgesics and compare the advantages and disadvantages of
                  using aspirin and paracetamol (acetaminophen).
                        Aspirin has been found to be useful in preventing the recurrence of heart attacks. The disadvantages of aspirin
                        include ulceration and stomach bleeding, allergic reactions and Reye's syndrome in children (a potentially fatal
                        liver and brain disorder). Paracetamol is very safe in the correct dose but can, rarely, cause blood disorders and
                        kidney damage. Overdosage can lead to serious liver damage, brain damage and even death.

    B.3.3     Compare the structures of morphine, codeine and the semi-synthetic opiate, heroin.
                        Stress the simple modification to the structures of morphine which results in the semi-synthetic drug, heroin.

    B.3.4     Discuss the advantages and disadvantages of using morphine and its derivatives as strong analgesics.
                        Include the social as well as physiological effects of both short- and long- term use.

    B.4         Depressants (3h)

    B.4.1      Describe the effects of depressants.

                        At low doses a depressant may exert little or no effect. At moderate doses the compound may induce
                        sedation(soothing, reduction of anxiety). At higher doses it may induce sleep and at extremely high doses it may
                        cause death. Depressants are often described as anti-depressants because they relieve depression.

    B.4.2     Discuss the social and physiological effects of the use and abuse of ethanol.
                        Include effects on the family, cost to society and the short- and long-tem health effects.

    B.4.3     Describe and explain the techniques used for the detection of ethanol in the breath and in the blood or urine.
                        Include potassium dichromate (VI) in the breathalyser, analysis of blood or urine by chromatography and
                        absorption of infra-red radiation in the intoximeter.

    B.4.4     Describe the synergistic effects of ethanol with other drugs.
                        Examples include increased risk of stomach bleeding with aspirin, and increased risk of heavy sedation with any
                        drug that has a sedative effect on the central nervous system.

    B.4.5     List other commonly used depressants and describe their structures.
                        Limit this to a brief mention of the use of diazepam (Valium ), nitrazepan (Mogadon ) and fluoxetine
                        hydrochloride (Prozac ).

    B.5        Stimulants (2.5h)

    B.5.1     List the physiological effects of stimulants.

    B.5.2     Compare amphetamines and adrenaline.
                        Amphetamines and adrenaline are chemically similar in that both derive from the pheylethylamine structure.
                        Amphetamines mimic the effects of adrenaline and are known as sympathomimetic drugs.

    B.5.3     Discuss the short - and long-term effects of nicotime consumption.
     

  •                 Short-term effects : increased heart rate and blood pressure and reduction in urine output, as well as stimulating
  •                 effects.
  •                 Long-term effects : increased risk of heart disease, coronary thrombosis and peptic ulcers. Discuss also the
  •                 addictive properties of nicotine and the further risks associated with smoking tobacco.


    B.5.4     Describe the effects of caffeine and compare its structure with that of nicotine.
                        Caffeine is a respiratory stimulant. When consumed in large amounts it can cause anxiety, irritability and
                        sleeplessness. It is a weak diuretic. Both caffeine and nicotine contain a tertiary amine group.

    B.6         Antibacterials (2h)

    B.6.1     Outline the historical development of penicillins.
                        Include the discovery by Fleming and the development by Florey and Chain.

    B.6.2     Compare broad-spectrum and narrow spectrum antibiotics.

    B.6.3     Explain how penicillins work and discuss the effects of modifying the side chain.
                        Penicillins work by interfering with the chemicals that bacterial need to form normal cell walls. Modifying the side
                        chain results in penicillins which are more resistant to the penicillinase enzyme.

    B.6.4     Discuss and explain the effect overprescription of penicillins has, and the use of penicillins in animal feedstock.

    B.7         Antivirals (1.5 h)

    B.7.1     State how viruses differ from bacteria.

    B.7.2     Describe the different ways in which antiviral drugs works.
                        Antiviral drugs may work by altering the cell's genetic material so that the virus cannot use it to multiply.
                        Alternatively they may prevent the viruses from multiplying by blocking enzyme activity within the host cell.

    B.7.3     Discuss the difficulties associated with solving the AIDS problem.
                        Specific proteins on the HIV virus bind to a receptor protein on certain white blood cells (T cells). Because of the
                        ability of the HIV viruses to mutate and because their metabolism is linked closely with that of the cell, effective
                        treatment with antiviral drugs is very difficult, as is vaccine development.

    B.8         Stereochemistry in Drug Action and Design (3h)

    B.8.1     Describe the importance of geometrical isomerism in drug action.
                        Students should be aware that cis- and trans-isomerism can occur in inorganic complexes and that the two
                        different isomers can have different pharmacological effects. The anti-cancer drug cisplatin is a good example.

    B.8.2     Discuss the importance of chirality in drug action.
                        The two enantiomers in a racemic mixture of a drug may have very different effects, eg Thalidomide. One
                        enantiomer of Thalidomide alleviates morning sickness in pregnant women, whilst the other enantiomer causes
                        deformities in the limbs of the fetus.

    B.8.3     Describe the use of chiral auxiliaries to form the desired enantiomer.
                        A chiral auxillary is used to convert a non-chiral molecule into just the desired enantiomer, thus avoiding the need
                        to separate enantiomers from a racemic mixture. It works by attaching itself to the non-chiral molecule to create
                        the stereochemical conditions necessary to force the reaction to follow a certain path. Once the new molecule has
                        been formed the auxiliary can be taken off (recycled) to leave the desired enantiomer. An example is the synthesis
                        of Taxol, an anti-cancer drug.

    B.8.4     Explain the use of combinatorial chemistry to synthesize new drugs.
                        Combinatorial chemistry is used to synthesize a large number of different compounds and screen them for
                        biological activity, resulting in a 'combinatorial library' (for example the 'mix and split' process whereby
                        polypeptides can be made by every combination of amino acids, using polystyrene resin beads). Stress the
                        importance of solid phase chemistry.

    B.9         Anesthetics (2h)

    B.9.1     Compare local and general anesthetics in terms of their mode of action.

    B.9.2     Compare the structures and effects of cocaine, procaine, and lidocaine.

    B.9.3     Discuss the advantages and disadvantages of nitrous oxide, ethoxyethane and trichlorometane, cyclopropane and
                  halothane
                    Nitrous oxide is not very potent, trichloromethane leads to liver damage, ethoxyethane and cyclopropane are highly
                    flammable. Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is widely used but is potentially harmful to the
                    ozone layer.

    B.9.4     Calculate the partial pressures of component gases in an anesthetic mixture.
                    Knowledge of how to use Dalton's law of partial pressures is required. Students are not expected to state the law.

    B.10         Mind-altering drugs (2h)

    B.10.1     Describe the effects of lysergic acid diethylamide (LSD), mescaline, psilocybin and tetrahydrocannabinol (THC).

    B.10.2     Discuss the structural similarities and differences between LSD, mescaline and psilocybin.
                        Stress the similarity of all three drugs and compre them to the indole ring.

    B.10.3     Discuss the arguments for and against the legalization of cannabis.
                        Arguments for legalisation include the ability of cannabis to offer relief for certain disease. Arguments against
                        legalization include the possible harmful effects and the possibility of cannabis users moving on to harder drugs.


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