Chapter Answers

1. Outline the different classes of drugs and the two groups of prescribers.

Answer: 

  • General Sales List (GSL) drugs can be sold without supervision, e.g. in a supermarket or shop.

  • Pharmacy (P) medicines are those which are not included in the GSL or the POM (below) groups and can only be sold in registered premises under the supervision of a pharmacist. They do not need a prescription.

  • Prescription Only Medicines (POM) can only be provided by a pharmacist in registered premises in response to a prescription written by an authorised prescriber.

2. Identify and briefly describe the main terms used to describe types of drugs.

Answer: 

  • Agonists: (activators) which interact with a receptor and alter the cell machinery e.g. by enhancing the activity of an enzyme which alters a specific mechanism
  • Antagonists: (inhibitors) interact with a receptor and thus prevent other molecules binding with that receptor, preventing activation of the particular mechanism

They can also be described in the following terms:

  • Chemicals normally synthesised within the body, e.g. hormones
  • Substances not created within the body, called xenobiotics
  • Poisons: substances that are almost always harmful. However, almost any substance can be harmful in large enough dosages
  • Toxins: poisons created by biological organisms

3. Outline how drugs act on the body.

Answer: Drugs interact with receptors in the cell membrane which usually interact with molecules formed within the body to regulate cell function. The degree of drug action is dependent on the drug level in the blood stream and thus available to interact with the appropriate The level at which the drug is effective is the level at which the drug is effective is The drug molecule has to be the specific size and shape to interact (like a lock and key) with the precise receptor it is to effect, and can vary considerably in size, complexity and duration of action. Each drug works by modifying a particular aspect of cell function.

4. Identify and briefly describe the four stages of pharmacokinetics.

Answer: The concentration of the drug in the tissue fluids and level of activity is determined by the balance between the four pharmacokinetic processes of

  • Absorption: drug moves from site of administration into bloodstream
  • Distribution: drug distributed in bloodstream first to parts of body with biggest blood supply and then to almost all parts of body
  • Metabolism: largely in the liver, drug molecule is altered into different form, may be inactive, more of less active, or more soluble for excretion
  • Excretion: some from liver into bile and small intestine, other drugs excreted through kidneys in the urine

5. Specify the main routes for administration of drugs.

Answer: 

  • Enteral route: oral administration absorption through stomach or intestine
  • Rectal administration
  • Parenteral routes: outside GIT, mainly intramuscular and subcutaneous injection
  • Topical routes: apply to body surface, e.g. skin, vagina, eyes/ears/nose, lungs

6. What do you understand by first-pass metabolism? How can it be avoided?

Answer: Following absorption into portal circulation, drug carried to liver and some is converted into inactive molecules and excreted. It can be avoided by administering drug through route which will not lead to absorption into the portal circulation, e.g. topical routes, injections, rectally.

7. Outline the essentials of drug administration.

Answer: 

  • Correct patient: patient details must correspond with name on ID band.

  • Appropriate prescription: drug details on prescription must be correct, i.e. dose appropriate for patient (in relation to normal dose, strengths, patient’s condition, dose, route, time all specified. Date of expiry must be checked.

  • Administration: must be correct, i.e. prescription checked carefully against drug container. Drug administered to the patient in person.

    • Check for any side-effects before administration.

    • The dosage must match the prescription.

    • The route of administration must be as specified.

    • Correct time of administration for each drug must be adhered to.

  • Recording: Accurate records completed and signed by responsible person.

  • Adverse reactions reported.

8. Briefly discuss the potential difficulties in drug administration with older people.

Answer: Pharmacokinetics is different in older adults so dosages need to be different. Polypharmacy must be considered with numerous disorders needing treatment.

  • Absorption: reduced absorption – emptying slowed, blood flow reduced, villi flattened
  • Distribution: body water reduced, plasma proteins less, decreased body mass, increased fat
  • Metabolism: reduced liver metabolism as lower liver enzymes and blood flow
  • Excretion: slowed due to reduced nephrons and lower glomerular filtration

9. Outline the types of adverse drug effects (ADRs) that can occur and consider how these can be limited.

Answer: 

  • Known effect of drug: stronger than normal related to dose and individual’s susceptibility to the drug. Accurate administration and careful observation are essential. Many such adverse effects are reversible if dosage is reduced.
  • Unrelated to known action of drug: may be unrelated to the therapeutic can range from mild to very severe. Some ADRs are predictable if drug is taken in excess, e.g. excessive paracetamol results in liver damage.

Some groups of ADRs unrelated to therapeutic actions may occur with a normal dose:

  • Idiosyncratic reactions: tend to be serious, unpredictable and uncommon, may cause damage to organs, e.g. liver, kidneys
  • Immunological reactions: allergic reactions occur in some individuals, individuals need to know how to deal with them. Can be minor to life-threatening
  • Anaphylactic shock: release of histamine etc. à rash, tissue swelling, bronchospasm, and hypotension, and may be lethal
  • Haematological reactions
  • Allergic liver damage
  • Skin eruptions from mild rashes to life-threatening skin loss
  • Carcinogenesis and fetal abnormalities: some drugs can cause mutations in DNA resulting in cancers, or can cause a range of fetal abnormalities

ADRs can be reduced by:

  • Care in administration
  • New drugs developed through a number of stages (see Table 4.5) to reduce the risk of ADRs.