Ch. 5 Pharmacodynamics

Question 1

what is pharmacodynamics

Answer 1

study of biochemical and physiologic effects of drugs and molecular mechanisms by which those effects are produced

*how drugs work once they’re in the body

Question 2

Dose-Response Relationship

Answer 2

• dose matters: takes a certain dose to have an effect
• maximal efficacy: even if you increase dose, no additional effect will be achieved
• potency: amount of drug that must be given to elicit an effect
  - potent elicits effects at
  low doses
  - doesn’t mean one
  superior- only is the dose is so high that it becomes inconvenient

Question 3

Drug-Receptor interactions

Answer 3

• drugs are chemicals
• receptors are chemicals in the body that the drug must find to have its effect

Question 4

Drug receptor equation

Answer 4

drug+receptor <-> drug receptor complex forms-> response

Question 5

drug receptor interactions

Answer 5

• drug receptor complexes act on already-existing physiologic processes
• receptors cannot give cells new function, but can only change pre-existing body processes
• receptors can mimic or block the action of the body’s own chemicals
• drugs help the body use its pre-existing chemicals

Question 6

Drug-receptor interactions

Answer 6

receptors and selectivity

• more selective=fewer side effects
• body has many receptors for chemicals/drugs
• if drug interacts with only a FEW receptors-> then limited drug response
• if drug interacts with MANY receptors-> then wide variety of responses may occur
• just because a drug is highly selective, does NOT mean its more safe
  - EX. morphine acts on pain receptors to reduce pain BUT also acts on other receptors causing respiratory depression, etc

Question 7

drug receptors interactions

Answer 7

• the more receptors that are occupied by drug will create a more intense effect of that drug
• maximal response will occur when all receptors are occupied
• Affinity: attraction of the drug to the receptor site
  • high affinity= bind at low doses, making them very potent
  • low affinity= bind at higher doses=weak or not very potent drug

Question 8

Drug receptor interactions: Agonists

Answer 8

• mimic the body’s actions and activates the body’s receptors
• agonists can have many effects, and not necessarily making body processes faster

Question 9

Drug receptor: antagonists

Answer 9

• prevent receptor activation in the body
• can block the body’s own chemicals, can block drugs in the body, can block agonist
• if no agonist is present, then antagonist will not have anything to do and will not have measurable effect

Partial agonist: not as strong as a full agonist and/or antagonist

ex. acetylcholine acts on cholinergic receptors in heart to decrease function

Question 10

Drug responses that do not involve receptors

Answer 10

• some drugs do not use receptors to provide their effects (react with other molecules without a receptor)
• Receptor-less drugs
  • antacids act directly with molecules in
    stomach acid
  • antiseptic alcohol causes breakdown n of
    bacterial proteins
  • magnesium enemas can cause osmotic
    reaction to hold fluid in the bowel
  • chelating agents form complexes with
    heavy metals

Question 11

Interpatient variability in drug responses

Answer 11

• initial doses are approximate and later doses are adjusted as needed to treat the patient
• doses are adjusted based on how the patient responds to the drug

Question 12

Therapeutic index

Answer 12

1. measure of a drug’s safety
2. the higher the therapeutic index, the safer the drug
3. drugs with a low therapeutic index are as equally effective as they are harmful