Principles of Pharmacology Flashcards
Define the term drug
Drug is an active ingredient of a medicine. It is any substance which interacts with a biological system and changes it.
What are the effects of these drugs? Antacids Bulk laxatives Osmotic laxatives Osmotic diuretics General anaesthetics Alcohol
Antacids = Neutralise acid
Bulk laxatives = Speed up digestive transit
Osmotic laxatives = retaining water and speeds up digestive transit
Osmotic diuretics = Puts more water into the urine
General anaesthetics = Controlled unconsciousness
Alcohol = ethanol prevents the toxicity of methanol
What is potency?
How well a drug works. It is the lowest concentration to show an effect.
What does biological specificity mean?
Characteristic such as behaviour or a biochemical variation
What does chemical specificity mean?
Stereoisomers (mirror images) can have major differences
How does the isolated ileum experiment help us understand what affects the ANS
When the ileum muscle contracts it pull down the transducer and makes a recording on the pen reader. This allows for evaluating agents that affect the autonomic nervous system. When different drugs eg Ach is added we can monitor the effects of contraction when histamine is added then atropine and see the effects of contraction. In this cause contraction was not allowed after atropine was added.
How do drugs produce there effect when binding to receptors?
Drug produce their effect by binding to specific receptor sites in the cell. The response is a function of the number of occupied receptors.
The lock and key hypothesis:
The shape of the drug complements the shape of the receptor = chemical specificity.
Affinity = The strength of the drug receptor interaction
What is an agonist?
Agonist binds to a receptor and produces a response.
Possess affinity and efficacy
Eg. Acetylcholine and histamine
What is an antagonist?
Binds to a receptor but does not produce a response.
Competitive antagonists prevent agonist binding and so prevents the response to an agonist.
Possess affinity but not efficacy
Eg. Atropine and mepyramine
What does affinity mean?
The affinity of a drug for its receptors is a measure of how well it binds to the receptor.
The affinity can be measured using a drugs dissociation constant from its receptor, the Kd. This is equal to the concentration at which, half the receptors will be bound with a drug.
What does efficacy mean?
Efficacy is the measure of the degree to which an agonist produces a response when binding to a given proportion of receptors.
For a full agonist, efficacy = 1
For a partial agonist, efficacy = <1 but >0
In some cases it is possible to have a negative efficacy, in which the drug is an inverse agonist.
What are the two ways of displaying the relationship between drug concentration and response?
- Linear-linear (Hyperbola). This can be displayed at a %, however is it more difficult to quantify values on a linear-linear graph.
- Log-linear Semi log graph (Sigmoid). It is easier to quantify values on a log-linear graph than a linear-linear graph.
The relationship is graded, saturating and exhibits a threshold.
