PHARMACOLOGY Flashcards
What does ADME stand for?
Absorption
Distribution
Metabolism
Excretion
What is volume of distribution?
The fluid in which a drug seems to be dissolved
What is the calculation used to calculate the volume of distribution?
Vd = Total mass of drug in the body / Concentration of the drug in the plasma
What is indicated if a drug has a Vd value greater than 1 litre/kg?
Indicates the drug is accumulating in other body compartments (e.g. fat)
Which Vd value indicates a drug has distributed within the plasma?
0.05 litres/kg
Which Vd value indicates a drug has distributed into the extracellular fluid?
0.2 litres/kg
Which Vd value indicates a drug has distributed into the total body water (tissues etc.)?
0.55 litres/kg
When would a loading dose of a drug be required?
A loading dose is used for drugs which have a high Vd value
What is the calculation used to calculate the loading dose of a drug?
Loading dose = Vd x Ceff
Ceff = effective plasma concentration
List three factors that can affect the volume of distribution of a drug
Species
Age
Disease
What is the purpose of drug metabolism?
To increase the water solubility of the drug
What are the two phases of drug metabolism?
Phase 1 (functionalisation)
Phase 2 (conjugation)
Describe what happens when a drug undergoes phase 1 (functionalisation) metabolism
The drug is functionalised into a derivative via the exposure of a functional group
Describe what happens when a drug undergoes phase 2 (conjugation) metabolism
The drug is conjugated into an inactive conjugate via the addition of a large polar side chain to the exposed functional group
List the four possible reactions that a drug can undergo during phase 1 (functionalisation) metabolism
Oxidation
Reduction
Hydrolysis
Hydration
Which group of enzymes are responsible for drug metabolism?
Microsomal enzymes
Which specific group of enzymes are involved in phase 1 (functionalisation) metabolism?
Cytochrome P450 enzymes
What is presystemic metabolism?
When the liver or gut wall metabolises the drug before it reaches the systemic circulation
What are some of the consequences of presystemic metabolism?
Poor bioavailability
Larger drug dose needed
What are the possible consequences of drug induced synthesis of microsomal enzymes?
Increased metabolism which can cause either an increase or decrease in toxicity depending on the nature of the produced derivative
List three examples of drugs which induce the synthesis of microsomal enzymes
Phenobarbitone
Rifampicin
Ethanol
Can drug induced synthesis of microsomal enzymes affect the metabolism of other drugs as well?
YES
List five factors that can affect drug metabolism
Previous drug therapy
Age
Disease
Species
Inter-individual variation
What is clearance?
The efficiency of the irreversible elimination of a drug from the systemic circulation
What is enterohepatic circulation?
The circulation between the small intestine and the liver used to recycle compounds
Which type of kinetics do most drugs exhibit in practice?
First order kinetics
- Drug concentration declines exponentially with time
K(abs)
Rate constant for absorption
K(exc)
Rate constant fot excretion
K(met)
Rate constant for metabolism
C(t)
Concentration at time ‘t’
Cl(s)
Total clearance of the drug
Which pharmacological concept is presented in a concentration response curve?
The response to a drug is ‘dose dependent’ i.e. the more drug given, the bigger the cellular response
What is the EC50 of a drug and what can this value be used for?
The EC50 value of a drug is the concentration of the drug which generates half of the maximum response. This can be useful in drug comparison
(T/F) There can be alterations in drug receptor activity causing alterations to the concentration response curve
TRUE
What are the terms used to describe a rapid decrease in drug receptor activity?
Desensitisation/tachyphylaxis
What are the terms used to describe a more gradual decrease in drug receptor activity?
Tolerance/refractoriness
What is the term used to describe no drug receptor activity/resistance to drug activity?
Resistance
Briefly describe how an agonist (drug) elicits a cellular response
- OCCUPATION: Drug (agonist) binds to its specific receptor via affinity forming an inactive reversible drug receptor complex
- ACTIVATION: Reversible drug receptor complex is activated by efficacy leading to a cellular response
What is affinity?
The measure of the attraction between a drug and its receptor
What is efficacy?
The ability of a ligand/drug to elicit a cellular response when bound to its receptor
How does antagonism prevent or reduce a cellular response?
Antagonists have no efficacy
Describe how competitive antagonism decreases cellular effects
The antagonist competes with the agonist for the receptor binding site, inhibiting the agonist from binding and thereby reducing the cellular effect. This can be reversible or irreversible
Briefly describe how reversible competitive antagonists interact with receptors
Reversible competitive antagonists can bind and dissociate from the receptor and the addition of more agonists can reverse the affects of reversible competitive antagonists
Describe the appearance or graphs displaying the relationships between reversible competitive antagonists interact and receptors
Parallel shift
- the addition of more agonists can reverse the effects of reversible competitive antagonists allowing maximum response to be reached
Briefly describe how irreversible competitive inhibitors interact with receptors
Irreversible competitive antagonists bind and dissociate very slowly or not at all
Describe the appearance or graphs displaying the relationships between irreversible competitive antagonists interact and receptors
Reduction in maximum response
- agonists are unable to bind to their receptors due to the actions of the antagonist, preventing reaching the maximum response
How does physiological antagonism work?
Apposing physiological actions cancel each other out
How does chemical antagonism work?
Two substances combine in solution and cancel each other out i.e. chelating agents
