Pharmacology Flashcards
What is pharmacodynamics?
What a drug does to the body (biological effects and mechanism of action)
What is pharmacokinetics?
What the body does to a drug (absorption, distribution, metabolism and excretion of drugs and their metabolites)
What kinds of regulatory proteins do drugs bind to?
Enzymes Carrier molecules (transporters and pumps) Ion channels Receptors RNA & DNA
What is an agonist?
A drug that binds to a receptor to produce or enhance a cellular response
What is an antagonist?
A drug that blocks the actions of an agonist
What is affinity?
The strength of association between ligand and receptor
What is efficacy?
The ability of an agonist to evoke a cellular resonse
What is the relationship/shape of the graph between concentration of agonist and % response? (On a linear plot)
Hyperbolic
What is EC50 or ED50?
The concentration of agonist that elicits a half maximal response
What is the relationship/shape of the graph between concentration of agonist and % response? (On a semi-logarithmic plot)
Sigmoidal
Why is it useful to plot concentration against response graphs on a semi-logarithmic plot?
To get a more accurate determination of ED50
What are the four factors which control drug absorption?
Solubility
Chemical stability
Lipid to water partition coefficient (rate of diffusion increases with the lipid solubility of the drug)
Degree of ionisation
Many drugs exist as weak acids or weak bases existing in both ionised (A-, BH+) and unionised (AH, B) forms. Which forms diffuse readily across the lipid bilayer?
Only unionised forms
What is the pKa of a drug?
The pH at which 50% of the drug is ionised
How can the proportion of unionised drugs be determined?
Henderson-Hasselbalch equation
Where could weak acids be absorbed?
Stomach - pH of stomach lumen facilitates absorption
Where are bases absorbed?
Small intestine
Are weak or strong acids and bases absorbed better?
Weak acids and bases are absorbed better
Where does the majority of absorption occur?
Small intestine (Even weak acids despite pH of stomach lumen being ideal for absorption)
What is the definition of systemic availability?
Amount of drug in systemic circulation/amount absorbed
What is the systemic availability of IV drugs?
100%
What are the enteral routes of drug administration?
Oral
Sublingual
Rectal
What are the parenteral routes of drug administration?
Intravenous
Intramuscular/subcutaneous
Inhalational
Topical
Drugs administered by which routes pass through the liver?
Oral
Some of the drug administered in rectal route will pass through liver
Drugs administered by which routes enter the systemic circulation?
Buccal/sublingual Transdermal/subcutaneous Intravenous Rectal Intramuscular
Which kind of drugs move between fluid compartments/across membranes readily?
Unionised
Are drugs able to move freely by diffusion bound to protein?
No
What is the volume of distribution (Vd)?
The apparent volume in which a drug is dissolved
Dose/plasma concentration
What does a Vd of <5L imply?
The drug is retained in the vascular compartment
What does a Vd of <15L imply?
The drug is restricted to extracellular water?
What does a Vd of >15L imply?
The drug has been distributed throughout total body water e.g. highly lipid soluble drugs like ethanol
What kind of drugs will not cross the phospholipid bilayer?
Polar
What is the equation for initial concentration (Co)?
D/Vd
(Dose, D
Volume of distribution, Vd)
What is first order kinetics?
Where the rate of elimination is directly proportional to drug concentration
What is zero order kinetics?
The rate of elimination remains constant, independent of plasma concentration
How can the rate of elimination be calculated?
Cp x Cl
(Plasma concentration, Cp
Clearance, Cl)
How can the rate of elimination be calculated from a graph?
Given by the tangent to the curve
The higher the plasma concentration, the steeper the curve
What are the units for rate of elimination?
mg/min
What is CSS?
Plasma steady-state concentration
How many half lives (roughly) does it take for a drug to reach CSS?
5
Which surface of the cell membrane has a negative potential?
Inner surface
Which direction does sodium move across a membrane?
Into the cell
Which direction does potassium move across a membrane?
Out of the cell
What is the resting potential of the cell membrane?
-70mV
What causes the upstroke of the neuronal action potential?
Opening of Na+ channels causing influx of Na+ and rapid depolarisation
What causes the downstroke of the neuronal action potential?
K+ opening and Na+ closing
What is the absolute refractory period?
The period of the action potential in which no stimulus, however strong, can illicit a second action potential
What is the relative refractory period?
The period in which a stronger than normal stimulus may illicit a second action potential
How does the action potential move along an unmyelinated nerve fibre?
Smoothly & continuously
How does the action potential move along a myelinated nerve fibre?
Jumps from one node of Ranvier to the next along the myelinated sheath
