Biopharmaceutics Flashcards
what is the definition of biopharmaceutics?
the study of how the physiochemical properties of the drug, the dosage form and the route of administration effect the rate and extent of drug absorption
what is the definition of pharmacokinetics?
the study and characterisation of the time course of drug absorption, distribution, metabolism and excretion
what is the definition of pharmacodynamics?
the study of the biochemical and physiological effects of the drug on the body
distribution is governed by affinity for various tissues, it depends on: (3)
- aqueous or lipid solubility
- binding to extracellular substances e.g proteins
- intracellular uptake
what is passive diffusion and does to involve carriers?
- movement via concentration gradient across a membrane separating two body compartments
- does not require a carrier
- it is not saturable
- this is how the majority of drugs gain access to the body
what is the lipid-aqueous drug partition coefficent?
describes the ease with which a drug moves between aqueous and lipid environments
what is endocytosis and exocytosis? give an example
they are processes that mediate entry into cells by very large substances (for example: movement across intestinal wall into blood of vitamin b12 complexed with its binding protein)
what does the therapeutic response depend on?
adequate concentration at the site of action
what happens when you adjust plasma concentration?
it adjusts the response
what is bioavailability?
a measure of the amount of drug from a formulation that appears in the plasma i.e measure of the rate and extent of absorption
how can bioavailability be calculated?
by determining the AUC (area under curve) from a blood plasma drug concentration versus time plot
what is the definition off bioequivalence?
comparing if two dosage forms containing same drug are equivalent in terms rate and extent of absorption
what is absolute bioavailability?
Fraction of administered dose absorbed into the systemic circulation (accounting for different oral/iv doses)
where can drugs distribute? (3)
- plasma (3L)
- interstitial fluid (10L)
- intracellular fluid (28L)
what factors affect drug distribution and how? (2)
- aqueous or lipid solubility: only the un-ionised form will diffuse across membrane
- blood flow: parts of the body which receive the most blood flow gets the most drug
what is the equation to work out the dose?
dose= vol x cons
metabolism= ?
biotransformation
what is biotransformation?
any process which results in a chemical change in a drug in the body
where are metabolic processes most likely to occur? (4)
liver, kidneys, lungs and GI tract
what is the process of cleavage?
the splitting of the molecule into 2 or more simpler molecules
what is oxidation?
combining the molecule with oxygen, or increasing the electropositive charge by the loss of hydrogen or of one or more electrons
what is conjugation?
the combining of the molecule with glucuronic or sulphuric acid
what is reduction?
the molecule gains 1 or more electrons and become more negatively charged
how does elimination occur in the kidneys?
glomerular filtration: drug crosses the glomerular filter to be excreted
how does elimination occur in the liver?
changes a lipid soluble molecule to a more water soluble molecule to be excreted in the kidneys
what is half-life?
the time taken for concentration to decrease to half its value
