STIP 3.1 Flashcards
define pharmacodynamics
the mechanics of interactions between drugs (and receptors, etc…)
define pharmacokinetics
what happens to drugs in the bdoy - how they are distributed, etc….
What does ADME stand for?
Absorption
distribution
metabolism
excretion
Rather than the EC50, what is used in pharmacokinetics?
ED50
ADME depends on drug structure - three factors of this?
ability to cross membranes
binding to proteins, enzymes, and carriers
solubility in water and fat
absorption define
getting the drug into the systemic circulation
Traits of oral absorption
- drug needs to dissolve
- must survive conditions in GI tract
- must be able to cross epithelial membranes
- needs to get into body before elimination in faeces
in what ways can drugs cross the epithelial membrane?
- passive diffusion (uncharged drugs)
- facilitated diffusion
- active transport
Bioavailability
fraction of a drug that is administered, reaching the systemic circulation
Distribution
the process of a drug moving between body compartments/tissues
- brain
- muscle
- fat
How to find out volume of distribution?
- give person known amount of drug (i.e. 100mg)
- take sample of plasma
- work out conc. of drug in plasma
- plasma volume = 4 L so
- [drug] = 25mg/L
Factors affecting distribution
- may be fat soluble - will accumulate in fatty tissues and very little will stay in blood
- may be bound to proteins in the blood - this will prevent distribution to the tissues
what are the problems with fat soluble drugs?
- accumulate slowly in fat (fat is poorly perfused)
- can be difficult to acheive a steady plasma level
- when drug is discontinued, slowly leaks out of fat over an extended period
what are some examples of fat soluble drugs?
- amiodarone
- thiopentone
