Segars: Introduction to Pharmacokinetics Flashcards
What is pharmacodynamics?
-how the drugs affect the body
what is pharmacokinetics?
-how the body affects the drugs
What is ADME?
- Absorption
- Distribution
- Metabolism
- elimination
what is the most common way that the body absorbs drugs?
- diffusion
- through cell membranes
- determined by concentration gradient
what 2 forms are the drugs that you take in when you take them?
-either ionized or unionized
do protonated drugs pass through the membrane easily?
- no
- remember kid that has static energy… lots of protons
What are the 2 important areas of the body where pH varies and commonly impacts ionization status?
- GI tract
- Kidneys
When PkA=pH, what is the ratio of ionized and unionized drug?
- 50%:50%
- remember it will always add up to 100%
Which kinds of drugs get absorbed??
-unionized drugs
For base drugs, what state will it be in when the pH is high?
-unionized (then it can get absorbed)
for acid drugs, what state will it be in when the pH is low?
-unionized…. so it works at lower pH’s
What do active processes of absorption require?
- Energy
- they can move across concentration gradients
What are the 2 states of drugs related to serum protein binding?
- bound
- unbound
- we are talking about distribution now
Which kind of drug is active, bound, or unbound?
- unbound
- if it is bound to ptn, it can’t work
What is alpha?
- the opposite of % protein bound
- represents the unbound fraction
- the smaller the alpha, the smaller the unbound fraction… makes sense
In metabolism of drugs, what is the phase 1 reaction?
- formation of new or modified functional group or cleavage
- CYP450 (oxidation)
What are phase 2 rxns?
-involve conjugation with an endogenous substance (covalent linkages; glucouronidation…etc)
3 main processes of elimination
- Passive glomerular filtration
- Passive tubular diffusion
- Active tubular secretion
What is First order pharmacokinetics?
- rate of elimination proprtional to Cp, OR
- Amount of drug removed per unit of time will vary proportionately with Cp
- the “linear” type of drug
What is zero order pharmacokinetics?
- saturable (Vmax)
- Rate of elimination not proportional to Cp (concentration in plasma), OR
- fraction of drug removed per unit of time stays the same over time
Assuming first order pharmacokinetics, if you have 100mg/mL at max concentration, how much will there be halfway between that point of zero concentration?
- 50mg/mL
- the fraction lost per unit time never changes
- remember, for first order, the percent lost is always the same
- think of it as half-life! keeps’ halving itself
What is cool about zero order kinetics?
- we lose the same AMOUNT of stuff each time.
- but we lose a larger PERCENT with each time unit
What is MEC
- minimum effective concentration
- look at the drug concentration at the start of duration of action
What is one of the key things that determines C min?
-dosing frequency
