A Clinicians Guide to Pharmacokinetics Flashcards
What is C”max”?
maximum plasma concentration
What is AUC?
area under plasma concentration vs time curve from time of inj to the limit of quantification of the assay
What is t”max”?
time point @ which C”max” is reached
What is T”1/2”?
plasma half-life of drug
What is t”+0.2”?
time plasma concentrations remain above 0.2 micrograms/mL
how does clinical pharmacokinetics work?
- drug companies work out dosage regime (costs millions of dollars)
- research paper will suggest modifications
- individualizing treatment for specific patient requires that you have an understanding of the basics
What do you know about pharmacodynamics so far?
Dose is not proportional to effect!
What is the therapeutic window?
range btwn minimum EFFECTIVE & minimum TOXIC plasma concentrations in an INDIVIDUAL
(you will not know what these numbers will be)
What is the therapeutic range?
plasma concentration range in POPULATION likely to produce a desired effect
What is pharmacokinetics the study of ?
how drugs get into & out of the body & where they go when they are in the body
why do we need mathematical models?
to develop dosing regimes
What are 2 problems associated with pharmacokinetics?
- math involves logs
- studies are mainly done on blood (plasma) - & most drugs dont work in the blood
what are the clinical limitations of pharmacokinetic data?
- PK data is based on plasma drug concentrations, which may not be as relevant as tissue drug concentrations (ex: UTI)
- PK/PD models
- PK values may be model dependent
- often highly variable btwn studies
- numbers are NOT absolute
Where else can you use drugs that is not in the bloodstream?
Not all drug use is systemic
1. skin
2. ears
3. inhaled
4. intra-mammary
5. intra uterine
6. wounds
what is the problem of extrapolating plasma kinetics?
- most studies are done on sm grps of similar animals & dont account for effects of: age, gender, sex, body type, breed, pregnancy, lactation, &/or genetics
also 2. plasma vs tissue drug concentrations may vary or some drugs get sequestered in fat
How does first order drug elimination work?
- rate of elimination is proportional to amt of drug remaining
- constant PROPORTION of drug is eliminated per unit time
- this results in curved line when plotted on LINEAR/linear graph
- (straight line when plotted on LOG/linear graph)
- most drugs follow 1st order kinetics (@ label doses)!
why do pharmacokineticists tend to stop at 7 half lives?
only 0.8 % of drug remaining
How do you know if graph is linear/linear or log/linear?
look at y axis scale!