Introduction of Pharmacokinetics Flashcards
What is pharmacokinetics?
how the body handles drugs
(ADME)
Explain the dose-effect relationship between pharmacokinetics and pharmacodynamics.
- Dose of drug is administered
- Concentration of drug enters systemic circulation.
- Then either goes to site, distributed to tissues or metabolised and excreted.
These 3 steps are PK
- At site a phamacological effect occurs which can be therapeutic or toxic.
This last step refers to PD
Dose effect relationship
As concentration increases the effect increase
T/F
T
What are the physiologic and pathologic processes that affect drug PK?
What has to be adjusted as a result of these effects
Physiologic processes e.g. body size affect PK parameters ADME
Pathologic processes e.g Heart and renal failure affect PK parameters ADME
The dose has to be adjusted
What are the pharmacokinetic parameters?
Input
Clearance
Volume of distribution
Half life
What does clearance refer to?
CL
A measure of the ability of the body to eliminate the drug
Is the volume of plasma from which a drug is eliminated (metabolism and excretion) per unit time (L/h/70kg)
What does constant clearance mean?
Most drugs follow first-order kinetics, meaning clearance is constant and proportional to drug concentration.
What are the two types of clearance?
- Capacity limited elimination- follows Michaelis Menten Equation e.g. ethanol, aspirin, phenytoin.
- Flow-dependent elimination- high extraction drugs( eliminated as fast as they enter)
What is accumulation?
What is Accumulation factor?
The inverse of elimination
1/Fraction loss in one dosing interval
What is washout period?
giving the body enough time to eliminate drug.
What is VOLUME OF DISTRIBUTION?
This is an apparent volume that relates dose to plasma concentration
What is bioavailability?
What is the bioavailability of IV vs Oral?
Bioavailability is the fraction of unchanged drug reaching the systemic circulation following administration by any route
Bioavailability for IV = 1
Bioavailability for oral < 1
