Unit 1 Pharmacokinetic Principles Flashcards
Discuss the pharmacokinetic principles of Distribution.
- Factors influencing drug distribution
- Volume of Distribution
- Loading Dose
What are the factors that influence drug distribution?
- Blood flow to the area of action
- membrane permeability
- Plasma protein binding
Give an example how blood flow to the area of action can influence drug distribution.
Blood Brain Barrier
Prostate
Give an example how membrane permeability can influence drug distribution.
Lipophilic drugs readily cross the BBB (vs hydrophilic)
Give an example how plasma protein binding can influence drug distribution.
higher protein binding decreases unbound or “free” drug in the blood; only unbound drug can exert pharmacologic effect
A drug that is protein bound or unbound has the best chance of crossing the BBB?
Unbound
Bound or unbound proteins are less active?
Bound
Phenytoin is a 90% protein bound drug; 10% is free or unbound. What percentage is going to cross the BBB?
Unbound/free = 10%; need to give a high enough does to equal that 10%.
Vd
Volume of distribution
The apparent volume into which a drug distributes in the body at equilibrium.
Vd (volume of distribution)
the volume that would be required to contain the administered dose if that dose was evenly distributed in blood or plasma
Vd
Vd = __________ divided by ____________
amount in body (mg) / plasma drug concentration (mg/L)
An initial dose that is larger than subsequent doses for the purpose of achieving therapeutic drug concentrations more rapidly
Loading Dose
Loading dose = ________ x ___________
LD = Vd x Cp
Where are most drugs primarily metabolized?
Liver
What does metabolism do to drugs?
process makes the drug more water soluble to be eliminated.
List the factors that influence metabolism.
- Hepatic dysfunction (in liver)
- Severe CHF (decrease blood flow via liver)
- Advanced age (slower metabolism)
Metabolism slows down at what age?
65yrs
Phase I Reactions, Phase II Reactions, Prodrugs, and Active metabolites all would be classified under what pharmacokinetic principle?
Metabolism
When a drug is oxidized or reduced to more polar form?
Phase I Reaction
A Phase 1 Reaction makes a drug more water soluble or less water soluble?
More polar = more water soluble
Cytochrome P450 system is a Phase 1 Reaction or Phase 2 Reaction?
Phase I Reaction