Pharmacokinetics Flashcards
Pharmacokinetics
a quantitative approach to describe behavior of a drug in the body (what does the body to to the drug)
Pharmacodynamics
impact of drugs in the body (what does the drug do to the body)
Absorption
movement of drug from site of admin. to bloodstream
Very small drugs pass how?
Channels or pores
Selective molecule carriers like transport proteins pass how?
Transport system
Lipid soluble drugs pass how?
Direct penetration across the cell membrane (most common)
Percentage of drug that is in each form at a given time depends on?
pH of the surrounding medium
Acidic drugs ionize in?
basic(alkaline) media
Basic drugs ionize in?
acidic media
Bioavailability
% of drug available in bloodstream after administration compared to IV route
IV route bioavailability?
100%
Factors that affect oral absorption?
bowel resections, diarrhea/constipation, stomach acidity, food, lipid solubility, rate of dissolution
Factors that affect topical absorption?
infant skin, broken or rashy skin, and heat make skin more absorbent
Other factors that affect absorption?
greater blood flow at absorption site= faster absorption
Drug distribution
movement of drug into body fluids and tissues
Volume of Distribution (Vd)
math concept describing amount of drug in body in relation to concentration of drug in blood
Loading dose
give extra drug up front to get things going, drug has large Vd
6 places drugs get distributed in the body
Blood brain barrier (lipid soluble), placental barrier (lipid soluble), breast milk, blood proteins (albumin), fluid areas, lipid/adipose tissue
Drugs bound to plasma proteins are pharmacologically _______ while bound
inactive
Binding is ______ and ________
reversible and not permanent
Protein binding
some drugs are bound to plasma proteins, mostly albumin
Variables affecting Vd and Distribution - infants
body composition of infants are > % of water with < % muscle
Variables affecting Vd and Distribution - obese pt’s
larger than expected volume of distribution for drugs that are highly distributed into adipose tissue
Variables affecting Vd and Distribution - cachetic (frail) pt’s
have less serum proteins available for binding, neonates and elders have more permeable blood brain barriers
Metabolism is?
chemical alteration of the parent compound, resulting in enhanced excretion, inactivation, or active metabolites
Where does metabolism occur?
mainly liver (can also occur in GI tract, lungs, blood, kidneys, nerve terminals)
Prodrug
inactive compound that must be metabolized to become active
Inactive metabolite
de-activated molecule, not pharmacologically active
Active metabolite
active molecule but is different than the parent drug; does not have pharmocologically active properties
First pass metabolism
drugs absorbed in sm. intestine are first exposed to liver and may be metabolized before becoming systemic
First pass metabolism can greatly ______ oral _______
lower; bioavailability
Process by which the drug is eliminated from the body
excretion
Where are most drugs excreted from?
kidneys (can also occur in bile, intestine, lungs, skin)
Drug Clearance is?
volume of blood that is completely cleared of a drug per unit of time
How are drugs cleared?
Some through metabolism, some through excretion, and most are through both
What is the time required for the drug’s plasma concentration to be reduced by half?
half-life (t 1/2)
How many half lives to be cleared from body?
4-5; usually 5
Linear Kinetics
as the dose is increased the level in the blood goes up, half life does not change
Michaelis-Menten Kinetics
non-linear kinetics
Variables that affect clearance (metabolism/excretion)
Age, gender, interacting medications, ethnicity/genetics/heredity, health
