Unit 1: Pharmacokinetics Flashcards
Pharmacokinetics
What the body does with the drug
Goal of pharmacotherapy
Attain therapeutic effect with minimal toxicity/adverse event
Pharmacokinetics vs pharmacodynamics
What the body does with the drug
vs
From a given concentration, what clinical response might we see?
Clearance
Measure of ability of body to eliminate drug
Volume of distribution
Measure of apparent space in body available to contain drug
i.e. where the drug goes when it is put into the body
Formula for volume of distribution, V
V=(amount of drug in body)/C
C: concentration of drug in blood or plasma
Formula for clearance, CL
CL = (rate of elimination) / C
C: drug concentration
2 major elimination sites
Kidneys
Liver
Renal clearance is ______ ?
Unchanged drug in urine
Liver clearance happens how?
- Unchanged drug secreted via bile and the large intestine
2. Biotransformation of drug into 1+ metabolites
Formula for
Rate of elimination = ?
Rate of elimination = CL x C
Clearance x Concentration
i.e. the area under the curve
FLOW DEPENDENT ELIMINATION
aka ________________
definition: _____________
FLOW DEPENDENT ELIMINATION
aka “first order kinetics” or “first order elimination”
definition: drugs are cleared dependent on blood flow through organ
CAPACITY-LIMITED ELIMINATION
aka ________________
definition: ________________
CAPACITY-LIMITED ELIMINATION
aka “zero order kinetics”
definition: rate of clearance varies depending on concentration of drug achieved (e.g. alcohol) due to pathways becoming saturated
Half life
Amount of time needed to cut amount of drug in half
Steady state is usually attained after ______ half lives
4
Bioavailability
Fraction of unchanged drug reaching systemic circulation following administration by any route
Acidic drugs are better absorbed in ______
Acidic environments like the stomach and small intestines
Alkalotic drugs are uncharged and better absorbed in _______
The small intestine (which is often neutral but sometimes alkalotic)
Maintenance dose
Dose required to reach steady state
Loading dose: why do we give this?
Half life of drug is so long that it would take days to reach steady state; a loading dose promptly raises concentration in plasma to target
Highly protein bound drugs: readily absorbed or not?
Tend to stay in vasculature
Physiologic Variables affecting Pharmacokinetics
— albumin, if drugs are protein bound
— Input: is the patient taking the medication consistently?
— Clearance: abnormalities occur with heart, liver, and kidney failure
— Volume of Distribution: Vd - balance in binding to tissues (decreases plasma volume) and binding to plasma (increases plasma volume)
— Half-life: half life may increase with age but without changes in clearance
The more common kind of elimination
Flow Dependent Elimination
FIRST ORDER ELIMINATION
FIRST ORDER KINETICS
Define: Elimination Constant
amount removed per unit of time
