Pharm Equations Quiz 2 Flashcards
What is Absolute Bioavailability?
What is the formula/what is it useful for?
The amount of drug from non iv that reaches circulation relative to an IV dose
Non-IV / IV
Useful when transport of patients is needed (transitioning them back home)
What is Relative Bioavailability?
What is the formula/what is it useful for?
The amount of drug from a non IV formulation that reaches systemic circulation relative to a different non IV formulation
Non-IV / Non- IV
Useful to determine if 2 drugs are bioequivalent when switching meds
What is Vd and what is the equation to determine Vd?
A theoretical volume of fluid that describes relationship of drug dose and plasma concentration characterizes Distribution
Vd = Total amount of drug in the body / Conc of drug in the body
What does a low Vd of a drug mean?
and
What does a high Vd of a drug mean?
Low Vd = drug is restricted to blood (low distribution)
HIgh Vd = drug distributed throughout body
What is the equation for First-Pass Metabolism?
Total Dose - Intestinal Metab - Hepatic Metab = F
F: Bioavailability
How do you determine Renal Clearance?
CLRenal = Renal exretion rate / Plasma drug conc
For which types of drugs is the renal clearance equal to that of Creatine?
- Drugs which undergo glomerular filtration
- Drugs which do NOT undergo extensive reabsorption
What is the formula for total drug Clearance?
How might this information affect dosing?
Total Drug CL = CLRenal + CLHepatic + CLAll Other
Patients with impaired renal or liver function may have decreased drug clearance and may need a dose decrease
What is the General Clearance equation and units?
CL = rate of elimination / Cp
also
Rate of elimination = CL x Cp
Units: L/Hr
What does the Clearance depend on?
- Drug interactions: (Drugs compete for clearance and block removal of other drugs)
- Blood flow (cardiac output)
- Function of elimination organ: comprimised renal func dec clearance
Each drug has a unique CL (Bigger the CL the faster the removal from the body)
What is steady state equilbrium and how long does it take to reach?
the point at which the drug administration is equal to the rate of drug excretion
SS equil is reached in about 4-5 half lifes
and after drug administration stops drug is removed in 4-5 half lives
What is the curve shape of a First- Order Process?
What are its properties with regards to:
Rate of elimination
Half life
First order processs is a log curve and accounts for 95% of drugs
Rate of Elimination: Changes / Is proportional to, the amount of drug present
Half life: Is constant at all points
What is the curve shape of a Zero - Order Process?
What are its properties with regards to:
Rate of elimination
Half life
Is a linear curve which accounts for 5% of drugs and EtOH
Rate of Elimination: Is constant
Half life: decreases as concentration of drug decreases
What is the formula for a loading dose and when is it useful?
How is it administered?
Loading Dose = (Vd x Cp) / F
Vd= volume of distribution
Cp= <b>Target Plasma Concentration</b>
F= Bioavailability
Useful when drugs have long half lifes
Generally given as single dose, unless drug toxic
What is the formula for a maintenance dose and when is it useful?
How is it administered?
Maintenance Dose = (Css x CL) / F
Css = Target Steady-State Concentration
CL = Clearance
F= Bioavailability
Smaller dose to maintain target plasma conc
Generally given repeatedly (4-5 half lifes) until Css reached
What is the balance equation of ligand and receptor for drugs?
and
What do each of the arrow constants relate to?
L + R ⇔ LR
Kon = L + R ⇒ LR
Koff = LR ⇒ L + R
Koff: is a factor of affinity, it is inversely proportional to affinity
Kon: is a factor of concentration has no association with affinity
What is Kd and the formula for it?
and
What are its units and what is it proportional to?
Kd is a dissociation constant
Kd = Koff / Kon
Kd is expressed in units of concentration (molarity)
Kd is inversely proportional to affinity
What is the equation to determine the number of receptors bound by ligand at any given time?
LR = ([L] x Bmax) / (Kd + [L])
What is the equation of fractional occupancy and what is it?
Fractional Occupancy = [L] / ([L] + Kd)
The concentration of Ligand needed to occupy a certain fraction of receptors at a given time
Relative to the Kd what rules of thumb can be used to determine the amount of ligand needed to occupy percentages of receptors?
You need:
[Ligand] = 1/10 Kd
to occupy 10% of receptors
You need:
[Ligand] = 10 x Kd
to occupy ≈ all of receptors
What is the difference between the Kd and the EC50?
Between Emax and Bmax?
Kd is a measure of affinity
EC50 is a measure of potency
Emax: is the maximum level of a certain effect that can be seen
Bmax: is the maximum number of receptors in a system that can be bound
