Pharm Equations Quiz 2

Question 1

What is Absolute Bioavailability?

What is the formula/what is it useful for?

Answer 1

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)

Question 2

What is Relative Bioavailability?

What is the formula/what is it useful for?

Answer 2

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

Question 3

What is Vd and what is the equation to determine Vd?

Answer 3

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}

Question 4

What does a low Vd of a drug mean?

and

What does a high Vd of a drug mean?

Answer 4

Low Vd = drug is restricted to blood (low distribution)

HIgh Vd = drug distributed throughout body

Question 5

What is the equation for First-Pass Metabolism?

Answer 5

Total Dose - Intestinal Metab - Hepatic Metab = F

F: Bioavailability

Question 6

How do you determine Renal Clearance?

Answer 6

CL_Renal = ^{Renal exretion rate} / _{Plasma drug conc}

Question 7

For which types of drugs is the renal clearance equal to that of Creatine?

Answer 7

• Drugs which undergo glomerular filtration
• Drugs which do NOT undergo extensive reabsorption

Question 8

What is the formula for total drug Clearance?

How might this information affect dosing?

Answer 8

Total Drug CL = CL_Renal + CL_Hepatic + CL_{All Other}

Patients with impaired renal or liver function may have decreased drug clearance and may need a dose decrease

Question 9

What is the General Clearance equation and units?

Answer 9

CL = ^{rate of elimination} / C_p

_also

Rate of elimination = CL x C_p

_{Units: L/Hr}

Question 10

What does the Clearance depend on?

Answer 10

• 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)

Question 11

What is steady state equilbrium and how long does it take to reach?

Answer 11

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

Question 12

What is the curve shape of a First- Order Process?

What are its properties with regards to:

Rate of elimination

Half life

Answer 12

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

Question 13

What is the curve shape of a Zero - Order Process?

What are its properties with regards to:

Rate of elimination

Half life

Answer 13

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

Question 14

What is the formula for a loading dose and when is it useful?

How is it administered?

Answer 14

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

Question 15

What is the formula for a maintenance dose and when is it useful?

How is it administered?

Answer 15

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

Question 16

What is the balance equation of ligand and receptor for drugs?

_and

What do each of the arrow constants relate to?

Answer 16

L + R ⇔ LR

K_on = L + R ⇒ LR

K_off = LR ⇒ L + R

K_off: is a factor of affinity, it is inversely proportional to affinity

K_on: is a factor of concentration has no association with affinity

Question 17

What is Kd and the formula for it?

and

What are its units and what is it proportional to?

Answer 17

Kd is a dissociation constant

Kd = ^Koff / _Kon

Kd is expressed in units of concentration (molarity)

Kd is inversely proportional to affinity

Question 18

What is the equation to determine the number of receptors bound by ligand at any given time?

Answer 18

LR = ^{([L] x Bmax)} / _{(Kd + [L])}

Question 19

What is the equation of fractional occupancy and what is it?

Answer 19

Fractional Occupancy = ^[L] / _{([L] + Kd)}

The concentration of Ligand needed to occupy a certain fraction of receptors at a given time

Question 20

Relative to the Kd what rules of thumb can be used to determine the amount of ligand needed to occupy percentages of receptors?

Answer 20

You need:

[Ligand] = 1/10 Kd

to occupy 10% of receptors

You need:

[Ligand] = 10 x Kd

to occupy ≈ all of receptors

Question 21

What is the difference between the Kd and the EC50?

Between Emax and Bmax?

Answer 21

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