Key PK properties of a drug

Bioavailability

Vol. of dist.

Clearance

Elimination of Half life

Volume of distribution

An apparent volume that would be necessary in order to account for the initial plasma drug conc. Following a dose of the drug

Units of volume or volume per unit body weight

How to calculate volume of distribution in an animal

Concentration = Dose/plasma conc.

What does volume of distribution allow you to predict

Peak plasma concentration of a drug at a given dose in an animal

When rate of drug movement from blood into tissues is less than rate of drug movement from tissues into blood, is the vol of dist. Large or small.

Very small

3 things that can change Vol D

Body fat

Poor tissue perfusion

Reduction in plasma proteins

1st order kinetics vs. 0 order kinetics

0 order: animal eliminates fixed amount per unit time

1st order: drug eliminated at exponential rate

1st order kinetics properties

Fixed fraction of drug is eliminated per unit time

Can convert to 0 order if the elimination process is saturated

Elimination is proportional to concentration

Half life

A 3 part video game that has left everyone on a cliffhanger for the last 5+ years….damn you valve.

Half life

Time required to eliminate one half of drug present in plasma

-simple units of time

-constant for 1st order drugs

Inversely proportional to the elimination rate constant

What is the number of half lives for a drug to be generally considered eliminated

5 half lives

What are the two phases uses in all PK estimations

1: redistribution phase

2: Elimination phase

What phase do you use while calculating half life

Base it off of elimination phase

If a drug was administered IV what is the bioavailability

100%

How to find initial plasma concentration when not given

Follow the elimination phase line back to the initial time

Is half life used for drug concentration in tissue

No

What does the time to achieve steady state of drug conc in plasma depend on

Half life of the drug

About how many half life’s does it take for a drug to reach steady state

5

Steady state levels of peak and trough are determined by

Drug dose and dosing frequency interval

Calculation of CpMAX for multi dose

=Dose X F X R / VD

Same as single dose except R is included

R in the Multidose treatment formulae

Ratio of dose interval/ interval half life

Peak to trough ratio

Fucntion of dose interval relative to half life

When dose interval equals Half life, CpMIN = 1/2 CpMAX