FIRST ORDER KINETICS, HALF LIFE, SHELF LIFE, ZERO ORDER KINETICS, EXAM 2 QUESTIONS
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FIRST ORDER KINETICS, HALF LIFE, SHELF LIFE,
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FIRST ORDER KINETICS, HALF LIFE, SHELF LIFE,
FIRST ORDER KINETICS, HALF LIFE, SHELF LIFE, ZERO ORDER KINETICS, EXAM 2 QUESTIONSFIRST ORDER KINETICS, HALF LIFE, SHELF LIFE, ZERO ORDER KINETICS, EXAM 2 QUESTIONSFIRST ORDER KINETICS, HALF LIFE, SHELF LIFE, ZERO ORDER KINETICS, EXAM 2 QUESTIONSFIRST ORDER KINETICS, HALF LIFE, SHELF LIFE, ZERO ORD...
FIRST ORDER KINETICS, HALF LIFE, SHELF
LIFE, ZERO ORDER KINETICS, EXAM 2
QUESTIONS
Why is FIRST order kinetics important? - CORRECT ANSWER>>>>It's frequently used
to describe drug degradation kinetics:
In TRUE first order reactions, rate depends on cencentration of one species. In
PSUEDO first order reactions, apparent rate depends on one concentration.
First order kinetics is the basis for pharamcokinetics (PK). - CORRECT
ANSWER>>>>Change with time of drug concentration in plasma.
What is first order kinetics?
In this diagram example, it's the degradation of a drug in aqueous solution. - CORRECT
ANSWER>>>>Reactant (A) degrades to form product (B).
A is the drug, B is the degradation product.
This process is Irreversible.
Concentration of A (CA) decreases with time, as concentration of (CB) increases.
What is first order kinetics?
In this Time (X axis) vs drug concentration (y axis) plot, it shows the degradation of a
drug in aqueous solution. - CORRECT ANSWER>>>>When the drug concentration is
high, the degradation is FAST.
When the durg concentration is low, degradation is SLOW.
Rate of drug degradation is proportional to concentration.
OR
Rate of change of drug concentration with time is proportional to concentration.
OR
dCA / dt = - k CA
In the equation of dCA / dt = - k CA, what does everything stand for? - CORRECT
ANSWER>>>>C A stands for the concentration.
dt represents the time.
k is the rate constant.
dCA / dt = - k CA is a differential equation for the rate of change in DRUG
CONCENTRATION. - CORRECT ANSWER>>>>It's called a "FIRST ORDER"
differential equation because the "C" on the right side appears to the FIRST POWER.
, It's also an "INITIAL VALUE PROBLEM" because we need to know the initial value of C
to get the solution.
So let's say that at t=0, the CA = CA0. - CORRECT ANSWER>>>>The solution to this
differntial equation is:
CA =CA 0 e^ -kt = CA 0 [exp (-kt)]
Fraction of drug remaining at any time is:
CA/CA 0 = e^ -kt = [exp(-kt)]
Taking the natural log of both sides gives us:
ln ( CA/ CA0 ) = -kt
So what does it look like linearly and as a natural log? - CORRECT ANSWER>>>>In
the time x axis vs Ca/Ca0 y axis plot, it's linear. Decreasing k goes up.
In the time x axis and ln(CA/CA0) y axis, the slope is -k, y intercept starts at 0. The
decreasing k goes up.
What is HALF LIFE? - CORRECT ANSWER>>>>Half-life is the time required for the
drug concentration to decrease to one-half of its initial value.
First order kinetics, the half life is related to the rate constant. - CORRECT
ANSWER>>>>At one half life: CA / CA0 = 0.5.
ln(CA/CA0) = ln(0.5) = -0.693.
This means that half life (t1/2) is going to be:
0.693 = k t1/2
t 1/2 = 0.693/k
In the solution at 35ºC and pH 5.8, ampicillin undergoes first order degradation with a
rate constant of 2.7 x 10^-7 s^-1.
What's the degradation half-life, in days? - CORRECT ANSWER>>>>We know that t
1/2 = 0.693/k. Plug in:
t 1/2 = 0.693/( 2.7 x 10^-7 s^-1 ) x day / 86,400 seconds
which gives us 29.7 days.
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